Oracle Linux ® Administrator's Guide for Release 6

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Oracle® Linux
Administrator's Guide for Release 6
E41138-13
November 2014
Oracle® Linux: Administrator's Guide for Release 6
Copyright © 2013, 2014, Oracle and/or its affiliates. All rights reserved.
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Abstract
This manual provides an introduction to administering various features of Oracle Linux systems.
Document generated on: 2014-11-11 (revision: 2355)
Table of Contents
Preface .............................................................................................................................................. xi
I System Configuration ....................................................................................................................... 1
1 The Unbreakable Linux Network .............................................................................................. 7
1.1 About the Unbreakable Linux Network ........................................................................... 7
1.2 About ULN Channels .................................................................................................... 7
1.3 About Software Errata .................................................................................................. 9
1.4 Registering as a ULN User ........................................................................................... 9
1.5 Registering an Oracle Linux 6 or Oracle Linux 7 System ............................................... 10
1.6 Registering an Oracle Linux 4 or Oracle Linux 5 System ............................................... 10
1.7 Configuring an Oracle Linux 5 System to Use yum with ULN ......................................... 10
1.8 Disabling Package Updates ......................................................................................... 11
1.9 Subscribing Your System to ULN Channels ................................................................. 11
1.10 Browsing and Downloading Errata Packages .............................................................. 12
1.11 Downloading Available Errata for a System ................................................................ 12
1.12 Updating System Details ........................................................................................... 13
1.13 Deleting a System .................................................................................................... 13
1.14 About CSI Administration .......................................................................................... 13
1.14.1 Becoming a CSI Administrator ........................................................................ 14
1.14.2 Listing Active CSIs and Transferring Their Registered Servers .......................... 15
1.14.3 Listing Expired CSIs and Transferring Their Registered Servers ........................ 16
1.14.4 Removing a CSI Administrator ........................................................................ 17
1.15 Switching from RHN to ULN ...................................................................................... 17
1.16 For More Information About ULN ............................................................................... 18
2 Yum ...................................................................................................................................... 19
2.1 About Yum ................................................................................................................. 19
2.2 Yum Configuration ...................................................................................................... 19
2.2.1 Configuring Use of a Proxy Server .................................................................... 20
2.2.2 Yum Repository Configuration .......................................................................... 21
2.3 Downloading the Oracle Public Yum Repository Files ................................................... 21
2.4 Using Yum from the Command Line ............................................................................ 22
2.5 Yum Groups ............................................................................................................... 23
2.6 Installing and Using the Yum Security Plugin ............................................................... 23
2.7 Switching CentOS or Scientific Linux Systems to Use the Oracle Public Yum Server ....... 26
2.8 Creating and Using a Local ULN Mirror ....................................................................... 26
2.8.1 Prerequisites for the Local ULN Mirror .............................................................. 26
2.8.2 Setting up a Local ULN Mirror .......................................................................... 27
2.8.3 ULN Mirror Configuration .................................................................................. 30
2.8.4 Updating the Repositories on a Local ULN Mirror .............................................. 30
2.8.5 Configuring yum on a Local ULN Mirror ............................................................ 31
2.8.6 Configuring Oracle Linux Yum Clients of a Local ULN Mirror .............................. 31
2.9 Creating a Local Yum Repository Using an ISO Image ................................................. 33
2.10 Setting up a Local Yum Server Using an ISO Image ................................................... 34
2.11 For More Information About Yum ............................................................................... 35
3 Ksplice Uptrack ..................................................................................................................... 37
3.1 About Ksplice Uptrack ................................................................................................. 37
3.1.1 Supported Kernels ........................................................................................... 37
3.2 Registering to Use Ksplice Uptrack .............................................................................. 38
3.3 Installing Ksplice Uptrack ............................................................................................ 38
3.4 Configuring Ksplice Uptrack ........................................................................................ 39
3.5 Managing Ksplice Updates .......................................................................................... 40
3.6 Patching and Updating Your System ........................................................................... 41
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3.7 Removing the Ksplice Uptrack software ....................................................................... 41
3.8 About Ksplice Offline Client ......................................................................................... 41
3.8.1 Modifying a Local Yum Server to Act as a Ksplice Mirror .................................... 41
3.8.2 Configuring Ksplice Offline Clients .................................................................... 42
3.9 For More Information About Ksplice Uptrack ................................................................ 44
Boot Configuration ................................................................................................................. 45
4.1 About the Boot Process .............................................................................................. 45
4.2 About the GRUB Boot Loader ..................................................................................... 46
4.2.1 About the GRUB Configuration File ................................................................... 47
4.2.2 Configuring a GRUB Password ......................................................................... 50
4.2.3 Using GRUB .................................................................................................... 51
4.3 About Run Levels ....................................................................................................... 51
4.3.1 Displaying the Run Level .................................................................................. 52
4.3.2 Changing the Run Level ................................................................................... 52
4.3.3 Shutting down the System ................................................................................ 52
4.3.4 About Service Scripts ....................................................................................... 52
4.3.5 About the Service Configuration GUI ................................................................. 53
4.3.6 Starting and Stopping Services ......................................................................... 54
4.3.7 Configuring Services to Start at Different Run Levels ......................................... 54
System Configuration Settings ............................................................................................... 57
5.1 About /etc/sysconfig Files ............................................................................................ 57
5.2 About the /proc Virtual File System .............................................................................. 58
5.2.1 Virtual Files and Directories Under /proc ........................................................... 59
5.2.2 Changing Kernel Parameters ............................................................................ 62
5.2.3 Parameters that Control System Performance ................................................... 63
5.2.4 Parameters that Control Kernel Panics .............................................................. 64
5.3 About the /sys Virtual File System ............................................................................... 65
5.3.1 Virtual Directories Under /sys ............................................................................ 65
Kernel Modules ..................................................................................................................... 67
6.1 About Kernel Modules ................................................................................................. 67
6.2 Listing Information about Loaded Modules ................................................................... 67
6.3 Loading and Unloading Modules ................................................................................. 68
6.4 About Module Parameters ........................................................................................... 69
6.5 Specifying Modules to be Loaded at Boot Time ............................................................ 70
Device Management .............................................................................................................. 71
7.1 About Device Files ...................................................................................................... 71
7.2 About the Udev Device Manager ................................................................................. 73
7.3 About Udev Rules ...................................................................................................... 73
7.4 Querying Udev and Sysfs ........................................................................................... 76
7.5 Modifying Udev Rules ................................................................................................. 79
Task Management ................................................................................................................. 81
8.1 About Automating Tasks ............................................................................................. 81
8.2 Configuring cron Jobs ................................................................................................. 81
8.2.1 Controlling Access to Running cron Jobs .......................................................... 82
8.3 Configuring anacron Jobs ........................................................................................... 83
8.4 Running One-time Tasks ............................................................................................. 84
8.4.1 Changing the Behavior of Batch Jobs ............................................................... 84
System Monitoring and Tuning ............................................................................................... 87
9.1 About sosreport .......................................................................................................... 87
9.1.1 Configuring and Using sosreport ....................................................................... 87
9.2 About System Performance Tuning ............................................................................. 88
9.2.1 About Performance Problems ........................................................................... 88
9.2.2 Monitoring Usage of System Resources ............................................................ 89
9.2.3 Using the Graphical System Monitor ................................................................. 92
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9.2.4 About OSWatcher Black Box ............................................................................ 92
10 System Dump Analysis ........................................................................................................ 95
10.1 About Kdump ............................................................................................................ 95
10.1.1 Configuring and Using Kdump ........................................................................ 95
10.1.2 Files Used by Kdump ..................................................................................... 97
10.1.3 Using Kdump with OCFS2 .............................................................................. 97
10.1.4 Using Kdump with a System Hang .................................................................. 98
10.2 Using the crash Debugger ......................................................................................... 98
10.2.1 Installing the crash Packages ......................................................................... 98
10.2.2 Running crash ................................................................................................ 99
10.2.3 Kernel Data Structure Analysis Commands .................................................... 100
10.2.4 System State Commands ............................................................................. 102
10.2.5 Helper Commands ....................................................................................... 105
10.2.6 Session Control Commands .......................................................................... 105
10.2.7 Guidelines for Examining a Dump File ........................................................... 106
II Networking and Network Services ................................................................................................ 107
11 Network Configuration ........................................................................................................ 111
11.1 About Network Interfaces ........................................................................................ 111
11.2 About Network Configuration Files ........................................................................... 113
11.2.1 /etc/hosts ...................................................................................................... 113
11.2.2 /etc/nsswitch.conf .......................................................................................... 113
11.2.3 /etc/resolv.conf ............................................................................................. 113
11.2.4 /etc/sysconfig/network ................................................................................... 114
11.3 Command-line Network Configuration Interfaces ....................................................... 114
11.4 Configuring Network Interfaces Using Graphical Interfaces ........................................ 116
11.5 Configuring Network Interface Bonding .................................................................... 117
11.5.1 Using ifenslave to Create Bonded Interfaces .................................................. 118
11.6 Configuring VLANs with Untagged Data Frames ....................................................... 119
11.6.1 Using vconfig to Create VLAN Devices .......................................................... 120
11.7 Configuring Network Routing ................................................................................... 120
12 Network Address Configuration .......................................................................................... 123
12.1 About the Dynamic Host Configuration Protocol ........................................................ 123
12.2 Configuring a DHCP Server ..................................................................................... 123
12.3 Configuring a DHCP Client ...................................................................................... 124
12.4 About Network Address Translation ......................................................................... 125
13 Name Service Configuration ............................................................................................... 127
13.1 About DNS and BIND ............................................................................................. 127
13.2 About Types of Name Servers ................................................................................. 128
13.3 About DNS Configuration Files ................................................................................ 128
13.3.1 /etc/named.conf ............................................................................................ 128
13.3.2 About Resource Records in Zone Files ......................................................... 131
13.3.3 About Resource Records for Reverse-name Resolution .................................. 132
13.4 Configuring a Name Server ..................................................................................... 133
13.5 Administering the Name Service .............................................................................. 134
13.6 Performing DNS Lookups ........................................................................................ 135
14 Network Time Configuration ............................................................................................... 137
14.1 About the NTP Daemon .......................................................................................... 137
14.1.1 Configuring the ntpd Service ......................................................................... 137
14.2 About PTP .............................................................................................................. 138
14.2.1 Configuring the PTP Service ......................................................................... 139
14.2.2 Using PTP as a Time Source for NTP ........................................................... 141
15 Web Service Configuration ................................................................................................. 143
15.1 About the Apache HTTP Server .............................................................................. 143
15.2 Installing the Apache HTTP Server .......................................................................... 143
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15.3 Configuring the Apache HTTP Server ......................................................................
15.4 Testing the Apache HTTP Server ............................................................................
15.5 Configuring Apache Containers ................................................................................
15.5.1 About Nested Containers ..............................................................................
15.6 Configuring Apache Virtual Hosts .............................................................................
16 Email Service Configuration ...............................................................................................
16.1 About Email Programs ............................................................................................
16.2 About Email Protocols .............................................................................................
16.2.1 About SMTP ................................................................................................
16.2.2 About POP and IMAP ..................................................................................
16.3 About the Postfix SMTP Server ...............................................................................
16.4 About the Sendmail SMTP Server ...........................................................................
16.4.1 About Sendmail Configuration Files ...............................................................
16.5 Forwarding Email ....................................................................................................
16.6 Configuring a Sendmail Client .................................................................................
III Storage and File Systems ...........................................................................................................
17 Storage Management .........................................................................................................
17.1 About Disk Partitions ...............................................................................................
17.1.1 Managing Partition Tables Using fdisk ...........................................................
17.1.2 Managing Partition Tables Using parted ........................................................
17.1.3 Mapping Partition Tables to Devices .............................................................
17.2 About Swap Space .................................................................................................
17.2.1 Viewing Swap Space Usage .........................................................................
17.2.2 Creating and Using a Swap File ....................................................................
17.2.3 Creating and Using a Swap Partition .............................................................
17.2.4 Removing a Swap File or Swap Partition .......................................................
17.3 About Logical Volume Manager ...............................................................................
17.3.1 Initializing and Managing Physical Volumes ...................................................
17.3.2 Creating and Managing Volume Groups ........................................................
17.3.3 Creating and Managing Logical Volumes .......................................................
17.4 About Software RAID ..............................................................................................
17.4.1 Creating Software RAID Devices ...................................................................
17.5 Creating Encrypted Block Devices ...........................................................................
17.6 About iSCSI Storage ...............................................................................................
17.6.1 Configuring an iSCSI Target .........................................................................
17.6.2 Configuring an iSCSI Initiator ........................................................................
17.6.3 Updating the Discovery Database .................................................................
17.7 About Device Multipathing .......................................................................................
17.7.1 Configuring Multipathing ...............................................................................
18 File System Administration .................................................................................................
18.1 Making File Systems ...............................................................................................
18.2 Mounting File Systems ............................................................................................
18.2.1 About Mount Options ....................................................................................
18.3 About the File System Mount Table .........................................................................
18.4 Configuring the Automounter ...................................................................................
18.5 Mounting a File Containing a File System Image ......................................................
18.6 Creating a File System on a File .............................................................................
18.7 Checking and Repairing a File System .....................................................................
18.7.1 Changing the Frequency of File System Checking ..........................................
18.8 About Access Control Lists ......................................................................................
18.8.1 Configuring ACL Support ..............................................................................
18.8.2 Setting and Displaying ACLs .........................................................................
18.9 About Disk Quotas ..................................................................................................
18.9.1 Enabling Disk Quotas on File Systems ..........................................................
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18.9.2 Assigning Disk Quotas to Users and Groups ................................................. 193
18.9.3 Setting the Grace Period .............................................................................. 194
18.9.4 Displaying Disk Quotas ................................................................................. 194
18.9.5 Enabling and Disabling Disk Quotas .............................................................. 194
18.9.6 Reporting on Disk Quota Usage .................................................................... 194
18.9.7 Maintaining the Accuracy of Disk Quota Reporting ......................................... 195
19 Local File System Administration ........................................................................................ 197
19.1 About Local File Systems ........................................................................................ 198
19.2 About the Btrfs File System ..................................................................................... 199
19.3 Creating a Btrfs File System .................................................................................... 199
19.4 Modifying a Btrfs File System .................................................................................. 201
19.5 Compressing and Defragmenting a Btrfs File System ................................................ 201
19.6 Resizing a Btrfs File System .................................................................................... 202
19.7 Creating Subvolumes and Snapshots ....................................................................... 202
19.7.1 Cloning Virtual Machine Images and Linux Containers .................................... 204
19.8 Using the Send/Receive Feature ............................................................................. 204
19.8.1 Using Send/Receive to Implement Incremental Backups ................................. 205
19.9 Using Quota Groups ............................................................................................... 205
19.10 Replacing Devices on a Live File System ............................................................... 206
19.11 Creating Snapshots of Files ................................................................................... 206
19.12 Converting an Ext2, Ext3, or Ext4 File System to a Btrfs File System ........................ 206
19.12.1 Converting a Non-root File System .............................................................. 207
19.12.2 Converting the root File System .................................................................. 207
19.12.3 Mounting the Image of the Original File System ........................................... 209
19.12.4 Deleting the Snapshot of the Original File System ........................................ 209
19.12.5 Recovering an Original Non-root File System ............................................... 209
19.13 Installing a Btrfs root File System ........................................................................... 210
19.13.1 Setting up a New NFS Server ..................................................................... 210
19.13.2 Configuring an Existing NFS Server ............................................................ 211
19.13.3 Setting up a New HTTP Server ................................................................... 211
19.13.4 Configuring an Existing HTTP Server .......................................................... 212
19.13.5 Setting up a Network Installation Server ...................................................... 213
19.13.6 Installing from a Network Installation Server ................................................. 214
19.13.7 About the Installation root File System ......................................................... 215
19.13.8 Creating Snapshots of the root File System ................................................. 216
19.13.9 Mounting Alternate Snapshots as the root File System ................................. 216
19.13.10 Deleting Snapshots of the root File System ................................................ 216
19.14 Converting a Non-root Ext2 File System to Ext3 ..................................................... 217
19.15 Converting a root Ext2 File System to Ext3 ............................................................ 217
19.16 Creating a Local OCFS2 File System ..................................................................... 219
19.17 About the XFS File System ................................................................................... 219
19.17.1 About External XFS Journals ...................................................................... 220
19.17.2 About XFS Write Barriers ............................................................................ 221
19.17.3 About Lazy Counters .................................................................................. 221
19.18 Installing the XFS Packages .................................................................................. 221
19.19 Creating an XFS File System ................................................................................ 221
19.20 Modifying an XFS File System ............................................................................... 222
19.21 Growing an XFS File System ................................................................................. 223
19.22 Freezing and Unfreezing an XFS File System ......................................................... 223
19.23 Setting Quotas on an XFS File System .................................................................. 223
19.23.1 Setting Project Quotas ................................................................................ 224
19.24 Backing up and Restoring XFS File Systems .......................................................... 225
19.25 Defragmenting an XFS File System ....................................................................... 227
19.26 Checking and Repairing an XFS File System .......................................................... 227
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20 Shared File System Administration ..................................................................................... 229
20.1 About Shared File Systems ..................................................................................... 229
20.2 About NFS .............................................................................................................. 229
20.2.1 Configuring an NFS Server ........................................................................... 231
20.2.2 Mounting an NFS File System ...................................................................... 234
20.3 About Samba .......................................................................................................... 234
20.3.1 Configuring a Samba Server ......................................................................... 234
20.3.2 About Samba Configuration for Windows Workgroups and Domains ................ 236
20.3.3 Accessing Samba Shares from a Windows Client .......................................... 239
20.3.4 Accessing Samba Shares from an Oracle Linux Client ................................... 239
21 Oracle Cluster File System Version 2 ................................................................................. 241
21.1 About OCFS2 ......................................................................................................... 241
21.2 Installing and Configuring OCFS2 ............................................................................ 242
21.2.1 Preparing a Cluster for OCFS2 ..................................................................... 243
21.2.2 Configuring the Firewall ................................................................................ 244
21.2.3 Configuring the Cluster Software ................................................................... 244
21.2.4 Creating the Configuration File for the Cluster Stack ....................................... 244
21.2.5 Configuring the Cluster Stack ........................................................................ 247
21.2.6 Configuring the Kernel for Cluster Operation .................................................. 248
21.2.7 Starting and Stopping the Cluster Stack ........................................................ 249
21.2.8 Creating OCFS2 volumes ............................................................................. 249
21.2.9 Mounting OCFS2 Volumes ........................................................................... 251
21.2.10 Querying and Changing Volume Parameters ................................................ 251
21.3 Troubleshooting OCFS2 .......................................................................................... 251
21.3.1 Recommended Tools for Debugging ............................................................. 251
21.3.2 Mounting the debugfs File System ................................................................ 252
21.3.3 Configuring OCFS2 Tracing .......................................................................... 252
21.3.4 Debugging File System Locks ....................................................................... 253
21.3.5 Configuring the Behavior of Fenced Nodes .................................................... 255
21.4 Use Cases for OCFS2 ............................................................................................ 255
21.4.1 Load Balancing ............................................................................................ 255
21.4.2 Oracle Real Application Cluster (RAC) .......................................................... 255
21.4.3 Oracle Databases ......................................................................................... 256
21.5 For More Information About OCFS2 ......................................................................... 256
IV Authentication and Security ........................................................................................................ 257
22 Authentication Configuration ............................................................................................... 261
22.1 About Authentication ............................................................................................... 261
22.2 About Local Oracle Linux Authentication .................................................................. 262
22.2.1 Configuring Local Access ............................................................................. 263
22.2.2 Configuring Fingerprint Reader Authentication ............................................... 265
22.2.3 Configuring Smart Card Authentication .......................................................... 265
22.3 About IPA ............................................................................................................... 266
22.3.1 Configuring IPA ............................................................................................ 266
22.4 About LDAP Authentication ..................................................................................... 266
22.4.1 About LDAP Data Interchange Format ........................................................... 267
22.4.2 Configuring an LDAP Server ......................................................................... 267
22.4.3 Replacing the Default Certificates ................................................................. 270
22.4.4 Creating and Distributing Self-signed CA Certificates ...................................... 271
22.4.5 Initializing an Organization in LDAP ............................................................... 274
22.4.6 Adding an Automount Map to LDAP .............................................................. 275
22.4.7 Adding a Group to LDAP .............................................................................. 275
22.4.8 Adding a User to LDAP ................................................................................ 276
22.4.9 Adding Users to a Group in LDAP ................................................................ 278
22.4.10 Enabling LDAP Authentication ..................................................................... 279
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22.5 About NIS Authentication ......................................................................................... 283
22.5.1 About NIS Maps ........................................................................................... 284
22.5.2 Configuring an NIS Server ............................................................................ 284
22.5.3 Adding User Accounts to NIS ....................................................................... 288
22.5.4 Enabling NIS Authentication .......................................................................... 289
22.6 About Kerberos Authentication ................................................................................. 291
22.6.1 Configuring a Kerberos Server ...................................................................... 294
22.6.2 Configuring a Kerberos Client ....................................................................... 296
22.6.3 Enabling Kerberos Authentication .................................................................. 297
22.7 About Pluggable Authentication Modules .................................................................. 300
22.7.1 Configuring Pluggable Authentication Modules ............................................... 300
22.8 About the System Security Services Daemon ........................................................... 301
22.8.1 Configuring an SSSD Server ........................................................................ 302
22.9 About Winbind Authentication .................................................................................. 304
22.9.1 Enabling Winbind Authentication ................................................................... 304
23 Local Account Configuration ............................................................................................... 307
23.1 About User and Group Configuration ....................................................................... 307
23.2 Changing Default Settings for User Accounts ........................................................... 308
23.3 Creating User Accounts ........................................................................................... 308
23.3.1 About umask and the setgid and Restricted Deletion Bits ................................ 309
23.4 Locking an Account ................................................................................................. 309
23.5 Modifying or Deleting User Accounts ........................................................................ 309
23.6 Creating Groups ...................................................................................................... 310
23.7 Modifying or Deleting Groups .................................................................................. 310
23.8 Configuring Password Ageing .................................................................................. 310
23.9 Granting sudo Access to Users ............................................................................... 311
24 System Security Administration .......................................................................................... 313
24.1 About System Security ............................................................................................ 313
24.2 Configuring and Using SELinux ............................................................................... 314
24.2.1 About SELinux Administration ....................................................................... 315
24.2.2 About SELinux Modes .................................................................................. 317
24.2.3 Setting SELinux Modes ................................................................................ 317
24.2.4 About SELinux Policies ................................................................................. 317
24.2.5 About SELinux Context ................................................................................. 319
24.2.6 About SELinux Users ................................................................................... 321
24.2.7 Troubleshooting Access-Denial Messages ..................................................... 322
24.3 About Packet-filtering Firewalls ................................................................................ 323
24.3.1 Controlling the Firewall Service ..................................................................... 325
24.3.2 Listing Firewall Rules ................................................................................... 325
24.3.3 Inserting and Replacing Rules in a Chain ...................................................... 326
24.3.4 Deleting Rules in a Chain ............................................................................. 327
24.3.5 Saving Rules ................................................................................................ 327
24.4 About TCP Wrappers .............................................................................................. 327
24.5 About chroot Jails ................................................................................................... 329
24.5.1 Running DNS and FTP Services in a Chroot Jail ............................................ 329
24.5.2 Creating a Chroot Jail .................................................................................. 329
24.5.3 Using a Chroot Jail ...................................................................................... 330
24.6 About Auditing ........................................................................................................ 330
24.7 About System Logging ............................................................................................ 331
24.7.1 Configuring Logwatch ................................................................................... 334
24.8 About Process Accounting ....................................................................................... 335
24.9 Security Guidelines ................................................................................................. 335
24.9.1 Minimizing the Software Footprint ................................................................. 335
24.9.2 Configuring System Logging ......................................................................... 337
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24.9.3 Disabling Core Dumps .................................................................................. 337
24.9.4 Minimizing Active Services ............................................................................ 337
24.9.5 Locking Down Network Services ................................................................... 340
24.9.6 Configuring a Packet-filtering Firewall ............................................................ 341
24.9.7 Configuring TCP Wrappers ........................................................................... 341
24.9.8 Configuring Kernel Parameters ..................................................................... 341
24.9.9 Restricting Access to SSH Connections ......................................................... 342
24.9.10 Configuring File System Mounts, File Permissions, and File Ownerships ........ 342
24.9.11 Checking User Accounts and Privileges ....................................................... 344
25 OpenSSH Configuration ..................................................................................................... 347
25.1 About OpenSSH ..................................................................................................... 347
25.2 OpenSSH Configuration Files .................................................................................. 347
25.2.1 OpenSSH User Configuration Files ............................................................... 348
25.3 Configuring an OpenSSH Server ............................................................................. 349
25.4 Installing the OpenSSH Client Packages .................................................................. 349
25.5 Using the OpenSSH Utilities .................................................................................... 349
25.5.1 Using ssh to Connect to Another System ....................................................... 350
25.5.2 Using scp and sftp to Copy Files Between Systems ....................................... 351
25.5.3 Using ssh-keygen to Generate Pairs of Authentication Keys ............................ 352
25.5.4 Enabling Remote System Access Without Requiring a Password .................... 352
x
Preface
The Oracle Linux Administrator's Guide provides introductory information about administering various
features of Oracle Linux systems, including system configuration, networking, network services, storage
devices, file systems, authentication, and security.
Audience
This document is intended for administrators who need to configure and administer Oracle Linux. It is
assumed that readers are familiar with web technologies and have a general understanding of using the
Linux operating system, including knowledge of how to use a text editor such as emacs or vim, essential
commands such as cd, chmod, chown, ls, mkdir, mv, ps, pwd, and rm, and using the man command to
view manual pages.
Document Organization
The document is organized as follows:
• Part I, “System Configuration” describes how to configure software and kernel updates, booting, kernel
and module settings, and devices, how to schedule tasks, and how to monitor and tune your system.
• Part II, “Networking and Network Services” describes how to configure network interfaces, network
addresses, name service, network time services, and basic web and email services.
• Part III, “Storage and File Systems” describes how to configure storage devices and how to create and
manage local, shared, and cluster file systems.
• Part IV, “Authentication and Security” describes how to configure user account databases and
authentication, how to add group and user accounts, how to administer essential aspects of system
security, and how to configure and use the OpenSSH tools.
Documentation Accessibility
For information about Oracle's commitment to accessibility, visit the Oracle Accessibility Program website
at http://www.oracle.com/pls/topic/lookup?ctx=acc&id=docacc.
Access to Oracle Support
Oracle customers have access to electronic support through My Oracle Support. For information, visit
http://www.oracle.com/pls/topic/lookup?ctx=acc&id=info or visit http://www.oracle.com/pls/topic/lookup?
ctx=acc&id=trs if you are hearing impaired.
Related Documents
The documentation for this product is available at:
http://www.oracle.com/technetwork/server-storage/linux/documentation/index.html.
Conventions
The following text conventions are used in this document:
Convention
Meaning
boldface
Boldface type indicates graphical user interface elements associated with an
action, or terms defined in text or the glossary.
xi
Convention
Meaning
italic
Italic type indicates book titles, emphasis, or placeholder variables for which
you supply particular values.
monospace
Monospace type indicates commands within a paragraph, URLs, code in
examples, text that appears on the screen, or text that you enter.
xii
Part I System Configuration
This section contains the following chapters:
• Chapter 1, The Unbreakable Linux Network describes how to access and use the software channels that are
available on the Unbreakable Linux Network (ULN).
• Chapter 2, Yum describes how you can use the yum utility to install and upgrade software packages.
• Chapter 3, Ksplice Uptrack describes how to configure Ksplice Uptrack to update the kernel on a running system.
• Chapter 4, Boot Configuration describes the Oracle Linux boot process, how to use the GRUB boot loader, how to
change the run level of a system, and how to configure the services that are available at each run level.
• Chapter 5, System Configuration Settings describes the files and virtual file systems that you can use to change
configuration settings for your system.
• Chapter 6, Kernel Modules describes how to load, unload, and modify the behavior of kernel modules.
• Chapter 7, Device Management describes how the system uses device files and how the udev device manager
dynamically creates or removes device node files.
• Chapter 8, Task Management describes how to configure the system to run tasks automatically within a specific
period of time, at a specified time and date, or when the system is lightly loaded.
• Chapter 9, System Monitoring and Tuning describes how to collect diagnostic information about a system for Oracle
Support, and how to monitor and tune the performance of a system.
• Chapter 10, System Dump Analysis describes how to configure a system to create a memory image in the event
of a system crash, and how to use the crash debugger to analyse the memory image in a crash dump or for a live
system.
Table of Contents
1 The Unbreakable Linux Network ...................................................................................................... 7
1.1 About the Unbreakable Linux Network ................................................................................... 7
1.2 About ULN Channels ............................................................................................................ 7
1.3 About Software Errata .......................................................................................................... 9
1.4 Registering as a ULN User ................................................................................................... 9
1.5 Registering an Oracle Linux 6 or Oracle Linux 7 System ...................................................... 10
1.6 Registering an Oracle Linux 4 or Oracle Linux 5 System ...................................................... 10
1.7 Configuring an Oracle Linux 5 System to Use yum with ULN ................................................ 10
1.8 Disabling Package Updates ................................................................................................ 11
1.9 Subscribing Your System to ULN Channels ......................................................................... 11
1.10 Browsing and Downloading Errata Packages ..................................................................... 12
1.11 Downloading Available Errata for a System ........................................................................ 12
1.12 Updating System Details ................................................................................................... 13
1.13 Deleting a System ............................................................................................................ 13
1.14 About CSI Administration .................................................................................................. 13
1.14.1 Becoming a CSI Administrator ................................................................................ 14
1.14.2 Listing Active CSIs and Transferring Their Registered Servers .................................. 15
1.14.3 Listing Expired CSIs and Transferring Their Registered Servers ................................ 16
1.14.4 Removing a CSI Administrator ................................................................................ 17
1.15 Switching from RHN to ULN .............................................................................................. 17
1.16 For More Information About ULN ....................................................................................... 18
2 Yum .............................................................................................................................................. 19
2.1 About Yum ......................................................................................................................... 19
2.2 Yum Configuration .............................................................................................................. 19
2.2.1 Configuring Use of a Proxy Server ........................................................................... 20
2.2.2 Yum Repository Configuration .................................................................................. 21
2.3 Downloading the Oracle Public Yum Repository Files ........................................................... 21
2.4 Using Yum from the Command Line .................................................................................... 22
2.5 Yum Groups ....................................................................................................................... 23
2.6 Installing and Using the Yum Security Plugin ....................................................................... 23
2.7 Switching CentOS or Scientific Linux Systems to Use the Oracle Public Yum Server ............... 26
2.8 Creating and Using a Local ULN Mirror ............................................................................... 26
2.8.1 Prerequisites for the Local ULN Mirror ...................................................................... 26
2.8.2 Setting up a Local ULN Mirror .................................................................................. 27
2.8.3 ULN Mirror Configuration .......................................................................................... 30
2.8.4 Updating the Repositories on a Local ULN Mirror ...................................................... 30
2.8.5 Configuring yum on a Local ULN Mirror .................................................................... 31
2.8.6 Configuring Oracle Linux Yum Clients of a Local ULN Mirror ...................................... 31
2.9 Creating a Local Yum Repository Using an ISO Image ......................................................... 33
2.10 Setting up a Local Yum Server Using an ISO Image ........................................................... 34
2.11 For More Information About Yum ....................................................................................... 35
3 Ksplice Uptrack ............................................................................................................................. 37
3.1 About Ksplice Uptrack ......................................................................................................... 37
3.1.1 Supported Kernels ................................................................................................... 37
3.2 Registering to Use Ksplice Uptrack ...................................................................................... 38
3.3 Installing Ksplice Uptrack .................................................................................................... 38
3.4 Configuring Ksplice Uptrack ................................................................................................ 39
3.5 Managing Ksplice Updates .................................................................................................. 40
3.6 Patching and Updating Your System ................................................................................... 41
3.7 Removing the Ksplice Uptrack software ............................................................................... 41
3.8 About Ksplice Offline Client ................................................................................................. 41
3
3.8.1 Modifying a Local Yum Server to Act as a Ksplice Mirror ............................................ 41
3.8.2 Configuring Ksplice Offline Clients ............................................................................ 42
3.9 For More Information About Ksplice Uptrack ........................................................................ 44
4 Boot Configuration ......................................................................................................................... 45
4.1 About the Boot Process ...................................................................................................... 45
4.2 About the GRUB Boot Loader ............................................................................................. 46
4.2.1 About the GRUB Configuration File .......................................................................... 47
4.2.2 Configuring a GRUB Password ................................................................................. 50
4.2.3 Using GRUB ............................................................................................................ 51
4.3 About Run Levels ............................................................................................................... 51
4.3.1 Displaying the Run Level .......................................................................................... 52
4.3.2 Changing the Run Level ........................................................................................... 52
4.3.3 Shutting down the System ........................................................................................ 52
4.3.4 About Service Scripts ............................................................................................... 52
4.3.5 About the Service Configuration GUI ........................................................................ 53
4.3.6 Starting and Stopping Services ................................................................................. 54
4.3.7 Configuring Services to Start at Different Run Levels ................................................. 54
5 System Configuration Settings ....................................................................................................... 57
5.1 About /etc/sysconfig Files .................................................................................................... 57
5.2 About the /proc Virtual File System ...................................................................................... 58
5.2.1 Virtual Files and Directories Under /proc ................................................................... 59
5.2.2 Changing Kernel Parameters .................................................................................... 62
5.2.3 Parameters that Control System Performance ........................................................... 63
5.2.4 Parameters that Control Kernel Panics ...................................................................... 64
5.3 About the /sys Virtual File System ....................................................................................... 65
5.3.1 Virtual Directories Under /sys .................................................................................... 65
6 Kernel Modules ............................................................................................................................. 67
6.1 About Kernel Modules ......................................................................................................... 67
6.2 Listing Information about Loaded Modules ........................................................................... 67
6.3 Loading and Unloading Modules ......................................................................................... 68
6.4 About Module Parameters ................................................................................................... 69
6.5 Specifying Modules to be Loaded at Boot Time .................................................................... 70
7 Device Management ...................................................................................................................... 71
7.1 About Device Files .............................................................................................................. 71
7.2 About the Udev Device Manager ......................................................................................... 73
7.3 About Udev Rules .............................................................................................................. 73
7.4 Querying Udev and Sysfs ................................................................................................... 76
7.5 Modifying Udev Rules ......................................................................................................... 79
8 Task Management ......................................................................................................................... 81
8.1 About Automating Tasks ..................................................................................................... 81
8.2 Configuring cron Jobs ......................................................................................................... 81
8.2.1 Controlling Access to Running cron Jobs .................................................................. 82
8.3 Configuring anacron Jobs ................................................................................................... 83
8.4 Running One-time Tasks ..................................................................................................... 84
8.4.1 Changing the Behavior of Batch Jobs ....................................................................... 84
9 System Monitoring and Tuning ....................................................................................................... 87
9.1 About sosreport .................................................................................................................. 87
9.1.1 Configuring and Using sosreport ............................................................................... 87
9.2 About System Performance Tuning ..................................................................................... 88
9.2.1 About Performance Problems ................................................................................... 88
9.2.2 Monitoring Usage of System Resources .................................................................... 89
9.2.3 Using the Graphical System Monitor ......................................................................... 92
9.2.4 About OSWatcher Black Box .................................................................................... 92
10 System Dump Analysis ................................................................................................................ 95
4
10.1 About Kdump .................................................................................................................... 95
10.1.1 Configuring and Using Kdump ................................................................................ 95
10.1.2 Files Used by Kdump ............................................................................................. 97
10.1.3 Using Kdump with OCFS2 ...................................................................................... 97
10.1.4 Using Kdump with a System Hang .......................................................................... 98
10.2 Using the crash Debugger ................................................................................................. 98
10.2.1 Installing the crash Packages ................................................................................. 98
10.2.2 Running crash ........................................................................................................ 99
10.2.3 Kernel Data Structure Analysis Commands ............................................................ 100
10.2.4 System State Commands ..................................................................................... 102
10.2.5 Helper Commands ............................................................................................... 105
10.2.6 Session Control Commands .................................................................................. 105
10.2.7 Guidelines for Examining a Dump File ................................................................... 106
5
6
Chapter 1 The Unbreakable Linux Network
Table of Contents
1.1 About the Unbreakable Linux Network ........................................................................................... 7
1.2 About ULN Channels .................................................................................................................... 7
1.3 About Software Errata .................................................................................................................. 9
1.4 Registering as a ULN User ........................................................................................................... 9
1.5 Registering an Oracle Linux 6 or Oracle Linux 7 System .............................................................. 10
1.6 Registering an Oracle Linux 4 or Oracle Linux 5 System .............................................................. 10
1.7 Configuring an Oracle Linux 5 System to Use yum with ULN ........................................................ 10
1.8 Disabling Package Updates ........................................................................................................ 11
1.9 Subscribing Your System to ULN Channels ................................................................................. 11
1.10 Browsing and Downloading Errata Packages ............................................................................. 12
1.11 Downloading Available Errata for a System ................................................................................ 12
1.12 Updating System Details ........................................................................................................... 13
1.13 Deleting a System .................................................................................................................... 13
1.14 About CSI Administration .......................................................................................................... 13
1.14.1 Becoming a CSI Administrator ........................................................................................ 14
1.14.2 Listing Active CSIs and Transferring Their Registered Servers .......................................... 15
1.14.3 Listing Expired CSIs and Transferring Their Registered Servers ....................................... 16
1.14.4 Removing a CSI Administrator ........................................................................................ 17
1.15 Switching from RHN to ULN ...................................................................................................... 17
1.16 For More Information About ULN ............................................................................................... 18
This chapter describes how to access and use the software channels that are available on the
Unbreakable Linux Network (ULN).
1.1 About the Unbreakable Linux Network
If you have a subscription to Oracle Unbreakable Linux support, you can use the comprehensive
resources of the Unbreakable Linux Network (ULN). ULN offers software patches, updates, and fixes for
Oracle Linux and Oracle VM, as well as information on yum, Ksplice, and support policies. You can also
download useful packages that are not included in the original distribution. The ULN Alert Notification
Tool periodically checks with ULN and alerts you when updates are available. You can access ULN at
https://linux.oracle.com/, where you will also find instructions for registering with ULN, for creating local yum
repositories, and for switching from the Red Hat Network (RHN) to ULN.
If you want to use yum with ULN to manage your systems, you must register the systems with ULN and
subscribe each system to one or more ULN channels. When you register a system with ULN, the channel
that contains the latest version is chosen automatically according to the architecture and operating system
revision of the system.
When you run yum, it connects to the ULN server repository and downloads the latest software packages
in RPM format onto your system. yum then presents you with a list of the available packages so that you
can choose which ones you want to install.
1.2 About ULN Channels
ULN provides more than 100 unique channels, which support the i386, x86_64, and ia64 architectures, for
releases of Oracle Linux 4 update 6 and later.
7
About ULN Channels
You can choose for your system to remain at a specific OS revision, or you can allow the system to be
updated with packages from later revisions.
You should subscribe to the channel that corresponds to the architecture of your system and the update
level at which you want to maintain it. Patches and errata are available for specific revisions of Oracle
Linux, but you do not need to upgrade from a given revision level to install these fixes. ULN channels also
exist for MySQL, Oracle VM, OCFS2, RDS, and productivity applications.
The following table describes the main channels that are available.
Channel
Description
_latest
Provides all the packages in a distribution, including any errata that are also provided
in the patch channel. Unless you explicitly specify the version, any package that you
download on this channel will be the most recent that is available. If no vulnerabilities
have been found in a package, the package version might be the same as that
included in the original distribution. For other packages, the version will be the same
as that provided in the patch channel for the highest update level. For example, the
ol6_arch_latest channel for Oracle Linux 6 Update 3 contains a combination of
the ol6_u3_arch_base and ol6_u3_arch_patch channels.
_base
Provides the packages for each major version and minor update of Oracle Linux and
Oracle VM. This channel corresponds to the released ISO media image. For example,
there is a base channel for each of the updates to Oracle Linux 6 as well as for Oracle
Linux 6. Oracle does not publish security errata and bugfixes on these channels.
_patch
Provides only those packages that have changed since the initial release of a major or
minor version of Oracle Linux or Oracle VM. The patch channel always provides the most
recent version of a package, including all fixes that have been provided since the initial
version was released.
_addons
Provides packages that are not included in the base distribution, such as the package
that you can use to create a yum repository on Oracle Linux 6.
_oracle
Provides freely downloadable RPMs from Oracle that you can install on Oracle Linux,
such as ASMLib and Oracle Instant Client.
_optional
Provides optional packages for Oracle Linux 7 that have been sourced from upstream.
This channel includes most development packages (*-devel).
Other channels may also be available, such as _beta channels for the beta versions of packages.
As each new major version or minor update of Oracle Linux becomes available, Oracle creates new base
and patch channels for each supported architecture to distribute the new packages. The existing base
and patch channels for the previous versions or updates remain available and do not include the new
packages. The _latest channel distributes the highest possible version of any package, and tracks the
top of the development tree independently of the update level.
Caution
You can choose to maintain your system at a specific update level of Oracle
Linux and selectively apply errata to that level by subscribing the system to the
_base and _patch channels and unsubscribing it from the _latest channel.
However, for Oracle Linux 7, patches are not added to the _patch channel for
previous updates after a new update has been released. For example, after the
release of Oracle Linux 7 Update 1, no further errata will be released on the
ol7_x86_64_u0_patch channel.
8
About Software Errata
Oracle recommends that you keep you system subscribed to the _latest channel.
If you unsubscribe from the _latest channel, your system will become vulnerable
to security-related issues when a new update is released.
1.3 About Software Errata
Oracle releases important changes to Oracle Linux and Oracle VM software as individual package updates
known as errata, which are made available for download on ULN before they are gathered into a release or
are distributed via the _patch channel.
Errata packages can contain:
• Security advisories, which have names prefixed by ELSA-* (for Oracle Linux) and OVMSA-* (for Oracle
VM).
• Bug fix advisories, which have names prefixed by ELBA-* and OVMBA-*.
• Feature enhancement advisories, which have names prefixed by ELEA-* and OVMEA-*.
To be notified when new errata packages are released, you can subscribe to the Oracle Linux and Oracle
VM errata mailing lists at https://oss.oracle.com/mailman/listinfo/el-errata and https://oss.oracle.com/
mailman/listinfo/oraclevm-errata.
If you are logged into ULN, you can also subscribe to these mailing lists by following the Subscribe to
Enterprise Linux Errata mailing list and Subscribe to Oracle VM Errata mailing list links that are
provided on the Errata tab.
1.4 Registering as a ULN User
When you register a system with ULN, your Oracle Single Signon (SSO) user name is also registered as
your ULN user name. If you want to use ULN without first registering a system, you can register as a ULN
user provided that you have a valid customer support identifier (CSI) for Oracle Linux support or Oracle VM
support. To purchase Oracle Linux or Oracle VM support, go to the online Oracle Linux Store or contact
your sales representative.
To register as a ULN user:
1. In a browser, go to https://linux.oracle.com/register.
2. If you do not have an SSO account, click Create New Single Signon Account and follow the onscreen
instructions to create one.
If you already have an SSO account, click Sign On.
3. Log in using your SSO user name and password.
4. On the Create New ULN User page, enter your CSI and click Create New User.
Note
If no administrator is currently assigned to manage the CSI, you are prompted
to click Confirm to become the CSI administrator. If you click Cancel, you
cannot access the CSI administration feature. See Section 1.14, “About CSI
Administration”.
If your user name already exists on the system, you are prompted to proceed
to ULN by clicking the link Unbreakable Linux Network. If you enter a different
9
Registering an Oracle Linux 6 or Oracle Linux 7 System
CSI from your existing CSIs, your user name is associated with the new CSI in
addition to your existing CSIs.
1.5 Registering an Oracle Linux 6 or Oracle Linux 7 System
To register an Oracle Linux 6 or Oracle Linux 7 system with ULN.
1. Run the uln_register command.
# uln_register
Alternatively, if you use the GNOME graphical user desktop, select System > Administration > ULN
Registration on Oracle Linux 6 or Applications > System Tools > ULN Registration on Oracle Linux
7. You can also register your system with ULN if you configure networking when installing Oracle Linux
6 or Oracle Linux 7.
2. When prompted, enter your ULN user name, password, and customer support identifier (CSI).
3. Enter a name for the system that will allow you to identify it on ULN, and choose whether to upload
hardware and software profile data that allows ULN to select the appropriate packages for the system.
4. If you have an Oracle Linux Premier Support account, you can choose to configure an Oracle Linux
6 or Oracle Linux 7 system that is running a supported kernel to receive kernel updates from Oracle
Ksplice. See Section 3.2, “Registering to Use Ksplice Uptrack”.
The yum-rhn-plugin is enabled and your system is subscribed to the appropriate software channels.
If you use a proxy server for Internet access, see Section 2.2.1, “Configuring Use of a Proxy Server”.
1.6 Registering an Oracle Linux 4 or Oracle Linux 5 System
To register an Oracle Linux 4 or Oracle Linux 5 system with ULN.
1. Import the RPM GPG key.
# rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY
2. Run the text-mode version of the up2date command.
# up2date-nox --register
3. When prompted, enter your ULN user name, password, and CSI.
4. Enter the name of the system that will be displayed on ULN, and choose whether to upload hardware
and software profile data that will allow ULN to select the appropriate packages for your system.
1.7 Configuring an Oracle Linux 5 System to Use yum with ULN
If your Oracle Linux 5 system is registered with ULN, you can use yum instead of up2date to download
and install packages. If you have installed a full update since Oracle Linux 5 Update 6 was released on
January 20, 2010, your system should already be able to use yum with ULN.
To enable yum support:
1. Install yum-rhn-plugin.
# up2date --install yum-rhn-plugin
10
Disabling Package Updates
2. If your organization uses a proxy server as an intermediary for Internet access, specify the
enableProxy and httpProxy settings in /etc/sysconfig/rhn/up2date as shown in this
example.
enableProxy=1
httpProxy=http://proxysvr.yourdom.com:3128
If the proxy server requires authentication, additionally specify the enableProxyAuth, proxyUser,
and proxyPassword settings:
enableProxy=1
enableProxyAuth=1
httpProxy=http://proxysvr.yourdom.com:3128
proxyUser=yumacc
proxyPassword=clydenw
Caution
All yum users require read access to /etc/sysconfig/rhn/up2date. If this
file must be world-readable, do not use a password that is the same as any
user's login password, and especially not root's password.
With the plugin installed, you can immediately start to use yum instead of up2date.
1.8 Disabling Package Updates
To disable package updates by ULN (for example, if you have deleted your system from ULN), edit the /
etc/yum/pluginconf.d/rhnplugin.conf file, and change the value of enabled flag from 1 to 0 in
the [main] section, for example:
[main]
enabled = 0
gpgcheck = 1
To disable updates for particular packages, add an exclude statement to the [main] section of the /
etc/yum.conf file. For example, to exclude updates for VirtualBox and kernel:
exclude=VirtualBox* kernel*
Note
Excluding certain packages from being updated can cause dependency errors for
other packages. Your machine might also become vulnerable to security-related
issues if you do not install the latest updates.
1.9 Subscribing Your System to ULN Channels
If you have registered your system with ULN, you can subscribe the system to the channels that are
available for the level of support associated with the CSI.
To subscribe your system to ULN channels:
1. Log in to http://linux.oracle.com with your ULN user name and password.
2. On the Systems tab, click the link named for the system in the list of registered machines.
3. On the System Details page, click Manage Subscriptions.
4. On the System Summary page, select channels from the list of available or subscribed channels and
click the arrows to move the channels between the lists.
11
Browsing and Downloading Errata Packages
5. When you have finished selecting channels, click Save Subscriptions.
1.10 Browsing and Downloading Errata Packages
You can browse the advisories that are available on ULN, and download the errata RPMs for the supported
combinations of the software release and the system architecture.
To browse the advisories and download errata RPMs:
1. Log in to http://linux.oracle.com with your ULN user name and password.
2. Select the Errata tab.
The Errata page displays a table of the available errata for all releases that are available on ULN.
3. On the Errata page, you can perform the following actions on the displayed errata:
• To sort the table of available errata, click the title of the Type, Severity, Advisory, Systems
Affected, or Release Date column. Click the title again to reverse the order of sorting.
Note
The Systems Affected column shows how many of your systems are
potentially affected by an advisory.
• To display or hide advisories of different types, select or deselect the Bug, Enhancement, and
Security check boxes and click Go.
• To display only advisories for a certain release of Oracle Linux or Oracle VM, select that release from
the Release drop-down list and click Go.
• To search within the table, enter a string in the Search field and click Go.
4. To see more detail about an advisory and to download the RPMs:
a. Click the link for the advisory.
b. On the Errata Detail page for an advisory, you can download the RPMs for the supported releases
and system architectures. The Superseded By Advisory column displays a link to the most recent
advisory (if any) that replaces the advisory you are browsing.
1.11 Downloading Available Errata for a System
You can download a comma-separated values (CSV) report file of the errata that are available for your
system and you can download errata RPMs.
To download a CSV report or the errata RPMs:
1. Log in to http://linux.oracle.com with your ULN user name and password.
2. On the Systems tab, click the link named for the system in the list of registered machines.
The System Details page lists the available errata for the system in the Available Errata table, which
might be split over several pages.
3. To download the CSV report file, click the link Download All Available Errata for this System.
4. To see more detail about an advisory and download the RPMs:
12
Updating System Details
a. Click the link for the advisory.
b. On the System Errata Detail page for an advisory, you can download the RPMs for the affected
releases and system architectures.
1.12 Updating System Details
If you have registered your system with ULN, you can update the details that ULN records for the system.
To update the details for your system:
1. Log in to http://linux.oracle.com with your ULN user name and password.
2. On the Systems tab, click the link named for the system in the list of registered machines.
3. On the System Details page, click Edit.
4. On the Edit System Properties page, you can change the name associated with your system, register it
as a local yum server for your site, or change the CSI with which it is registered.
Note
You cannot change the CSI of a system unless it is registered to your user
name.
5. When you have finished making changes, click Apply Changes.
1.13 Deleting a System
To delete a system that is registered on ULN:
1. Log in to http://linux.oracle.com with your ULN user name and password.
2. On the Systems tab, click the link named for the system in the list of registered machines.
3. On the System Details page, click Delete.
Note
You cannot delete a system unless it is registered to your user name.
4. When prompted to confirm the deletion, click OK.
1.14 About CSI Administration
The CSI administration feature of ULN provides a unified view of all of your organization's CSIs and the
systems that are registered with those CSIs. To be able to manage the registered systems, you must
become an administrator for one or more of your organization's CSIs. To be able to view and change the
details of any system that is not registered to your ULN user name, you must become an administrator for
the CSI under which that system is registered.
If you are registered as a CSI administrator, you can access the CSI Administration tab while logged in to
ULN and perform the following tasks:
• Assign yourself as administrator of a CSI, or assign someone else as administrator of a CSI. See
Section 1.14.1, “Becoming a CSI Administrator”.
13
Becoming a CSI Administrator
• List active CSIs, list the servers that are currently registered with an active CSI, and transfer those
servers to another user or to another CSI. See Section 1.14.2, “Listing Active CSIs and Transferring
Their Registered Servers”.
• List expired CSIs, list the servers that are currently registered with an expired CSI, and transfer those
servers to another user or to another CSI. See Section 1.14.3, “Listing Expired CSIs and Transferring
Their Registered Servers”.
• Remove yourself or someone else as administrator of a CSI. See Section 1.14.4, “Removing a CSI
Administrator”.
1.14.1 Becoming a CSI Administrator
You can become an administrator of a CSI in one of the following ways:
• When you register with ULN, if no administrator is currently assigned to manage the CSI, you are
prompted to click Confirm to become the CSI administrator. If you click Cancel, you cannot access the
CSI administration feature.
• When logged into ULN, if you access the System tab and no administrator is currently assigned to
manage one of the CSIs for which you are registered, you are prompted to choose whether to become
the CSI administrator.
To become a CSI administrator:
1. Click the red link labeled enter the CSI you would like to be the administrator for in this page.
2. On the Add CSI page, verify the CSI and click Confirm.
Note
On the Systems page, the CSIs of all systems that have no assigned
administrator are also shown in red.
• If you are already an administrator of a CSI, you can add yourself as administrator of another CSI
provided that you have registered either a server or your ULN user name with the other CSI.
To assign yourself as administrator of an additional CSI:
1. Log in to ULN and select the CSI Administration tab.
2. On the Managed CSIs page, click Add CSI.
3. On the Assign Administrator page, enter the CSI, and click Add.
4. If there are existing administrators, the page lists these administrators and prompts you to click
Confirm to confirm your request. Each administrator is sent an email to inform them that you have
added yourself as an administrator of the CSI.
• An administrator for a CSI can add you as an administrator for the same CSI.
To assign another administrator to a CSI:
1. Log in to ULN as administrator of the CSI, and select the CSI Administration tab.
2. On the Managed CSIs page, click List Administrators.
3. On the CSI Administrators page, click Assign Administrator.
14
Listing Active CSIs and Transferring Their Registered Servers
4. On the Assign Administrator page in the Select New Administrator list, click the + icon that is next to
the user name of the user that you want to add as an administrator. Their user name is added to the
Administrator box.
5. If you administer more than one CSI, select the CSI that the user will administer from the CSI drop
down list.
6. Click Assign Administrator.
Note
If you want to become the administrator of a CSI but the person to whom it
is registered is no longer with your organization, contact an Oracle support
representative to request that you be made the administrator for the CSI.
1.14.2 Listing Active CSIs and Transferring Their Registered Servers
To list details of the active CSIs for which you are the administrator:
1. Log in to ULN as administrator of the CSI, and select the CSI Administration tab.
2. On the Managed CSIs page in the Select Managed CSI Services pane, select the Active link. The
Managed Active CSI Services pane displays the service details for each active CSI that you administer.
3. Click the View # Server(s) link to display the details of the servers that are registered to an active CSI.
4. On the Registered Servers page, you can transfer one or more systems to another user or to another
CSI that you administer.
Note
If you transfer a system to another user, at least one of the following conditions
must be true:
• His or her user name must be registered to this CSI.
• One or more of the servers, for which they are the owner, must be registered
to this CSI.
• He or she must be an administrator of at least one CSI for which you are also
an administrator.
To transfer systems to another user:
a. Select the Transfer System check boxes for the systems that you want to transfer.
b. Click Transfer Selected Systems to Another Owner.
c. On the Transfer Registered System(s) - Owner page in the Transfer To column, click the red arrow
icon that is next to the user name of the user to whom you want to transfer ownership.
d. On the Confirm Transfer Profile - Owner page, click Apply Changes to confirm the transfer to the
new owner.
To transfer systems to another CSI:
a. Select the Transfer System check boxes for the systems that you want to transfer.
15
Listing Expired CSIs and Transferring Their Registered Servers
b. Click Transfer Selected Systems to Another CSI.
c. On the Transfer Registered System(s) - CSI page in the Transfer To column, click the red arrow
icon that is next to the CSI to which you want to transfer the systems.
d. On the Confirm Transfer Profile - CSI page, click Apply Changes to confirm the transfer to the new
CSI.
1.14.3 Listing Expired CSIs and Transferring Their Registered Servers
To list details of the expired CSIs for which you are the administrator:
1. Log in to ULN as administrator of the CSI, and select the CSI Administration tab.
2. On the Managed CSIs page in the Select Managed CSI Services pane, select the Expired link.
The Managed Expired CSI Services pane displays the service details for each expired CSI that you
administer.
3. Click the View # Server(s) link to display the details of the servers that are registered to an expired
CSI.
4. On the Registered Servers page, you can transfer one or more systems to another user or to another
CSI that you administer.
Note
If you transfer a system to another user, at least one of the following conditions
must be true:
• His or her user name must be registered to this CSI.
• One or more of the servers, for which they are the owner, must be registered
to this CSI.
• He or she must be an administrator of at least one CSI for which you are also
an administrator.
To transfer systems to another user:
a. Select the Transfer System check boxes for the systems that you want to transfer.
b. Click Transfer Selected Systems to Another Owner.
c. On the Transfer Registered System(s) - Owner page in the Transfer To column, click the red arrow
icon that is next to the user name of the user to whom you want to transfer ownership.
d. On the Confirm Transfer Profile - Owner page, click Apply Changes to confirm the transfer to the
new owner.
To transfer systems to another CSI:
a. Select the Transfer System check boxes for the systems that you want to transfer.
b. Click Transfer Selected Systems to Another CSI.
c. On the Transfer Registered System(s) - CSI page in the Transfer To column, click the red arrow
icon that is next to the CSI to which you want to transfer the systems.
16
Removing a CSI Administrator
d. On the Confirm Transfer Profile - CSI page, click Apply Changes to confirm the transfer to the new
CSI.
1.14.4 Removing a CSI Administrator
To remove an administrator who is registered for a CSI:
1. Log in to ULN and select the CSI Administration tab.
2. On the Managed CSIs page, click List Administrators.
3. On the CSI Administrators page in the Delete? column, click the trash can icon that is next to the user
name of the user that you want to remove as administrator for the CSI specified in the same row.
4. When prompted to confirm that you want to revoke administration privileges for the CSI from that user,
click OK.
1.15 Switching from RHN to ULN
Note
This procedure is for a Red Hat Enterprise Linux 6 system. For details of equivalent
procedures for Red Hat Enterprise Linux 3, 4, and 5, see http://linux.oracle.com/
switch.html.
If you have an Oracle Linux 6 system that is registered with the Red Hat Network
(RHN), you can use the uln_register utility to register it as described in
Section 1.5, “Registering an Oracle Linux 6 or Oracle Linux 7 System”.
You must have a ULN account before you can register a system with ULN. You can
create a ULN account at http://linux.oracle.com/register.
To register your system with ULN instead of RHN:
1. Download the uln_register.tgz package from http://linux-update.oracle.com/rpms to a temporary
directory.
If the rhn-setup-gnome package is already installed on your system, also download the
uln_register-gnome.tgz from the same URL.
2. Extract the packages using the following command.
# tar -xzf uln_register.tgz
If the rhn-setup-gnome package is installed on your system, extract the packages from
uln_register-gnome.tgz.
# tar -xzf uln_register-gnome.tgz
3. Change to the uln_migrate directory and install the registration packages.
# cd ./uln_migrate
# rpm -Uvh *.rpm
4. Run the uln_register command.
# uln_register
17
For More Information About ULN
5. Follow the instructions on the screen to complete the registration. The uln_register utility collects
information about your system and uploads it to Oracle.
1.16 For More Information About ULN
You can find out more information about ULN at https://linux.oracle.com/.
18
Chapter 2 Yum
Table of Contents
2.1 About Yum ................................................................................................................................. 19
2.2 Yum Configuration ...................................................................................................................... 19
2.2.1 Configuring Use of a Proxy Server ................................................................................... 20
2.2.2 Yum Repository Configuration .......................................................................................... 21
2.3 Downloading the Oracle Public Yum Repository Files ................................................................... 21
2.4 Using Yum from the Command Line ............................................................................................ 22
2.5 Yum Groups ............................................................................................................................... 23
2.6 Installing and Using the Yum Security Plugin ............................................................................... 23
2.7 Switching CentOS or Scientific Linux Systems to Use the Oracle Public Yum Server ...................... 26
2.8 Creating and Using a Local ULN Mirror ....................................................................................... 26
2.8.1 Prerequisites for the Local ULN Mirror .............................................................................. 26
2.8.2 Setting up a Local ULN Mirror .......................................................................................... 27
2.8.3 ULN Mirror Configuration .................................................................................................. 30
2.8.4 Updating the Repositories on a Local ULN Mirror .............................................................. 30
2.8.5 Configuring yum on a Local ULN Mirror ............................................................................ 31
2.8.6 Configuring Oracle Linux Yum Clients of a Local ULN Mirror .............................................. 31
2.9 Creating a Local Yum Repository Using an ISO Image ................................................................. 33
2.10 Setting up a Local Yum Server Using an ISO Image .................................................................. 34
2.11 For More Information About Yum ............................................................................................... 35
This chapter describes how you can use the yum utility to install and upgrade software packages.
2.1 About Yum
Oracle Linux provides the yum utility which you can use to install or upgrade RPM packages. The main
benefit of using yum is that it also installs or upgrades any package dependencies. yum downloads the
packages from repositories such as those that are available on the Oracle public yum server, but you can
also set up your own repositories on systems that do not have Internet access.
The Oracle public yum server is a convenient way to install Oracle Linux and Oracle VM packages,
including bug fixes, security fixes and enhancements, rather than installing them from installation media.
You can access the server at http://public-yum.oracle.com/.
You can also subscribe to the Oracle Linux and Oracle VM errata mailing lists to be notified when new
packages are released. You can access the mailing lists at https://oss.oracle.com/mailman/listinfo/el-errata
and https://oss.oracle.com/mailman/listinfo/oraclevm-errata.
If you have registered your system with the Unbreakable Linux Network (ULN), you can use yum with ULN
channels to maintain the software on your system, as described in Chapter 1, The Unbreakable Linux
Network.
2.2 Yum Configuration
The main configuration file for yum is /etc/yum.conf. The global definitions for yum are located under
the [main] section heading of the yum configuration file. The following table lists the important directives.
Directive
Description
cachedir
Directory used to store downloaded packages.
19
Configuring Use of a Proxy Server
Directive
Description
debuglevel
Logging level, from 0 (none) to 10 (all).
exactarch
If set to 1, only update packages for the correct architecture.
exclude
A space separated list of packages to exclude from installs or updates, for
example: exclude=VirtualBox-4.? kernel*.
gpgcheck
If set to 1, verify the authenticity of the packages by checking the GPG
signatures. You might need to set gpgcheck to 0 if a package is unsigned, but
you should be wary that the package could have been maliciously altered.
gpgkey
Pathname of the GPG public key file.
installonly_limit
Maximum number of versions that can be installed of any one package.
keepcache
If set to 0, remove packages after installation.
logfile
Pathname of the yum log file.
obsoletes
If set to 1, replace obsolete packages during upgrades.
plugins
If set to 1, enable plugins that extend the functionality of yum.
proxy
URL of a proxy server including the port number. See Section 2.2.1,
“Configuring Use of a Proxy Server”.
proxy_password
Password for authentication with a proxy server.
proxy_username
User name for authentication with a proxy server.
reposdir
Directories where yum should look for repository files with a .repo extension.
The default directory is /etc/yum.repos.d.
See the yum.conf(5) manual page for more information.
The following listing shows an example [main] section from the yum configuration file.
[main]
cachedir=/var/cache/yum
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgkey=file://media/RPM-GPG-KEY
gpgcheck=1
pligins=1
installonly_limit=3
It is possible to define repositories below the [main] section in /etc/yum.conf or in separate repository
configuration files. By default, yum expects any repository configuration files to be located in the /etc/
yum.repos.d directory unless you use the reposdir directive to define alternate directories.
2.2.1 Configuring Use of a Proxy Server
If your organization uses a proxy server as an intermediary for Internet access, specify the proxy setting
in /etc/yum.conf as shown in the following example.
proxy=http://proxysvr.yourdom.com:3128
If the proxy server requires authentication, additionally specify the proxy_username, and
proxy_password settings.
proxy=http://proxysvr.yourdom.com:3128
proxy_username=yumacc
20
Yum Repository Configuration
proxy_password=clydenw
If you use the yum plugin (yum-rhn-plugin) to access the ULN, specify the enableProxy and
httpProxy settings in /etc/sysconfig/rhn/up2date as shown in this example.
enableProxy=1
httpProxy=http://proxysvr.yourdom.com:3128
If the proxy server requires authentication, additionally specify the enableProxyAuth, proxyUser, and
proxyPassword settings.
enableProxy=1
httpProxy=http://proxysvr.yourdom.com:3128
enableProxyAuth=1
proxyUser=yumacc
proxyPassword=clydenw
Caution
All yum users require read access to /etc/yum.conf or /etc/sysconfig/rhn/
up2date. If these files must be world-readable, do not use a proxy password that is
the same as any user's login password, and especially not root's password.
2.2.2 Yum Repository Configuration
The yum configuration file or yum repository configuration files can contain one or more sections that
define repositories.
The following table lists the basic directives for a repository.
Directive
Description
baseurl
Location of the repository channel (expressed as a file://, ftp://,
http://, or https:// address). This directive must be specified.
enabled
If set to 1, permit yum to use the channel.
name
Descriptive name for the repository channel. This directive must be specified.
Any other directive that appears in this section overrides the corresponding global definition in [main]
section of the yum configuration file. See the yum.conf(5) manual page for more information.
The following listing shows an example repository section from a configuration file.
[ol6_u2_base]
name=Oracle Linux 6 U2 - $basearch - base
baseurl=http://public-yum.oracle.com/repo/OracleLinux/OL6/2/base/$basearch
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
In this example, the values of gpgkey and gpgcheck override any global setting. yum substitutes the
name of the current system's architecture for the variable $basearch.
2.3 Downloading the Oracle Public Yum Repository Files
Note
The following procedure assumes that yum on your system is configured to expect
to find repository files in the default /etc/yum.repos.d directory.
To download the Oracle public yum repository configuration file:
21
Using Yum from the Command Line
1. As root, change directory to /etc/yum.repos.d.
# cd /etc/yum.repos.d
2. Use the wget utility to download the repository configuration file that is appropriate for your system.
# wget http://public-yum.oracle.com/public-yum-release.repo
For Oracle Linux 6, enter:
# wget http://public-yum.oracle.com/public-yum-ol6.repo
The /etc/yum.repos.d directory is updated with the repository configuration file, in this example,
public-yum-ol6.repo.
3. You can enable or disable repositories in the file by setting the value of the enabled directive to 1 or 0
as required.
2.4 Using Yum from the Command Line
The following table shows some examples of common tasks that you can perform using yum.
Command
Description
yum repolist
Lists all enabled repositories.
yum list
Lists all packages that are available in all enabled repositories and
all packages that are installed on your system.
yum list installed
Lists all packages that are installed on your system.
yum list available
Lists all packages that are available to be installed in all enabled
repositories.
yum search string
Searches the package descriptions for the specified string.
yum provides feature
Finds the name of the package to which the specified file or feature
belongs. For example:
yum provides /etc/sysconfig/atd
yum info package
Displays detailed information about a package. For example:
yum info bind
yum install package
Installs the specified package, including packages on which it
depends. For example:
yum install ocfs2-tools
yum check-update
Checks whether updates exist for packages that are already
installed on your system.
yum update package
Updates the specified package, including packages on which it
depends. For example:
yum upgrade nfs-utils
yum update
Updates all packages, including packages on which they depend.
yum remove package
Removes the specified package. For example:
yum erase nfs-utils
22
Yum Groups
Command
Description
yum erase package
Removes the specified package. This command has the same
effect as the yum remove command.
yum update
Updates all packages, including packages on which they depend.
yum clean all
Removes all cached package downloads and cached headers
that contain information about remote packages. Running
this command can help to clear problems that can result from
unfinished transactions or out-of-date headers.
yum help
Displays help about yum usage.
yum help command
Displays help about the specified yum command. For example:
yum help upgrade
Runs the yum interactive shell.
yum shell
See the yum(8) manual page for more information.
To list the files in a package, use the repoquery utility, which is included in the yum-utils package. For
example, the following command lists the files that the btrfs-progs package provides.
# repoquery -l btrfs-progs
/sbin/btrfs
/sbin/btrfs-convert
/sbin/btrfs-debug-tree
.
.
.
Note
yum makes no distinction between installing and upgrading a kernel package.
yum always installs a new kernel regardless of whether you specify update or
install.
2.5 Yum Groups
A set of packages can themselves be organized as a yum group. Examples include the groups for Eclipse,
fonts, and system administration tools. The following table shows the yum commands that you can use to
manage these groups.
Command
Description
yum grouplist
Lists installed groups and groups that are available for installation.
yum groupinfo groupname
Displays detailed information about a group.
yum groupinstall groupname
Installs all the packages in a group.
yum groupupdate groupname
Updates all the packages in a group.
yum groupremove groupname
Removes all the packages in a group.
2.6 Installing and Using the Yum Security Plugin
The yum-plugin-security package allows you to use yum to obtain a list of all of the errata that are
available for your system, including security updates. You can also use Oracle Enterprise Manager 12c
Cloud Control or management tools such as Katello, Pulp, Red Hat Satellite, Spacewalk, and SUSE
Manager to extract and display information about errata.
23
Installing and Using the Yum Security Plugin
To install the yum-plugin-security package, enter the following command:
# yum install yum-plugin-security
To list the errata that are available for your system, enter:
# yum updateinfo list
Loaded plugins: refresh-packagekit, rhnplugin, security
ELBA-2012-1518 bugfix
NetworkManager-1:0.8.1-34.el6_3.x86_64
ELBA-2012-1518 bugfix
NetworkManager-glib-1:0.8.1-34.el6_3.x86_64
ELBA-2012-1518 bugfix
NetworkManager-gnome-1:0.8.1-34.el6_3.x86_64
ELBA-2012-1457 bugfix
ORBit2-2.14.17-3.2.el6_3.x86_64
ELBA-2012-1457 bugfix
ORBit2-devel-2.14.17-3.2.el6_3.x86_64
ELSA-2013-0215 Important/Sec. abrt-2.0.8-6.0.1.el6_3.2.x86_64
ELSA-2013-0215 Important/Sec. abrt-addon-ccpp-2.0.8-6.0.1.el6_3.2.x86_64
ELSA-2013-0215 Important/Sec. abrt-addon-kerneloops-2.0.8-6.0.1.el6_3.2.x86_64
ELSA-2013-0215 Important/Sec. abrt-addon-python-2.0.8-6.0.1.el6_3.2.x86_64
ELSA-2013-0215 Important/Sec. abrt-cli-2.0.8-6.0.1.el6_3.2.x86_64
ELSA-2013-0215 Important/Sec. abrt-desktop-2.0.8-6.0.1.el6_3.2.x86_64
...
The output from the command sorts the available errata in order of their IDs, and it also specifies whether
each erratum is a security patch (severity/Sec.), a bug fix (bugfix), or a feature enhancement
(enhancement). Security patches are listed by their severity: Important, Moderate, or Low.
You can use the --sec-severity option to filter the security errata by severity, for example:
# yum updateinfo list --sec-severity=Moderate
Loaded plugins: refresh-packagekit, rhnplugin, security
ELSA-2013-0269 Moderate/Sec. axis-1.2.1-7.3.el6_3.noarch
ELSA-2013-0668 Moderate/Sec. boost-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-date-time-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-devel-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-filesystem-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-graph-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-iostreams-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-program-options-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-python-1.41.0-15.el6_4.x86_64
...
To list the security errata by their Common Vulnerabilities and Exposures (CVE) IDs instead of their errata
IDs, specify the keyword cves as an argument:
# yum updateinfo list cves
Loaded plugins: refresh-packagekit, rhnplugin, security
CVE-2012-5659 Important/Sec. abrt-2.0.8-6.0.1.el6_3.2.x86_64
CVE-2012-5660 Important/Sec. abrt-2.0.8-6.0.1.el6_3.2.x86_64
CVE-2012-5659 Important/Sec. abrt-addon-ccpp-2.0.8-6.0.1.el6_3.2.x86_64
CVE-2012-5660 Important/Sec. abrt-addon-ccpp-2.0.8-6.0.1.el6_3.2.x86_64
CVE-2012-5659 Important/Sec. abrt-addon-kerneloops-2.0.8-6.0.1.el6_3.2.x86_64
CVE-2012-5660 Important/Sec. abrt-addon-kerneloops-2.0.8-6.0.1.el6_3.2.x86_64
CVE-2012-5659 Important/Sec. abrt-addon-python-2.0.8-6.0.1.el6_3.2.x86_64
CVE-2012-5660 Important/Sec. abrt-addon-python-2.0.8-6.0.1.el6_3.2.x86_64
...
Similarly, the keywords bugfix, enhancement, and security filter the list for all bug fixes,
enhancements, and security errata.
You can use the --cve option to display the errata that correspond to a specified CVE, for example:
# yum updateinfo list --cve CVE-2012-2677
Loaded plugins: refresh-packagekit, rhnplugin, security
ELSA-2013-0668 Moderate/Sec. boost-1.41.0-15.el6_4.x86_64
ELSA-2013-0668 Moderate/Sec. boost-date-time-1.41.0-15.el6_4.x86_64
24
Installing and Using the Yum Security Plugin
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
ELSA-2013-0668 Moderate/Sec.
updateinfo list done
boost-devel-1.41.0-15.el6_4.x86_64
boost-filesystem-1.41.0-15.el6_4.x86_64
boost-graph-1.41.0-15.el6_4.x86_64
boost-iostreams-1.41.0-15.el6_4.x86_64
boost-program-options-1.41.0-15.el6_4.x86_64
boost-python-1.41.0-15.el6_4.x86_64
boost-regex-1.41.0-15.el6_4.x86_64
boost-serialization-1.41.0-15.el6_4.x86_64
boost-signals-1.41.0-15.el6_4.x86_64
boost-system-1.41.0-15.el6_4.x86_64
boost-test-1.41.0-15.el6_4.x86_64
boost-thread-1.41.0-15.el6_4.x86_64
boost-wave-1.41.0-15.el6_4.x86_64
To display more information, specify info instead of list, for example:
# yum updateinfo info --cve CVE-2012-2677
Loaded plugins: refresh-packagekit, rhnplugin, security
===============================================================================
boost security update
===============================================================================
Update ID : ELSA-2013-0668
Release : Oracle Linux 6
Type : security
Status : final
Issued : 2013-03-21
CVEs : CVE-2012-2677
Description : [1.41.0-15]
: - Add in explicit dependences between some boost
:
subpackages
:
: [1.41.0-14]
: - Build with -fno-strict-aliasing
:
: [1.41.0-13]
: - In Boost.Pool, be careful not to overflow
:
allocated chunk size (boost-1.41.0-pool.patch)
:
: [1.41.0-12]
: - Add an upstream patch that fixes computation of
:
CRC in zlib streams.
: - Resolves: #707624
Severity : Moderate
updateinfo info done
To update all packages for which security-related errata are available to the latest versions of the
packages, even if those packages include bug fixes or new features but not security errata, enter:
# yum --security update
To update all packages to the latest versions that contain security errata, ignoring any newer packages that
do not contain security errata, enter:
# yum --security update-minimal
To update all kernel packages to the latest versions that contain security errata, enter:
# yum --security update-minimal kernel*
You can also update only those packages that correspond to a CVE or erratum, for example:
# yum update --cve CVE-2012-3954
# yum update --advisory ELSA-2012-1141
25
Switching CentOS or Scientific Linux Systems to Use the Oracle Public Yum Server
Note
Some updates might require you to reboot the system. By default, the boot
manager will automatically enable the most recent kernel version.
For more information, see the yum-security(8) manual page.
2.7 Switching CentOS or Scientific Linux Systems to Use the Oracle
Public Yum Server
You can use the centos2ol.sh script to convert CentOS 5 and 6 or Scientific Linux 5 and 6 systems to
Oracle Linux. The script configures yum to use the Oracle's public yum server and installs a few additional
packages that are required. There is no need to reboot the system.
To perform the switch to Oracle Linux, run the following commands as root:
# curl -O https://linux.oracle.com/switch/centos2ol.sh
# sh centos2ol.sh
For more information, see https://linux.oracle.com/switch/centos/.
2.8 Creating and Using a Local ULN Mirror
The following sections describe how to create and use a yum server that acts as a local mirror of the ULN
channels.
2.8.1 Prerequisites for the Local ULN Mirror
The system that you want to set up as a local ULN mirror must meet the following criteria:
• You must have registered the system with ULN. See The Unbreakable Linux Network.
• The system must be running Oracle Linux 5, Oracle Linux 6, or Oracle Linux 7.
• The system must have a least 6 GB of memory to create the yum metadata.
• The system must have enough disk space to store copies of the packages that it hosts. The following
table shows the approximate amount of space that is required for Oracle Linux channels:
Oracle Linux Channel
Space Required per Channel
for Binaries Only
Space Required per Channel
for Both Binaries and Source
[oe]l*_latest
Up to 10 GB
Up to 15 GB
[oe]l*_addons
600 MB
1 GB
[oe]l*_oracle
1 GB
Not applicable
[oe]l*_base
3 GB
5.5 GB
[oe]l*_patch
1 GB
2 GB
The next table shows the approximate amount of space that is required for Oracle VM channels:
Oracle VM Channel
Space Required per Channel
for Binaries Only
Space Required per Channel
for Both Binaries and Source
ovm*_latest
500 MB
1 GB
ovm*_base
400 MB
800 MB
ovm*_patch
100 MB
200 MB
26
Setting up a Local ULN Mirror
2.8.2 Setting up a Local ULN Mirror
To set up a local system as a local ULN mirror:
1. Using a browser, log in at http://linux.oracle.com with the ULN user name and password that you used
to register the system, and configure its properties on ULN as follows:
a. On the Systems tab, click the link named for your system in the list of registered machines.
b. On the System Details page, click Edit.
c. On the Edit System Properties page, select the Yum Server check box and click Apply Changes.
d. On the System Details page, click Manage Subscriptions.
e. On the System Summary page, select channels from the list of available or subscribed channels
and click the arrows to move the channels between the lists.
Modify the list of subscribed channels to include the channels that you want to make available to
local systems.
Note
You must subscribe the system to the latest and addons channels for the
installed operating system release (Oracle Linux 5, Oracle Linux 6, or Oracle
Linux 7) and the system architecture (i386 or x86-64) to be able to install the
yum-uln_mirror package. This package contains the uln-yum-mirror
script that enables the system to act as a local ULN mirror.
For example, the following table shows some examples of the channels that are available for Oracle
Linux 6 on the x86_64 architecture.
Channel
Description
ol6_ga_x86_64_base
All packages for Oracle Linux 6 as initially released. This channel
does not include errata.
ol6_x86_64_addons
Oracle Linux 6 add ons, including the yum-uln_mirror
package.
ol6_x86_64_ksplice
Oracle Ksplice clients, updates, and dependencies for Oracle
Linux 6. Note that access to this channel requires an Oracle
Linux Premier Support account.
ol6_x86_64_latest
All packages released for Oracle Linux 6, including the latest
errata packages.
ol6_x86_64_UEK_latest
Latest Unbreakable Enterprise Kernel Release 2 packages for
Oracle Linux 6.
ol6_x86_64_UEKR3_latest Latest Unbreakable Enterprise Kernel Release 3 packages for
Oracle Linux 6.
If you subsequently update the list of channels to which the system is subscribed, the uln-yummirror script updates the channels that the system mirrors. If you want to be able to use yum to
update the server from the repositories that it hosts rather than from ULN, follow the procedure in
Section 2.8.5, “Configuring yum on a Local ULN Mirror”.
27
Setting up a Local ULN Mirror
If you have an Oracle Linux Premier Support account and you want the yum server to host Ksplice
packages for local Ksplice offline clients, subscribe to the Ksplice for Oracle Linux channels for the
architectures and Oracle Linux releases that you want to support.
For a complete and up-to-date list of the available release channels, log on to ULN at http://
linux.oracle.com.
f.
When you have finished selecting channels, click Save Subscriptions and log out of ULN.
2. Install the Apache HTTP server.
# yum install httpd
3. Create a base directory for the yum repositories, for example /var/yum or /var/www/html/yum.
# mkdir -p /var/www/html/yum
Note
The yum repository owner must have read and write permissions on this
directory.
4. If you created a base directory for the yum repository that is not under /var/www/html and SELinux
is enabled in enforcing mode on your system:
a. Use the semanage command to define the default file type of the repository root directory hierarchy
as httpd_sys_content_t:
# /usr/sbin/semanage fcontext -a -t httpd_sys_content_t "/var/yum(/.*)?"
b. Use the restorecon command to apply the file type to the entire repository.
# /sbin/restorecon -R -v /var/yum
5. If you created a base directory for the yum repository that is not under /var/www/html, create a
symbolic link in /var/www/html that points to the repository, for example:
# ln -s /var/yum /var/www/html/yum
6. Edit the HTTP server configuration file, /etc/httpd/conf/httpd.conf, as follows:
a. Specify the resolvable domain name of the server in the argument to ServerName.
ServerName server_addr:80
If the server does not have a resolvable domain name, enter its IP address instead.
b. Verify that the setting of the Options directive in the <Directory "/var/www/html"> section
specifies Indexes and FollowSymLinks to allow you to browse the directory hierarchy, for
example:
Options Indexes FollowSymLinks
c. Save your changes to the file.
7. Start the HTTP server, and configure it to start after a reboot.
• On Oracle Linux 5 or Oracle Linux 6, enter the following commands:
28
Setting up a Local ULN Mirror
# service httpd start
# chkconfig httpd on
• On Oracle Linux 7, enter the following commands:
# systemctl start httpd
# systemctl enable httpd
8. If you have enabled a firewall on your system, configure it to allow incoming HTTP connection requests
on TCP port 80.
• On Oracle Linux 5 or Oracle Linux 6, enter the following commands:
# iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
# service iptables save
• On Oracle Linux 7, enter the following commands:
# firewall-cmd --zone=zone --add-port=80/udp
# firewall-cmd --permanent --zone=zone --add-port=80/udp
9. Install the uln-yum-mirror package:
# yum install uln-yum-mirror
This package contains the uln-yum-mirror script that enables the system to act as a local ULN
mirror.
Note
If you have not subscribed the system to the correct Oracle Linux latest
and addons channels for your system, the command fails with the error No
package uln-yum-mirror available.
10. To configure the operation of the /usr/bin/uln-yum-mirror script, edit the /etc/sysconfig/
uln-yum-mirror file.
For example, if the base directory for the yum repositories is not /var/www/html/yum, set the value
of the REP_BASE parameter to the correct base directory:
REP_BASE=/var/yum
Installing the uln-yum-mirror package also configures an anacron job (/etc/cron.daily/ulnyum-mirror) that updates the local yum repositories once every day. You can disable this job by
setting the value of CRON_ENABLED to 0:
CRON_ENABLED=0
For more information about the configuration options in /etc/sysconfig/uln-yum-mirror file, see
Section 2.8.3, “ULN Mirror Configuration”.
The repositories are populated when the anacron job runs the /usr/bin/uln-yum-mirror script.
Alternatively, you can run the script manually at any time to update the repositories. See Section 2.8.4,
“Updating the Repositories on a Local ULN Mirror”.
29
ULN Mirror Configuration
2.8.3 ULN Mirror Configuration
The /etc/sysconfig/uln-yum-mirror file contains the following configuration parameters that affect
the behavior of the /usr/bin/uln-yum-mirror script:
ALL_PKGS
Specifies whether uln-yum-mirror mirrors all versions of every available
package or downloads only the latest version of each package. The default value
of 1 causes uln-yum-mirror to mirror all versions of every available package. A
value of 0 causes uln-yum-mirror to download only the latest version of each
package.
CRON_ENABLED
Specifies whether uln-yum-mirror runs automatically once per day. The default
value of 1 enables uln-yum-mirror to be run automatically as an anacron job.
A value of 0 disables the job. You must run uln-yum-mirror manually to update
the packages.
HARDLINK_RPMS
Specifies whether uln-yum-mirror runs hardlinkpy to create hard links
between identical RPMs after the mirror process finishes. The default value of 1
enables hard linking, which saves storage space. It is not possible to create hard
links across file systems. Set the value to 0 if the repository storage spans more
than one file system.
LOG_OUTPUT
Specifies whether uln-yum-mirror logs its output. The default value of 1
enables logging. A value of 0 disables logging.
REP_BASE
Specifies the base directory for the repositories. The default setting is /var/www/
html/yum. Do not change this setting unless you customize the configuration of
the HTTP server.
REP_EL, REP_ENG,
REP_OL, REP_OVM,
REP_UEK
Specify the names of the repositories. If required, you can configure alternate
names.
REPO_FILE_DIR
Not currently used.
SRC
Specifies whether uln-yum-mirror mirrors source RPMs in addition to binary
RPMs. The default value of 0 prevents uln-yum-mirror from mirroring source
RPMs. A value to 1 causes uln-yum-mirror to mirror source RPMs.
YUM_GLOBAL_CACHE
Specifies the yum global cache directory. The default setting is /var/cache/yum.
Do not change this setting unless you customize the configuration of the HTTP
server.
2.8.4 Updating the Repositories on a Local ULN Mirror
To update the repositories for the subscribed channels immediately without waiting for the anacron job to
run or if you have disabled the job, enter the following command on the local ULN mirror server:
# /usr/bin/uln-yum-mirror
Note
If you have not yet set up the contents of the repositories, it can take many hours to
download all the packages.
30
Configuring yum on a Local ULN Mirror
2.8.5 Configuring yum on a Local ULN Mirror
The following procedure configures the yum command on a server that is acting as a local ULN mirror to
install package updates from itself rather than from ULN. The procedure does not affect the operation of
the uln-yum-mirror script.
To configure a server that is acting as a local ULN Mirror to be able to install updated packages from itself:
1. Use the following command to list the channels that the server is mirroring from ULN:
# yum repolist
Loaded plugins: rhnplugin, security
This system is receiving updates from ULN.
0 packages excluded due to repository protections
repo id
repo name
ol6_addons
Oracle Linux 6 Server Add ons (x86_64)
ol6_x86_64_latest
Oracle Linux 6 Latest (x86_64)
ol6_x86_64_UEKR3_latest
Latest Unbreakable Enterprise Kernel
Release 3 for Oracle Linux 6 (x86_64)
status
112
17,976
41
In this example, the server mirrors the ol6_addons, ol6_x86_64_latest, and
ol6_x86_64_UEKR3_latest channels from ULN.
2. Edit /etc/yum/pluginconf.d/rhnplugin.conf and disable the mirrored channels by adding the
following stanza for each channel:
[repo_id]
enabled=0
For example, to disable the ol6_addons, ol6_x86_64_latest, and ol6_x86_64_UEKR3_latest
channels, you would add the following stanzas:
[ol6_addons]
enabled=0
[ol6_x86_64_latest]
enabled=0
[ol6_x86_64_UEKR3_latest]
enabled=0
Note
If you subsequently subscribe the system to any additional channels on
ULN, you must also disable those channels in /etc/yum/pluginconf.d/
rhnplugin.conf.
3. Configure the server as a yum client as described in Section 2.8.6, “Configuring Oracle Linux Yum
Clients of a Local ULN Mirror”.
2.8.6 Configuring Oracle Linux Yum Clients of a Local ULN Mirror
If you have set up a local ULN mirror, you can configure your local Oracle Linux systems to receive yum
updates from that server.
To configure an Oracle Linux system as a yum client:
1. Import the GPG key:
# rpm --import /usr/share/rhn/RPM-GPG_KEY
31
Configuring Oracle Linux Yum Clients of a Local ULN Mirror
2. In the /etc/yum.repos.d directory, edit the existing repository file, such as public-yumol6.repo or ULN-base.repo, and disable all entries by setting enabled=0.
3. In the /etc/yum.repos.d directory, create the file local-yum.repo, which contains entries such
as the following for an Oracle Linux 6 yum client:
[local_ol6_latest]
name=Oracle Linux $releasever - $basearch - latest
baseurl=http://local_uln_mirror/yum/OracleLinux/OL6/latest/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
[local_ol6_UEKR3_latest]
name=Unbreakable Enterprise Kernel Release 3 for Oracle Linux $releasever - $basearch - latest
baseurl=http://local_uln_mirror/yum/OracleLinux/OL6/UEKR3/latest/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
[local_ol6_addons]
name=Oracle Linux $releasever - $basearch - addons
baseurl=http://local_uln_mirror/yum/OracleLinux/OL6/addons/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
To distinguish the local repositories from the ULN repositories, prefix the names of their entries with a
string such as local_.
Replace local_uln_mirror with the IP address or resolvable host name of the local ULN mirror.
The example configuration enables the local_ol6_latest, local_ol6_UEKR3_latest, and
local_ol6_addons channels.
4. To test the configuration:
a. Clear the yum metadata cache:
# yum clean metadata
b. Use yum repolist to verify the configuration, for example:
# yum repolist
Loaded plugins: rhnplugin, security
This system is receiving updates from ULN.
0 packages excluded due to repository protections
repo id
repo name
local_ol6_addons
Oracle Linux 6 - x86_64 - latest
local_ol6_x86_64_latest
Oracle Linux 6 - x86_64 - latest
local_ol6_x86_64_UEKR3_latest
Unbreakable Enterprise Kernel Release 3
for Oracle Linux 6 - x86_64 - latest
status
112
17,976
41
If yum cannot connect to the local ULN mirror, check that the firewall settings on the local ULN
mirror server allow incoming TCP connections to the HTTP port (usually, port 80).
5. You can now run yum update to pick up new updates from the local ULN mirror.
32
Creating a Local Yum Repository Using an ISO Image
2.9 Creating a Local Yum Repository Using an ISO Image
Note
The system must have sufficient storage space to host a full Oracle Linux Media
Pack DVD image (approximately 3.5 GB for Oracle Linux Release 6 Update 3).
To create a local yum repository (for example, if a system does not have Internet access):
1. On a system with Internet access, download a full Oracle Linux DVD image from the Oracle Software
Delivery Cloud at http://edelivery.oracle.com/linux onto removable storage (such as a USB memory
stick). For example, V33411-01.iso contains the Oracle Linux Release 6 Update 3 Media Pack for
x86 (64 bit).
Note
You can verify that the ISO was copied correctly by comparing its checksum
with the digest value that is listed on edelivery.oracle.com, for example:
# sha1sum V33411-01.iso
7daae91cc0437f6a98a4359ad9706d678a9f19de V33411-01.iso
2. Transfer the removable storage to the system on which you want to create a local yum repository, and
copy the DVD image to a directory in a local file system.
# cp /media/USB_stick/V33411-01.iso /ISOs
3. Create a suitable mount point, for example /var/OSimage/OL6.3_x86_64, and mount the DVD
image on it.
# mkdir -p /var/OSimage/OL6.3_x86_64
# mount -o loop,ro /ISOs/V33411-01.iso /var/OSimage/OL6.3_x86_64
Note
Include the read-only mount option (ro) to avoid changing the contents of the
ISO by mistake.
4. Create an entry in /etc/fstab so that the system always mounts the DVD image after a reboot.
/ISOs/V33411-01.iso /var/OSimage/OL6.3_x86_64 iso9660 loop,ro 0 0
5. In the /etc/yum.repos.d directory, edit the existing repository files, such as public-yumol6.repo or ULN-base.repo, and disable all entries by setting enabled=0.
6. Create the following entries in a new repository file (for example, /etc/yum.repos.d/OL63.repo).
[OL63]
name=Oracle Linux 6.3 x86_64
baseurl=file:///var/OSimage/OL6.3_x86_64
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
7. Clean up the yum cache.
# yum clean all
8. Test that you can use yum to access the repository.
# yum repolist
33
Setting up a Local Yum Server Using an ISO Image
Loaded plugins: refresh-packagekit, security
...
repo id
repo name
OL63
Oracle Linux 6.3 x86_64
repolist: 25,459
status
25,459
2.10 Setting up a Local Yum Server Using an ISO Image
To set up a local yum server (for example, if you have a network of systems that do not have Internet
access):
1. Choose one of the systems to be the yum server, and create a local yum repository on it as described
in Section 2.9, “Creating a Local Yum Repository Using an ISO Image”.
2. Install the Apache HTTP server from the local yum repository.
# yum install httpd
3. If SELinux is enabled in enforcing mode on your system:
a. Use the semanage command to define the default file type of the repository root directory hierarchy
as httpd_sys_content_t:
# /usr/sbin/semanage fcontext -a -t httpd_sys_content_t "/var/OSimage(/.*)?"
b. Use the restorecon command to apply the file type to the entire repository.
# /sbin/restorecon -R -v /var/OSimage
Note
The semanage and restorecon commands are provided by the
policycoreutils-python and policycoreutils packages.
4. Create a symbolic link in /var/www/html that points to the repository:
# ln -s /var/OSimage /var/www/html/OSimage
5. Edit the HTTP server configuration file, /etc/httpd/conf/httpd.conf, as follows:
a. Specify the resolvable domain name of the server in the argument to ServerName.
ServerName server_addr:80
If the server does not have a resolvable domain name, enter its IP address instead.
b. Verify that the setting of the Options directive in the <Directory "/var/www/html"> section
specifies Indexes and FollowSymLinks to allow you to browse the directory hierarchy, for
example:
Options Indexes FollowSymLinks
c. Save your changes to the file.
6. Start the Apache HTTP server, and configure it to start after a reboot.
# service httpd start
# chkconfig httpd on
7. If you have enabled a firewall on your system, configure it to allow incoming HTTP connection requests
on TCP port 80.
34
For More Information About Yum
For example, the following command configures iptables to allow incoming HTTP connection
requests and saves the change to the firewall configuration:
# iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
# service iptables save
8. Edit the repository file on the server (for example, /etc/yum.repos.d/OL63.repo):
[OL63]
name=Oracle Linux 6.3 x86_64
baseurl=http://server_addr/OSimage/OL6.3_x86_64
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
Replace server_addr with the IP address or resolvable host name of the local yum server.
9. On each client, copy the repository file from the server to the /etc/yum.repos.d directory.
10. In the /etc/yum.repos.d directory, edit any other repository files, such as public-yum-ol6.repo
or ULN-base.repo, and disable all entries by setting enabled=0.
11. On the server and each client, test that you can use yum to access the repository.
# yum repolist
Loaded plugins: refresh-packagekit, security
...
repo id
repo name
OL63
Oracle Linux 6.3 x86_64
repolist: 25,459
status
25,459
2.11 For More Information About Yum
For more information about yum, see http://yum.baseurl.org/.
For more information about how to download the latest packages from the Unbreakable Linux Network and
make the packages available through a local yum server, see http://www.oracle.com/technetwork/articles/
servers-storage-admin/yum-repo-setup-1659167.html.
35
36
Chapter 3 Ksplice Uptrack
Table of Contents
3.1 About Ksplice Uptrack .................................................................................................................
3.1.1 Supported Kernels ...........................................................................................................
3.2 Registering to Use Ksplice Uptrack .............................................................................................
3.3 Installing Ksplice Uptrack ............................................................................................................
3.4 Configuring Ksplice Uptrack ........................................................................................................
3.5 Managing Ksplice Updates ..........................................................................................................
3.6 Patching and Updating Your System ...........................................................................................
3.7 Removing the Ksplice Uptrack software .......................................................................................
3.8 About Ksplice Offline Client .........................................................................................................
3.8.1 Modifying a Local Yum Server to Act as a Ksplice Mirror ...................................................
3.8.2 Configuring Ksplice Offline Clients ....................................................................................
3.9 For More Information About Ksplice Uptrack ................................................................................
37
37
38
38
39
40
41
41
41
41
42
44
This chapter describes how to configure Ksplice Uptrack to update the kernel on a running system.
3.1 About Ksplice Uptrack
Ksplice Uptrack can update a running Linux kernel without requiring an immediate reboot of the system.
You can apply Ksplice updates to both the Unbreakable Enterprise Kernel and the Red Hat Compatible
Kernel. Oracle creates each Ksplice patch from a kernel update that originates from either Oracle or the
Linux kernel community. Ksplice Uptrack allows you to apply the latest kernel security errata for Common
Vulnerabilities and Exposures (CVEs) without halting the system or restarting applications. Ksplice Uptrack
applies the update patches in the background with a negligible impact, usually consisting of a pause of at
most a few milliseconds. Ksplice Uptrack allows you to keep your systems secure and highly available.
You can use Ksplice Uptrack and still upgrade your kernel using your usual mechanism, such as by using
yum.
3.1.1 Supported Kernels
You can use Ksplice Uptrack to bring the following Oracle Linux kernels up to date with the latest important
security and bug fix patches:
• All Oracle Unbreakable Enterprise Kernel versions for Oracle Linux 5 and Oracle Linux 6 starting with
2.6.32-100.28.9 (released March 16, 2011).
• All Oracle Linux 6 kernels starting with the official release.
• All Oracle Linux 5 Red Hat Compatible Kernels starting with Oracle Linux 5.4 (2.6.18-164.el5, released
September 9, 2009).
• All Oracle Linux 5 Red Hat Compatible Kernels with bug fixes added by Oracle starting with Oracle Linux
5.6 (2.6.18-238.0.0.0.1.el5, released January 22, 2011).
To confirm whether a particular kernel is supported, install the Uptrack client on a system that is running
the kernel.
If you have a question about supported kernels, send e-mail to [email protected]
37
Registering to Use Ksplice Uptrack
3.2 Registering to Use Ksplice Uptrack
When you register your systems with ULN, you can opt to use Oracle Ksplice if you have an Oracle Linux
Premier Support account. If you choose to use Ksplice, you can subscribe your systems to the Ksplice for
Oracle Linux channel and install the Ksplice Uptrack software on them. To install the uptrack package
after registration is complete, you can use yum on an Oracle Linux 6 system or up2date on an Oracle
Linux 5 system. The Uptrack client downloads the access key from ULN and automatically configures itself
so that you can immediately begin to use Ksplice Uptrack.
If you already have an account on ULN, you can register your system to use Ksplice Uptrack at http://
linux.oracle.com.
1. From your browser, log in to ULN with your existing user name and password. If your subscription
grants you access to Ksplice, the ULN home page displays the Ksplice Uptrack Registration button.
2. Click Ksplice Uptrack Registration. The screen displays all valid Customer Support Identifiers (CSIs)
for your account.
3. Select the CSI that you want to use and click Register. The screen displays an acknowledgment that a
Ksplice account has been created and that an e-mail containing the Ksplice access key, a temporary
password for Ksplice, and a URL for confirming your registration has been sent to your e-mail account.
4. When you receive the e-mail, open the URL that it contains.
5. Complete the form to confirm your registration, and click Continue.
After registering to use Ksplice Uptrack, you can log in at https://uptrack.ksplice.com using your e-mail
address as your user name, and the temporary password. You must change your password when you first
log in. You can view the status of your registered systems, the patches that have been applied, and the
patches that are available. You can also create access control groups for your registered systems.
3.3 Installing Ksplice Uptrack
If you have an Oracle Linux Premier Support account and you have registered to use Oracle Ksplice, you
can configure your registered systems to use Ksplice Uptrack through the Ksplice for Oracle Linux channel
on ULN by using yum.
The system on which you want to install Ksplice Uptrack must meet the following criteria:
• The system must be registered with ULN.
• The operating system must be Oracle Linux 5 or Oracle Linux 6 with a supported version of either the
Unbreakable Enterprise Kernel or the Red Hat Compatible Kernel installed. You can verify the kernel
version by using the uname -a command. See Section 3.1.1, “Supported Kernels”.
• The kernel that is running currently is assumed to be the one that you want to update. Ksplice Uptrack
applies updates only to the running kernel.
• The system must have access to the Internet.
To install Ksplice Uptrack from ULN:
1. Log in as root on the system.
2. If you use an Internet proxy, configure the HTTP and HTTPS settings for the proxy in the shell.
• For the sh, ksh, or bash shells, use commands such as the following:
# http_proxy=http://proxy_URL:http_port
38
Configuring Ksplice Uptrack
# https_proxy=http://proxy_URL:https_port
# export http_proxy https_proxy
For the csh shell, use commands such as the following:
# setenv http_proxy=http://proxy_URL:http_port
# setenv https_proxy=http://proxy_URL:https_port
3. Using a browser, log in at http://linux.oracle.com with the ULN user name and password that you used
to register the system, and perform the following steps:
a. On the Systems tab, click the link named for your system in the list of registered machines.
b. On the System Details page, click Manage Subscriptions.
c. On the System Summary page, select the Ksplice for Oracle Linux channel for the correct release
and your system's architecture (i386 or x86_64) from the list of available channels and click the
right arrow (>) to move it to the list of subscribed channels.
d. Click Save Subscriptions and log out of the ULN.
4. On your system, use yum to install the uptrack package.
# yum install -y uptrack
The access key for Ksplice Uptrack is retrieved from ULN and added to /etc/uptrack/
uptrack.conf, for example:
[Auth]
accesskey = 0e1859ad8aea14b0b4306349142ce9160353297daee30240dab4d61f4ea4e59b
5. To enable the automatic installation of updates, change the following entry in /etc/uptrack/
uptrack.conf:
autoinstall = no
so that it reads:
autoinstall = yes
For information about configuring Ksplice Uptrack, see Section 3.4, “Configuring Ksplice Uptrack”.
For information about managing Ksplice updates, see Section 3.5, “Managing Ksplice Updates”.
3.4 Configuring Ksplice Uptrack
The configuration file for Ksplice Uptrack is /etc/uptrack/uptrack.conf. You can modify this file
to configure a proxy server, to install updates automatically at boot time, or to check for and apply new
updates automatically.
Ksplice Uptrack communicates with the Uptrack server by connecting to https://
updates.ksplice.com:443. You can either configure your firewall to allow connection via port 443,
or you can configure Ksplice Uptrack to use a proxy server. To configure Ksplice Uptrack to use a proxy
server, set the following entry in /etc/uptrack/uptrack.conf:
https_proxy = https://proxy_URL:https_port
You receive e-mail notification when Ksplice updates are available for your system.
To make Ksplice Uptrack install all updates automatically as they become available, set the following entry:
39
Managing Ksplice Updates
autoinstall = yes
Note
Enabling automatic installation of updates does not automatically update Ksplice
Uptrack itself. Oracle notifies you by e-mail when you can upgrade the Ksplice
Uptrack software using yum.
To install updates automatically at boot time, the following entry must appear in /etc/uptrack/
uptrack.conf:
install_on_reboot = yes
When you boot the system into the same kernel, the /etc/init.d/uptrack script reapplies the installed
Ksplice updates to the kernel.
To prevent Ksplice Uptrack from automatically reapplying updates to the kernel when you reboot the
system, set the entry to:
install_on_reboot = no
To install all available updates at boot time, even if you boot the system into a different kernel, uncomment
the following entry in /etc/uptrack/uptrack.conf:
#upgrade_on_reboot = yes
so that it reads:
upgrade_on_reboot = yes
3.5 Managing Ksplice Updates
Ksplice patches are stored in /var/cache/uptrack. Following a reboot, Ksplice Uptrack automatically
re-applies these patches very early in the boot process before the network is configured, so that the
system is hardened before any remote connections can be established.
To list the available Ksplice updates, use the uptrack-upgrade command:
# uptrack-upgrade -n
To install all available Ksplice updates, enter:
# uptrack-upgrade -y
To install an individual Ksplice update, specify the update's ID as the argument (in this example, the ID is
dfvn0zq8):
# uptrack-upgrade dfvn0zq8
After Ksplice has applied updates to a running kernel, the kernel has an effective version that is different
from the original boot version displayed by the uname –a command. Use the uptrack-uname command
to display the effective version of the kernel:
# uptrack-uname -a
uptrack-uname supports the commonly used uname flags, including -a and -r, and provides a way
for applications to detect that the kernel has been patched. The effective version is based on the version
number of the latest patch that Ksplice Uptrack has applied to the kernel.
To view the updates that Ksplice has made to the running kernel:
# uptrack-show
40
Patching and Updating Your System
To view the updates that are available to be installed:
# uptrack-show --available
To remove all updates from the kernel:
# uptrack-remove --all
To prevent Ksplice Uptrack from reapplying the updates at the next system reboot, create the empty file /
etc/uptrack/disable:
# touch /etc/uptrack/disable
Alternatively, specify nouptrack as a parameter on the boot command line when you next restart the
system.
3.6 Patching and Updating Your System
Ksplice patches allow you to keep a system up to date while it is running. You should also use yum or rpm
to install the regular kernel RPM packages for released errata that are available from the Unbreakable
Linux Network (ULN) or the Oracle Public Yum server. Your system will then be ready for the next
maintenance window or reboot. When you do restart the system, you can boot it from a newer kernel
version. Ksplice Uptrack uses the new kernel as a baseline for applying patches as they become available.
3.7 Removing the Ksplice Uptrack software
To remove the Ksplice Uptrack software from a system, enter:
# yum -y remove uptrack
3.8 About Ksplice Offline Client
Ksplice Offline Client removes the requirement for a server on your intranet to have a direct connection to
the Oracle Uptrack server. All available Ksplice updates for each supported kernel version are bundled into
an RPM that is specific to that version, and this package is updated every time that a new Ksplice patch
becomes available for the kernel.
A Ksplice offline client does not require a network connection to be able to apply the update package to
the kernel. For example, you could use rpm to install the update package from a memory stick. However,
a more usual arrangement would be to create a local yum server that acts as a mirror of the Ksplice for
Oracle Linux channels on ULN. At regular intervals, you download the latest Ksplice update packages to
this server. Only the local yum server requires access the Oracle Uptrack server. After installing Ksplice
Offline Client on your other systems, they need only to be able to connect to the local yum server.
Note
You cannot use the web interface or the Ksplice Uptrack API to monitor systems
that are running Ksplice Offline Client as such systems are not registered with
https://uptrack.ksplice.com.
3.8.1 Modifying a Local Yum Server to Act as a Ksplice Mirror
The system that you want to set up as a Ksplice mirror must meet the following criteria:
• You must have registered the system with ULN.
• You must have configured the system as a local yum server. See Section 2.8, “Creating and Using a
Local ULN Mirror”.
41
Configuring Ksplice Offline Clients
• The system should also have enough disk space to store copies of the packages that it hosts. As a
general rule, you require between 6 and 10 GB of space for the packages of each major release.
To set up a local yum server as a Ksplice mirror:
1. Using a browser, log in at http://linux.oracle.com with the ULN user name and password that you used
to register the system.
2. On the Systems tab, click the link named for your system in the list of registered machines.
3. On the System Details page, click Edit.
4. On the Edit System Properties page, verify that the Yum Server check box is selected and click Apply
Changes.
5. On the System Details page, click Manage Subscriptions.
6. On the System Summary page, select channels from the list of available or subscribed channels and
click the arrows to move the channels between the lists.
Modify the subscribed channels to include Ksplice for Oracle Linux for the system architectures that you
want to support as well as any other channels that you want to make available to local systems.
For example, the following table shows the channels that are available for Ksplice on Oracle Linux.
Channel Name
Channel Label
Description
Ksplice for Oracle
Linux 5 (i386)
ol5_i386_ksplice
Oracle Ksplice clients, updates, and dependencies
for Oracle Linux 5 on i386 systems.
Ksplice for Oracle
Linux 5 (x86_64)
ol5_x86_64_ksplice
Oracle Ksplice clients, updates, and dependencies
for Oracle Linux 5 on x86_64 systems.
Ksplice for Oracle
Linux 6 (i386)
ol6_i386_ksplice
Oracle Ksplice clients, updates, and dependencies
for Oracle Linux 6 on i386 systems.
Ksplice for Oracle
Linux 6 (x86_64)
ol6_x86_64_ksplice
Oracle Ksplice clients, updates, and dependencies
for Oracle Linux 6 on x86_64 systems.
Ksplice for Oracle
Linux 7 (x86_64)
ol7_x86_64_ksplice
Oracle Ksplice clients, updates, and dependencies
for Oracle Linux 7 on x86_64 systems.
For more information about the release channels that are available, see http://www.oracle.com/
technetwork/articles/servers-storage-admin/yum-repo-setup-1659167.html.
7. When you have finished selecting channels, click Save Subscriptions and log out of ULN.
3.8.2 Configuring Ksplice Offline Clients
Once you have set up a local yum server that can act as a Ksplice mirror, you can configure your other
systems to receive yum and Ksplice updates.
To configure a system as a Ksplice offline client:
1. In the /etc/yum.repos.d directory, edit the existing repository file, such as public-yumol6.repo or ULN-base.repo, and disable all entries by setting enabled=0.
2. In the /etc/yum.repos.d directory, create the file local-yum.repo, which contains entries such
as the following for an Oracle Linux 6 client:
[ol6_x86_64_ksplice]
name=Ksplice for $releasever - $basearch
42
Configuring Ksplice Offline Clients
baseurl=http://local_yum_server/yum/OracleLinux/OL6/ksplice/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
[ol6_latest]
name=Oracle Linux $releasever - $basearch - latest
baseurl=http://local_yum_server/yum/OracleLinux/OL6/latest/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=1
[ol6_addons]
name=Oracle Linux $releasever - $basearch - addons
baseurl=http://local_yum_server/yum/OracleLinux/OL6/addons/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_oracle]
name=Oracle Linux $releasever - $basearch - oracle
baseurl=http://local_yum_server/yum/OracleLinux/OL6/oracle/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_ga_base]
name=Oracle Linux $releasever GA - $basearch - base
baseurl=http://local_yum_server/yum/OracleLinux/OL6/0/base/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_u1_base]
name=Oracle Linux $releasever U1 - $basearch - base
baseurl=http://local_yum_server/yum/OracleLinux/OL6/1/base/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_u2_base]
name=Oracle Linux $releasever U2 - $basearch - base
baseurl=http://local_yum_server/yum/OracleLinux/OL6/2/base/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_u3_base]
name=Oracle Linux $releasever U3 - $basearch - base
baseurl=http://local_yum_server/yum/OracleLinux/OL6/3/base/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_ga_patch]
name=Oracle Linux $releasever GA - $basearch - patch
baseurl=http://local_yum_server/yum/OracleLinux/OL6/0/patch/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_u1_patch]
name=Oracle Linux $releasever U1 - $basearch - patch
baseurl=http://local_yum_server/yum/OracleLinux/OL6/1/patch/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
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For More Information About Ksplice Uptrack
[ol6_u2_patch]
name=Oracle Linux $releasever U2 - $basearch - patch
baseurl=http://local_yum_server/yum/OracleLinux/OL6/2/patch/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
[ol6_u3_patch]
name=Oracle Linux $releasever U3 - $basearch - patch
baseurl=http://local_yum_server/yum/OracleLinux/OL6/3/patch/$basearch/
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY
gpgcheck=1
enabled=0
Replace local_yum_server with the IP address or resolvable host name of the local yum server.
In the sample configuration, only the ol6_latest and ol6_x86_64_ksplice channels are enabled.
Note
As an alternative to specifying a gpgkey entry for each repository definition, you
can use the following command to import the GPG key:
# rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY
3. Install the Ksplice offline client.
# yum install uptrack-offline
If yum cannot connect to the local yum server, check that the firewall settings on that server allow
incoming TCP connections to port 80.
4. Install the Ksplice updates that are available for the kernel.
# yum install uptrack-updates-`uname -r`
For an Oracle Linux 5 client, use this form of the command instead:
# yum install uptrack-updates-`uname -r`.`uname -m`
As new Ksplice updates are made available, you can use this command to pick up these updates
and apply them. It is recommended that you set up a cron job to perform this task. For example, the
following crontab entry for root runs the command once per day at 7am:
0 7 * * * yum install uptrack-updates-`uname -r`
To display information about Ksplice updates, use the rpm -qa | grep uptrack-updates and
uptrack-show commands.
3.9 For More Information About Ksplice Uptrack
You can find out more information about Ksplice Uptrack at http://www.ksplice.com/.
44
Chapter 4 Boot Configuration
Table of Contents
4.1 About the Boot Process ..............................................................................................................
4.2 About the GRUB Boot Loader .....................................................................................................
4.2.1 About the GRUB Configuration File ..................................................................................
4.2.2 Configuring a GRUB Password .........................................................................................
4.2.3 Using GRUB ....................................................................................................................
4.3 About Run Levels .......................................................................................................................
4.3.1 Displaying the Run Level .................................................................................................
4.3.2 Changing the Run Level ...................................................................................................
4.3.3 Shutting down the System ................................................................................................
4.3.4 About Service Scripts .......................................................................................................
4.3.5 About the Service Configuration GUI ................................................................................
4.3.6 Starting and Stopping Services .........................................................................................
4.3.7 Configuring Services to Start at Different Run Levels .........................................................
45
46
47
50
51
51
52
52
52
52
53
54
54
This chapter describes the Oracle Linux boot process, how to use the GRUB boot loader, how to change
the run level of a system, and how to configure the services that are available at each run level.
4.1 About the Boot Process
Understanding the Oracle Linux boot process can help you if you need to troubleshoot problems while
booting a system. The boot process involves several files and errors in these files is the usual cause of
boot problems.
When an Oracle Linux system boots, it performs the following operations:
1. The computer's BIOS performs a power-on self-test (POST), and then locates and initializes any
peripheral devices including the hard disk.
2. The BIOS reads the Master Boot Record (MBR) into memory from the boot device. (For GUID Partition
Table (GPT) disks, this MBR is the protective MBR on the first sector of the disk.) The MBR stores
information about the organization of partitions on that device. On a computer with x86 architecture,
the MBR occupies the first 512 bytes of the boot device. The first 446 bytes contain boot code that
points to the bootloader program, which can be on the same device or on another device. The next
64 bytes contain the partition table. The final two bytes are the boot signature, which is used for error
detection. The default bootloader program used on Oracle Linux is GRUB, which stands for GRand
Unified Bootloader.
3. The GRUB bootloader loads the Oracle Linux kernel into memory.
4. The kernel initializes and configures the system hardware.
5. The kernel reads the initramfs file, extracts its contents into a temporary, memory-based file system
(tmpfs), and loads the modules that the file system contains.
6. The kernel starts the /sbin/init process with a process ID of 1 (PID 1). init is the ancestor of all
processes on a system. init reads its job configuration from the /etc/init directory. The /etc/
init/rcS.conf file controls how init handles system initialization.
7. init reads /etc/inittab to determine the default run level. The entry in /etc/inittab should
take the form id:N:initdefault:, where N is the default run level. If the file does not define a
default boot level, the default run level is 3.
45
About the GRUB Boot Loader
Note
Do not edit /etc/inittab other than to change or comment out the default
run level.
The sole function of /etc/inittab is to define the default run level. The
*.conf scripts in /etc/init determine how init should behave in response
to changes in system state.
You can use a kernel boot parameter to override the default run level. See
Section 4.2.1.1, “Kernel Boot Parameters”.
8. init runs /etc/rc.sysinit to initialize the system, including:
• setting the host name
• initializing the network
• mounting the /proc file system
• initializing SELinux based on its configuration
• printing a welcome banner
• initializing the system hardware based on kernel boot arguments
• mounting the file systems
• cleaning up directories in /var
• starting swapping
9. init executes scripts in the /etc/rcX.d directory to bring the system to the default run level, X. The
/etc/init/rc.conf file controls how init starts individual run levels. See Section 4.3, “About Run
Levels” and Section 4.3.4, “About Service Scripts”.
10. init runs any actions that you have defined in /etc/rc.local.
Note
The Upstart version of init in Oracle Linux does not keep track of system run
levels. Instead, user-space utilities such as initctl implement run levels. The
processes that init manages are known as jobs, which are defined by files in the
/etc/init directory. init is an event-based daemon, starting or stopping jobs
in response to changes in the system state, which can be the result of other jobs
starting or stopping.
For information on Upstart and on how to write Upstart event handlers, see the init(5), init(8), and
initctl(8) manual pages.
4.2 About the GRUB Boot Loader
GRUB can load many operating systems in addition to Oracle Linux and it can chain-load proprietary
operating systems. GRUB understands the formats of file systems and kernel executables, which allows
it to load an arbitrary operating system without needing to know the exact location of the kernel on the
boot device. GRUB requires only the file name and drive partitions to load a kernel. You can configure this
46
About the GRUB Configuration File
information by editing the /boot/grub/grub.conf file, by using the GRUB menu, or by entering it on
the command line. A portion of the GRUB bootloader code (stage 1 code) is written to the MBR, and the
remainder is written to the /boot partition.
The GRUB bootloader is modular and operates in the following stages:
Stage 1
Stage 1 code is stored in the MBR. This code contains a block list that points to the next
stage of GRUB, which is either stage1_5 or stage 2, depending on the file system type.
# dd if=/dev/sda count=1 of=/tmp/MBR
1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.000283544 s, 1.8 MB/s
# file /tmp/MBR
/tmp/MBR: x86 boot sector; GRand Unified Bootloader, stage1 version 0x3,
boot drive 0x80, 1st sector stage2 0x8480e, GRUB version 0.94;
partition 1: ID=0x83, active, starthead 32, startsector 2048, 1024000 sectors;
partition 2: ID=0x8e, starthead 221, startsector 1026048, 82860032 sectors,
code offset 0x48
An unamended copy of the stage 1 code can be found in the file /boot/grub/stage1.
# file /boot/grub/stage1
/boot/grub/stage1: x86 boot sector; GRand Unified Bootloader, stage1 version 0x3,
GRUB version 0.94, code offset 0x48
Stage 1_5
Stage1_5 code allows GRUB to interpret different types of file system. For some file system
types such as ext4, GRUB does not need to load stage1_5. The code for each file system
type is stored as files in /boot/grub:
# cd /boot/grub
# ls *stage1_5
e2fs_stage1_5 iso9660_stage1_5
fat_stage1_5
jfs_stage1_5
ffs_stage1_5
minix_stage1_5
Stage 2
reiserfs_stage1_5
ufs2_stage1_5
vstafs_stage1_5
xfs_stage1_5
Stage 2 code reads /boot/grub/grub.conf to determine how to load the kernel. The stage
2 code is stored in the file /boot/grub/stage2:
# ls -al /boot/grub/stage2
-rw-r--r--. 1 root root 125976 Jun 28
2012 /boot/grub/stage2
4.2.1 About the GRUB Configuration File
The GRUB configuration file, /boot/grub/grub.conf, starts with the default, timeout,
splashimage, and hiddenmenu directives:
default
Specifies the kernel entry that GRUB should boot by default. GRUB counts the kernel
entries in the configuration file starting at 0. The directive default=0 means that GRUB
boots the first kernel entry by default, unless you override this action. If you have installed
the Unbreakable Enterprise Kernel, it is configured as the first entry, and the Red Hat
Compatible Kernel is configured as the second entry. Changing the value of default to
1 would cause GRUB to boot the Red Hat Compatible Kernel by default.
timeout
Specifies the number of seconds that GRUB should wait for keyboard input before
booting the default kernel. Pressing any alphanumeric key within this period displays
the GRUB menu. The default timeout is 5 seconds. A value of 0 causes GRUB to boot
the default kernel immediately. A value of -1 or no value at all causes GRUB to wait
indefinitely until you press a key.
47
About the GRUB Configuration File
splashimage
Specifies the splash screen that hides boot messages. Pressing Esc bypasses the splash
screen. The default splash image is (hd0,0)/grub/splash.xpm.gz, which is a
gzipped, xpm-format file.
hiddenmenu
If specified, instructs GRUB not to display the GRUB menu by default unless a key is
pressed.
password
If specified with the arguments --md5 pwhash, specifies the MD5 hash of a GRUB
password generated using the /sbin/grub-md5-crypt command. See Section 4.2.2,
“Configuring a GRUB Password”.
Following these directives are title entries that represent each bootable Oracle Linux kernel or other
operating system partition.
For Linux systems, the title contains a description of the kernel and the kernel version number in
parentheses. Each title is followed by root, kernel, initrd, and optional lock directives, which
should be indented:
lock
If specified, you must enter the correct GRUB password to boot the specified kernel or operating
system. See Section 4.2.2, “Configuring a GRUB Password”.
root
Specifies the root partition, which can be on a local disk or on a SAN-attached disk. The first
hard drive detected by the BIOS is named hd0, the second is named hd1, and so on. The
partitions on a disk are numbered from 0. For example, root (hd0,1) specifies the first
detected disk and the second partition on that disk. The mapping between BIOS-detected disks
and device files is stored in /boot/grub/device.map, for example:
# cat /boot/grub/device.map
# this device map was generated by anaconda
(hd0)
/dev/sda
kernel
Specifies the kernel version to be booted as a path relative to the root of the boot partition,
together with any kernel boot parameters. See Section 4.2.1.1, “Kernel Boot Parameters”.
initrd
Specifies the initramfs file as a path relative to the root of the boot partition. The kernel uses
this file to create the initial root file system that it mounts before the real root file system. The
purpose of the initial root file system is to allow the kernel to preload driver modules for IDE,
SCSI, RAID and other devices, so that it can access and mount the real root file system. After
the newly-loaded kernel has complete access to the real root file system, it switches over to
using it.
initramfs files accompany kernel distributions and usually have the same version number as
the kernel that they support. You would not usually need to change or modify an initramfs file
unless you build a kernel to support a new device driver module.
Note
The name initrd is a legacy of when the initial root file system was
provided as a file system image. The initramfs file is actually a cpio
archive.
The following sample entries are taken from a GRUB configuration file:
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
#
all kernel and initrd paths are relative to /boot/, eg.
#
root (hd0,0)
48
About the GRUB Configuration File
#
kernel /vmlinuz-version ro root=/dev/mapper/VolGroup-lv_root
#
initrd /initrd-[generic-]version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Oracle Linux Server (3.6.39-400.17.1.el6uek.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.39-400.17.1.el6uek.x86_64 ro root=/dev/mapper/VolGroup-lv_root
rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=uk LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap
SYSFONT=latarcyrheb-sun16 rd_LVM_LV=VolGroup/lv_root rd_NO_DM rhgb quiet
initrd /initramfs-2.6.39-400.17.1.el6uek.x86_64.img
title Oracle Linux Server (2.6.32-358.0.1.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-358.0.1.el6.x86_64 ro root=/dev/mapper/VolGroup-lv_root
rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=uk LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap
SYSFONT=latarcyrheb-sun16 rd_LVM_LV=VolGroup/lv_root rd_NO_DM rhgb quiet crashkernel=auto
initrd /initramfs-2.6.32-358.0.1.el6.x86_64.img
In this example, the default kernel is the Unbreakable Enterprise Kernel (3.6.39-400.17.1.el6uek.x86_64)
and the other bootable kernel is the Red Hat Compatible Kernel (2.6.32-358.0.1.el6.x86_64). As this
system has a separate boot partition, the paths of the kernel and initrd files are given relative to the
root of that partition.
4.2.1.1 Kernel Boot Parameters
The following table lists commonly-used kernel boot parameters.
Option
Description
1|2|3|4|5
Specifies the run level, overriding the value set in /
etc/inittab.
KEYBOARDTYPE=kbtype
Specifies the keyboard type, which is written to /
etc/sysconfig/keyboard in the initramfs.
KEYTABLE=kbtype
Specifies the keyboard layout, which is written to /
etc/sysconfig/keyboard in the initramfs.
LANG=language_territory.codeset
Specifies the system language and code set,
which is written to /etc/sysconfig/i18n in the
initramfs.
max_loop=N
Specifies the number of loop devices (/dev/
loop*) that are available for accessing files as
block devices. The default and maximum values of N
are 8 and 255.
nouptrack
Disables Ksplice Uptrack updates from being
applied to the kernel.
quiet
Reduces debugging output.
rd_LUKS_UUID=UUID
Activates an encrypted Linux Unified Key Setup
(LUKS) partition with the specified UUID.
rd_LVM_VG=vg/lv_vol
Specifies an LVM volume group and volume to be
activated.
rd_NO_LUKS
Disables detection of an encrypted LUKS partition.
rhgb
Specifies that the Red Hat graphical boot display
should be used to indicate the progress of booting.
rn_NO_DM
Disables Device-Mapper (DM) RAID detection.
49
Configuring a GRUB Password
Option
Description
rn_NO_MD
Disables Multiple Device (MD) RAID detection.
ro root=/dev/mapper/vg-lv_root
Specifies that the root file system is to be mounted
read only, and specifies the root file system by the
device path of its LVM volume (where vg is the
name of the volume group).
rw root=UUID=UUID
Specifies that the root (/) file system is to be
mounted read-writable at boot time, and specifies
the root partition by its UUID.
selinux=0
Disables SELinux.
single
Boots the computer in single-user mode, without
prompting for the root password.
SYSFONT=font
Specifies the console font, which is written to /etc/
sysconfig/i18n in the initramfs.
The kernel boot parameters that were last used to boot a system are recorded in /proc/cmdline, for
example:
# cat /proc/cmdline
ro root=/dev/mapper/VolGroup-lv_root rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=us
LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap SYSFONT=latarcyrheb-sun16
rd_LVM_LV=VolGroup/lv_root rd_NO_DM rhgb quiet selinux=0
4.2.2 Configuring a GRUB Password
If a system is not kept in a locked data center, and as an alternative to using any password protection
mechanism built into the BIOS, you can add a degree of protection to the system by requiring a valid
password be provided to the GRUB boot loader.
Note
Password protecting GRUB access prevents unauthorized users from entering
single user mode and changing settings at boot time. It does not prevent someone
from accessing data on the hard drive by booting into an operating system from
a memory stick, or physically removing the drive to read its contents on another
system.
To configure a GRUB password:
1. Use the following command to generate the MD5 hash of your password:
# /sbin/grub-md5-crypt
Password: clydenw
Retype password: clydenw
$1$qhqh.1$7MQxS6GHg4IlOFMdnDx9S.
2. Edit /boot/grub/grub.conf, and add a password entry below the timeout entry near the top of
the file, for example:
timeout=5
password --md5 pwhash
where pwhash is the hash value that grub-md5-crypt returned.
3. If GRUB has been configured to boot multiple operating systems on the same machine, add a lock
entry to after the title entry for each operating system, for example:
50
Using GRUB
title Windows
lock
When you reboot the machine, you must press P and enter the GRUB password before you can access the
GRUB command interface.
4.2.3 Using GRUB
Note
All changes that you make at boot time are temporary. GRUB does not update the
configuration file. To make your changes permanent, boot the system, and use a
text editor to modify the entries in /boot/grub/grub.conf.
When booting a system, you can access the GRUB menu by pressing a key before the timeout expires.
GRUB displays the title entries from the /boot/grub/grub.conf file, and highlights the default entry.
You can use the up and down arrow keys to choose a different entry and press Enter to boot it.
If you have set a GRUB password, you must press P and enter the valid password to be able to edit the
titles or change kernel boot parameters. To edit any of the root, kernel, or initrd directives, press E.
To edit the kernel directive only, press A. To use the GRUB command line, press C.
If you press E, select the root, kernel, or initrd directive, and press E to edit it. Initially, the entry
cursor is placed at the end of the directive. Use the Home, End, and left and right arrow keys to move
through the line. Use the Backspace and Delete keys to erase characters, and type in your changes at
the cursor position. Press Enter to save your changes or press Esc to discard them. Press B to start the
boot sequence using the changes that you have made.
If you press A, you can edit the root directive. Initially, the entry cursor is placed at the end of the
directive. Use the Home, End, and left and right arrow keys to move through the line. Use the Backspace
and Delete keys to erase characters, and type in your changes at the cursor position. Press Enter to
save your changes and boot the system or press Esc to discard the changes.
If you press C, you can enter GRUB commands. Enter help to see a list of commands. Enter help
command to see more information about a specified command.
For more information, enter the info grub command to access the GRUB manual.
4.3 About Run Levels
Run levels allow you to start a system with only the services that are required for a specific purpose. For
example, a server can run more efficiently at run level 3, because it does not run the X Window System
at that run level. It is best to perform diagnostics, backups, and upgrades at run level 1 when only root
can use the system. Each run level defines the services that init stops or starts. For example, run level
3 starts network services and run level 5 starts the X Window System, whereas run level 1 stops both of
these services.
The following run levels are defined by default under Oracle Linux:
0
Halts the system.
1
Single-user text mode.
2
Full multiuser text mode without NFS support.
3
Full multiuser text mode with NFS support.
4
Not used, but can be user defined.
51
Displaying the Run Level
5
Full multiuser graphical mode with an X-based login screen.
6
Reboots the system.
4.3.1 Displaying the Run Level
To display the previous and current run level, use the runlevel command, for example:
# runlevel
N 5
If there is no previous run level, N is displayed. In this example, the current run level is 5.
The who -r command also displays the current run level, for example:
# who -r
run-level 5
2013-03-15 09:24
For more information, see the runlevel(8) and who(1) manual pages.
4.3.2 Changing the Run Level
Use the telinit command to change the system run level, for example:
# telinit 1
which place the system in single-user mode.
Tip
telinit 0 halts a system immediately.
telinit 6 reboots a system immediately.
You can also use the init command to change run level. Any instance of init that does not have a
process ID of 1 invokes telinit to change the run level.
For more information, see the telinit(8) manual page.
4.3.3 Shutting down the System
Although you can use telinit to halt and reboot a system, the shutdown command is preferred as it
notifies all logged-in users of the impending action.
For example, to shutdown a system in 5 minutes time and then reboot it:
# shutdown –r 5
The system is going down for reboot in 5 minutes!
To shutdown a system immediately:
# shutdown –h now
For more information, see the shutdown(8) manual page.
4.3.4 About Service Scripts
The /etc/init.d directory contains the scripts that are used to start, stop, or otherwise control the
operation of system services. When the system changes run level, init, under the control of the /etc/
init/rc.conf file, calls the /etc/rc script to start the services that are required for the new run level
and to stop any currently running services that are not required.
52
About the Service Configuration GUI
For each run level N, there is an /etc/rcN.d directory that contains the scripts that init uses to start
and stop services. For example, /etc/rc3.d is the directory for run level 3. Each script in an /etc/
rcN.d directory is actually a symbolic link to a script in /etc/init.d. Using symbolic links allows you to
reconfigure run levels without affecting the scripts that the symbolic links reference.
The name of each symbolic link begins with either K (for kill) or S (for start), followed by a sequence
number that indicates the order in which init should kill or start the services. init first stops each of the
K* services in the order of their sequence numbers by executing each K script with the argument stop.
init then starts each of the S* services in the order of their sequence numbers by executing each S script
with the argument start. If symbolic links have the same sequence number, init stops or starts them in
alphabetic order.
Note
The entries for init.d, rc, rc.local, rc.sysinit, and rcN.d in /etc are
actually symbolic links to entries in the /etc/rc.d directory. These links ensure
compatibility with UNIX System V (SysV).
To customize service initialization, you can add scripts to /etc/init.d and create symbolic links to these
scripts in the /etc/rcN.d directories, naming the links with an initial K or S according to whether init
should stop or start the service in each run level N.
Alternatively, you can add commands to the /etc/rc.local script to start services or initialize devices.
For more information on writing SysV init scripts, see /usr/share/doc/initscripts*/
sysvinitfiles.
4.3.5 About the Service Configuration GUI
You can use the Service Configuration GUI (system-config-services) to start, stop, and restart a
service, to enable or disable the system from running the service, and to customize the run levels at which
the system runs the service. Alternatively, you can use commands such as service and chkconfig.
Figure 4.1 shows the Service Configuration GUI with the NetworkManager service selected.
Figure 4.1 Service Configuration
53
Starting and Stopping Services
4.3.6 Starting and Stopping Services
To start a service, either run its /etc/init.d script directly with the start argument, for example:
# /etc/init.d/sshd start
Starting sshd:
[
OK
]
[
OK
]
[
OK
]
or use the service command with the start argument:
# service sshd start
Starting sshd:
Similarly, to stop a service, use the stop argument:
# service sshd stop
Stopping sshd:
Note
Changing the state of a service only lasts as long as the system remains at the
same run level. If you stop a service and then change the system's run state to one
in which the service is configured to run (for example, by rebooting the system), the
service restarts.
Some scripts take other arguments, such as restart, reload, and status. Omitting an argument
displays a usage message:
# service sshd
Usage: /etc/init.d/sshd {start|stop|restart|reload|force-reload|condrestart|try-restart|status}
If supported, you can use the status argument to view the status of a service:
# service sshd status
openssh-daemon (pid 12101) is running...
For more information, see the service(8) manual page.
4.3.7 Configuring Services to Start at Different Run Levels
You can use the chkconfig command to define in which run levels a service should run, to list startup
information for services, and to check the state of services. chkconfig changes the configuration of the
symbolic links in the /etc/rcN.d directories.
Note
You cannot use chkconfig to change the current state of a service. To stop or
start a service, use the service command.
To list the run-level configuration of all services that run their own daemon:
# chkconfig --list
NetworkManager 0:off
abrt-ccpp
0:off
abrt-oops
0:off
abrtd
0:off
acpid
0:off
atd
0:off
...
1:off
1:off
1:off
1:off
1:off
1:off
2:on
2:off
2:off
2:off
2:on
2:off
3:on
3:on
3:on
3:on
3:on
3:on
4:on
4:off
4:off
4:off
4:on
4:on
5:on
5:on
5:on
5:on
5:on
5:on
6:off
6:off
6:off
6:off
6:off
6:off
The command lists each service, followed by its configured state for each run level. For example, the abrtd
service is configured to run at run levels 3 and 5.
54
Configuring Services to Start at Different Run Levels
To view the configuration of a particular service, such as ntpd, specify its name as an argument:
# chkconfig --list ntpd
ntpd
0:off 1:off 2:on 3:on 4:on 5:on 6:off
To enable a service to run at run levels 2,3, 4, or 5, use the on argument:
# chkconfig httpd on
# chkconfig --list httpd
httpd
0:off 1:off 2:on 3:on 4:on 5:on 6:off
To enable the service for certain run levels only, specify the --level option followed by a concatenated
list of the run levels, for example:
# chkconfig --level 35 httpd on
# chkconfig --list httpd
httpd
0:off 1:off 2:off 3:on 4:off 5:on 6:off
Similarly, the off argument disables a service for run levels 2, 3, 4, and 5, or for the run levels specified by
--level, for example:
# chkconfig
# chkconfig
sshd
# chkconfig
# chkconfig
sshd
# chkconfig
# chkconfig
sshd
sshd off
--list sshd
0:off 1:off
sshd on
--list sshd
0:off 1:off
--level 34 sshd
--list sshd
0:off 1:off
2:off 3:off 4:off 5:off 6:off
2:on 3:on 4:on 5:on 6:off
off
2:on 3:off 4:off 5:on 6:off
The chkconfig command changes the configuration of a service to run at a particular run level. It does
not change the current state of a service as this example shows:
# runlevel
N 5
# chkconfig sshd off
# chkconfig --list sshd
sshd
0:off 1:off 2:off 3:off 4:off 5:off 6:off
# service sshd status
openssh-daemon (pid 12101) is running...
The changed configuration of the sshd service takes effect only when you next change the system's
run state, for example, by rebooting the system. You could, of course, use the service sshd stop
command to stop the service.
For more information, see the chkconfig(8) manual page.
55
56
Chapter 5 System Configuration Settings
Table of Contents
5.1 About /etc/sysconfig Files ............................................................................................................ 57
5.2 About the /proc Virtual File System .............................................................................................. 58
5.2.1 Virtual Files and Directories Under /proc ........................................................................... 59
5.2.2 Changing Kernel Parameters ............................................................................................ 62
5.2.3 Parameters that Control System Performance ................................................................... 63
5.2.4 Parameters that Control Kernel Panics ............................................................................. 64
5.3 About the /sys Virtual File System ............................................................................................... 65
5.3.1 Virtual Directories Under /sys ............................................................................................ 65
This chapter describes the files and virtual file systems that you can use to change configuration settings
for your system.
5.1 About /etc/sysconfig Files
The /etc/sysconfig directory contains files that control your system's configuration. The contents of
this directory depend on the packages that you have installed on your system.
Some of the files that you might find in the /etc/sysconfig directory include:
atd
Specifies additional command line arguments for the atd daemon.
authconfig
Specifies whether various authentication mechanisms and options may be
used. For example, the entry USEMKHOMEDIR=no disables the creation of a
home directory for a user when he or she first logs in.
autofs
Defines custom options for automatically mounting devices and controlling the
operation of the automounter.
crond
Passes arguments to the crond daemon at boot time.
i18n
Defines the default language, any other supported languages, and the default
system font.
init
Controls how the system appears and functions during the boot process.
ip6tables-config
Stores information that the kernel uses to set up IPv6 packet filtering services
when the iptables service starts.
ip6tables
Stores firewall configuration rules for IPv6.
iptables-config
Stores information that the kernel uses to set up IPv4 packet filtering services
when the iptables service starts.
iptables
Stores firewall configuration rules for IPv4.
keyboard
Specifies the keyboard.
modules (directory)
Contains scripts that the kernel runs to load additional modules at boot time.
A script in the modules directory must have the extension .modules and
it must have 755 executable permissions. For an example, see the bluezuinput.modules script that loads the uinput module. For more information,
see Section 6.5, “Specifying Modules to be Loaded at Boot Time”.
57
About the /proc Virtual File System
named
Passes arguments to the name service daemon at boot time. The named
daemon is a Domain Name System (DNS) server that is part of the Berkeley
Internet Name Domain (BIND) distribution. This server maintains a table that
associates host names with IP addresses on the network.
network
Specifies the host name of the system and whether networking is configured.
nfs
Controls which ports remote procedure call (RPC) services use for NFS v2
and v3. This file allows you to set up firewall rules for NFS v2 and v3. Firewall
configuration for NFS v4 does not require you to edit this file.
ntpd
Passes arguments to the network time protocol (NTP) daemon at boot time.
samba
Passes arguments to the smbd, nmbd, and winbindd daemons at boot time
to support file-sharing connectivity for Windows clients, NetBIOS-over-IP
naming service, and connection management to domain controllers.
For more information, see /usr/share/doc/initscripts*/sysconfig.txt.
5.2 About the /proc Virtual File System
The files in the /proc directory hierarchy contain information about your system hardware and the
processes that are running on the system. You can change the configuration of the kernel by writing to
certain files that have write permission.
The name of the proc file system stems from its original purpose on the Oracle Solaris operating system,
which was to allow access by debugging tools to the data structures inside running processes. Linux added
this interface and extended it to allow access to data structures in the kernel. Over time, /proc became
quite disordered and the sysfs file system was created in an attempt to tidy it up. For more information,
see Section 5.3, “About the /sys Virtual File System”.
Files under the /proc directory are virtual files that the kernel creates on demand to present a browsable
view of the underlying data structures and system information. As such, /proc is an example of a virtual
file system. Most virtual files are listed as zero bytes in size, but they contain a large amount of information
when viewed.
Virtual files such as /proc/interrupts, /proc/meminfo, /proc/mounts, and /proc/partitions
provide a view of the system’s hardware. Others, such as /proc/filesystems and the files under /
proc/sys provide information about the system's configuration and allow this configuration to be modified.
Files that contain information about related topics are grouped into virtual directories. For example, a
separate directory exists in /proc for each process that is currently running on the system, and the
directory's name corresponds to the numeric process ID. /proc/1 corresponds to the init process,
which has a PID of 1.
You can use commands such as cat, less, and view to examine virtual files within /proc. For example,
/proc/cpuinfo contains information about the system's CPUs:
# cat /proc/cpuinfo
processor
:
vendor_id
:
cpu family
:
model
:
model name
:
stepping
:
cpu MHz
:
cache size
:
physical id
:
siblings
:
0
GenuineIntel
6
42
Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz
7
2393.714
6144 KB
0
2
58
Virtual Files and Directories Under /proc
core id
cpu cores
apicid
initial apicid
fpu
fpu_exception
cpuid level
wp
...
:
:
:
:
:
:
:
:
0
2
0
0
yes
yes
5
yes
Certain files under /proc require root privileges for access or contain information that is not humanreadable. You can use utilities such as lspci, free, and top to access the information in these files. For
example, lspci lists all PCI devices on a system:
# lspci
00:00.0
00:01.0
00:01.1
00:02.0
00:03.0
00:04.0
00:05.0
00:06.0
00:07.0
00:0b.0
00:0d.0
Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
IDE interface: Intel Corporation 82371AB/EB/MB PIIX4 IDE (rev 01)
VGA compatible controller: InnoTek Systemberatung GmbH VirtualBox Graphics Adapter
Ethernet controller: Intel Corporation 82540EM Gigabit Ethernet Controller (rev 02)
System peripheral: InnoTek Systemberatung GmbH VirtualBox Guest Service
Multimedia audio controller: Intel Corporation 82801AA AC'97 Audio Controller (rev 01)
USB controller: Apple Inc. KeyLargo/Intrepid USB
Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 08)
USB controller: Intel Corporation 82801FB/FBM/FR/FW/FRW (ICH6 Family) USB2 EHCI Controller
SATA controller: Intel Corporation 82801HM/HEM (ICH8M/ICH8M-E) SATA Controller [AHCI mode]
(rev 02)
...
5.2.1 Virtual Files and Directories Under /proc
The following table lists the most useful virtual files and directories under the /proc directory hierarchy.
Table 5.1 Useful Virtual Files and Directories Under /proc
Virtual File or Directory
Description
PID (Directory)
Provides information about the process with the process ID (PID).
The directory's owner and group is same as the process's. Useful files
under the directory include:
cmdline
Command path.
cwd
Symbolic link to the process's current working directory.
environ
Environment variables.
exe
Symbolic link to the command executable.
fd/N
File descriptors.
maps
Memory maps to executable and library files.
root
Symbolic link to the effective root directory for the process.
stack
The contents of the kernel stack.
status
Run state and memory usage.
buddyinfo
Provides information for diagnosing memory fragmentation.
bus (directory)
Contains information about the various buses (such as pci and
usb) that are available on the system. You can use commands such
59
Virtual Files and Directories Under /proc
Virtual File or Directory
Description
as lspci, lspcmcia, and lsusb to display information for such
devices.
cmdline
Lists parameters passed to the kernel at boot time.
cpuinfo
Provides information about the system's CPUs.
crypto
Provides information about all installed cryptographic cyphers.
devices
Lists the names and major device numbers of all currently configured
characters and block devices.
dma
Lists the direct memory access (DMA) channels that are currently in
use.
driver (directory)
Contains information about drivers used by the kernel, such as those
for non-volatile RAM (nvram), the real-time clock (rtc), and memory
allocation for sound (snd-page-alloc).
execdomains
Lists the execution domains for binaries that the Oracle Linux kernel
supports.
filesystems
Lists the file system types that the kernel supports. Entries marked
with nodev are not in use.
fs (directory)
Contains information about the file systems that are mounted,
organized by file system type.
interrupts
Records the number of interrupts per interrupt request queue (IRQ) for
each CPU since system startup.
iomem
Lists the system memory map for each physical device.
ioports
Lists the range of I/O port addresses that the kernel uses with devices.
irq (directory)
Contains information about each IRQ. You can configure the affinity
between each IRQ and the system CPUs.
kcore
Presents the system's physical memory in core file format that you
can examine using a debugger such as crash or gdb. This file is not
human-readable.
kmsg
Records kernel-generated messages, which are picked up by
programs such as dmesg.
loadavg
Displays the system load averages (number of queued processes) for
the past 1, 5, and 15 minutes, the number of running processes, the
total number of processes, and the PID of the process that is running.
locks
Displays information about the file locks that the kernel is currently
holding on behalf of processes. The information provided includes:
• lock class (FLOCK or POSIX)
• lock type (ADVISORY or MANDATORY)
• access type (READ or WRITE)
• process ID
• major device, minor device, and inode numbers
• bounds of the locked region
60
Virtual Files and Directories Under /proc
Virtual File or Directory
Description
mdstat
Lists information about multiple-disk RAID devices.
meminfo
Reports the system's usage of memory in more detail than is available
using the free or top commands.
modules
Displays information about the modules that are currently loaded
into the kernel. The lsmod command formats and displays the same
information, excluding the kernel memory offset of a module.
mounts
Lists information about all mounted file systems.
net (directory)
Provides information about networking protocol, parameters, and
statistics. Each directory and virtual file describes aspects of the
configuration of the system's network.
partitions
Lists the major and minor device numbers, number of blocks, and
name of partitions mounted by the system.
scsi/device_info
Provides information about supported SCSI devices.
scsi/scsi and
Provide information about configured SCSI devices, including vendor,
model, channel, ID, and LUN data .
scsi/sg/*
self
Symbolic link to the process that is examining /proc.
slabinfo
Provides detailed information about slab memory usage.
softirqs
Displays information about software interrupts (softirqs). A softirq
is similar to a hardware interrupt (hardirq) and allow the kernel to
perform asynchronous processing that would take too long during a
hardware interrupt.
stat
Records information about the system since it was started, including:
cpu
Total CPU time (measured in jiffies) spent in user mode, lowpriority user mode, system mode, idle, waiting for I/O, handling
hardirq events, and handling softirq events.
cpuN
Times for CPU N.
swaps
Provides information on swap devices. The units of size and usage
are kilobytes.
sys (directory)
Provides information about the system and also allows you to enable,
disable, or modify kernel features. You can write new settings to any
file that has write permission. See Section 5.2.2, “Changing Kernel
Parameters”.
The following subdirectory hierarchies of /proc/sys contain virtual
files, some of whose values you can usefully alter:
dev
Device parameters.
fs
File system parameters.
kernel
Kernel configuration parameters.
net
Networking parameters.
61
Changing Kernel Parameters
Virtual File or Directory
Description
sysvipc (directory)
Provides information about the usage of System V Interprocess
Communication (IPC) resources for messages (msg), semaphores
(sem), and shared memory (shm).
tty (directory)
Provides information about the available and currently used terminal
devices on the system. The drivers virtual file lists the devices that
are currently configured.
vmstat
Provides information about virtual memory usage.
For more information, see the proc(5) manual page.
5.2.2 Changing Kernel Parameters
Some virtual files under /proc, and under /proc/sys in particular, are writable and you can use them to
adjust settings in the kernel. For example, to change the host name, you can write a new value to /proc/
sys/kernel/hostname:
# echo www.mydomain.com > /proc/sys/kernel/hostname
Other files take value that take binary or Boolean values. For example, the value of /proc/sys/net/
ipv4/ip_forward determines whether the kernel forwards IPv4 network packets.
# cat /proc/sys/net/ipv4/ip_forward
0
# echo 1 > /proc/sys/net/ipv4/ip_forward
# cat /proc/sys/net/ipv4/ip_forward
1
You can use the sysctl command to view or modify values under the /proc/sys directory.
Note
Even root cannot bypass the file access permissions of virtual file entries under
/proc. If you attempt to change the value of a read-only entry such as /proc/
partitions, there is no kernel code to service the write() system call.
To display all of the current kernel settings:
# sysctl -a
kernel.sched_child_runs_first = 0
kernel.sched_min_granularity_ns = 2000000
kernel.sched_latency_ns = 10000000
kernel.sched_wakeup_granularity_ns = 2000000
kernel.sched_shares_ratelimit = 500000
...
Note
The delimiter character in the name of a setting is a period (.) rather than a slash
(/) in a path relative to /proc/sys. For example, net.ipv4.ip_forward
represents net/ipv4/ip_forward and kernel.msgmax represents kernel/
msgmax.
To display an individual setting, specify its name as the argument to sysctl:
# sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 0
62
Parameters that Control System Performance
To change the value of a setting, use the following form of the command:
# sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1
Changes that you make in this way remain in force only until the system is rebooted. To make
configuration changes persist after the system is rebooted, you must add them to the /etc/sysctl.conf
file. Any changes that you make to this file take effect when the system reboots or if you run the sysctl p command, for example:
# sed -i '/net.ipv4.ip_forward/s/= 0/= 1/' /etc/sysctl.conf
# grep ip_forward /etc/sysctl.conf
net.ipv4.ip_forward = 1
# sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 0
# sysctl -p
net.ipv4.ip_forward = 1
net.ipv4.conf.default.rp_filter = 1
...
kernel.shmall = 4294967296
# sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1
For more information, see the sysctl(8) and sysctl.conf(5) manual pages.
5.2.3 Parameters that Control System Performance
The following parameters control aspects of system performance:
fs.file-max
Specifies the maximum number of open files for all processes. Increase the value of this parameter if you
see messages about running out of file handles.
net.core.netdev_max_backlog
Specifies the size of the receiver backlog queue, which is used if an interface receives packets faster than
the kernel can process them. If this queue is too small, packets are lost at the receiver, rather than on the
network.
net.core.rmem_max
Specifies the maximum read socket buffer size. To minimize network packet loss, this buffer must be large
enough to handle incoming network packets.
net.core.wmem_max
Specifies the maximum write socket buffer size. To minimize network packet loss, this buffer must be large
enough to handle outgoing network packets.
net.ipv4.tcp_available_congestion_control
Displays the TCP congestion avoidance algorithms that are available for use. Use the modprobe
command if you need to load additional modules such as tcp_htcp to implement the htcp algorithm.
net.ipv4.tcp_congestion_control
Specifies which TCP congestion avoidance algorithm is used.
63
Parameters that Control Kernel Panics
net.ipv4.tcp_max_syn_backlog
Specifies the number of outstanding SYN requests that are allowed. Increase the value of this parameter
if you see synflood warnings in your logs, and investigation shows that they are occurring because the
server is overloaded by legitimate connection attempts.
net.ipv4.tcp_rmem
Specifies minimum, default, and maximum receive buffer sizes that are used for a TCP socket. The
maximum value cannot be larger than net.core.rmem_max.
net.ipv4.tcp_wmem
Specifies minimum, default, and maximum send buffer sizes that are used for a TCP socket. The maximum
value cannot be larger than net.core.wmem_max.
vm.swappiness
Specifies how likely the kernel is to write loaded pages to swap rather than drop pages from the system
page cache. When set to 0, swapping only occurs to avoid an out of memory condition. When set to
100, the kernel swaps aggressively. For a desktop system, setting a lower value can improve system
responsiveness by decreasing latency. The default value is 60.
Caution
This parameter is intended for use with laptops to reduce power consumption by the
hard disk. Do not adjust this value on server systems.
5.2.4 Parameters that Control Kernel Panics
The following parameters control the circumstances under which a kernel panic can occur:
kernel.hung_task_panic
If set to 1, the kernel panics if any user or kernel thread sleeps in the TASK_UNINTERRUPTIBLE state (D
state) for more than kernel.hung_task_timeout_secs seconds. A process remains in D state while
waiting for I/O to complete. You cannot kill or interrupt a process in this state.
The default value is 0, which disables the panic.
Tip
To diagnose a hung thread, you can examine /proc/PID/stack, which displays
the kernel stack for both kernel and user threads.
kernel.hung_task_timeout_secs
Specifies how long a user or kernel thread can remain in D state before a message is generated or the
kernel panics (if the value of kernel.hung_task_panic is 1). The default value is 120 seconds.
kernel.panic
Specifies the number of seconds after a panic before a system will automatically reset itself.
If the value is 0, the system hangs, which allows you to collect detailed information about the panic for
troubleshooting. This is the default value.
64
About the /sys Virtual File System
To enable automatic reset, set a non-zero value. If you require a memory image (vmcore), allow enough
time for Kdump to create this image. The suggested value is 30 seconds, although large systems will
require a longer time.
kernel.panic_on_oops
If set to 0, the system tries to continue operations if the kernel encounters an oops or BUG condition. When
set to 1 (default), the system delays a few seconds to give the kernel log daemon, klogd, time to record
the oops output before the panic occurs.
In an OCFS2 cluster. set the value to 1 to specify that a system must panic if a kernel oops occurs. If
a kernel thread required for cluster operation crashes, the system must reset itself. Otherwise, another
node might not be able to tell whether a node is slow to respond or unable to respond, causing cluster
operations to hang.
vm.panic_on_oom
If set to 0 (default), the kernel’s OOM-killer scans through the entire task list and attempts to kill a
memory-hogging process to avoid a panic. When set to 1, the kernel panics but can survive under certain
conditions. If a process limits allocations to certain nodes by using memory policies or cpusets, and those
nodes reach memory exhaustion status, the OOM-killer can kill one process. No panic occurs in this case
because other nodes’ memory might be free and the system as a whole might not yet be out of memory.
When set to 2, the kernel always panics when an OOM condition occurs. Settings of 1 and 2 are for
intended for use with clusters, depending on your preferred failover policy.
5.3 About the /sys Virtual File System
In addition to /proc, the kernel exports information to the /sys virtual file system (sysfs). Programs such
as the dynamic device manager, udev, use /sys to access device and device driver information. The
implementation of /sys has helped to tidy up the /proc file system as most hardware information has
been moved to /sys.
Note
/sys exposes kernel data structures and control points, which implies that it might
contain circular references, where a directory links to an ancestor directory. As a
result, a find command used on /sys might never terminate.
5.3.1 Virtual Directories Under /sys
The following table lists the most useful virtual directories under the /sys directory hierarchy.
Table 5.2 Useful Virtual Directories Under /sys
Virtual Directory
Description
block
Contains subdirectories for block devices. For example: /sys/
block/sda.
bus
Contains subdirectories for each supported physical bus type, such
as pci, pcmcia, scsi, or usb. Under each bus type, the devices
directory lists discovered devices, and the drivers directory contains
directories for each device driver.
class
Contains subdirectories for every class of device that is registered with
the kernel.
65
Virtual Directories Under /sys
Virtual Directory
Description
devices
Contains the global device hierarchy of all devices on the system.
The platform directory contains peripheral devices such as device
controllers that are specific to a particular platform. The system
directory contains non-peripheral devices such as CPUs and APICs.
The virtual directory contains virtual and pseudo devices. See
Chapter 7, Device Management.
firmware
Contains subdirectories for firmware objects.
module
Contains subdirectories for each module loaded into the kernel.
You can alter some parameter values for loaded modules. See
Section 6.4, “About Module Parameters”.
power
Contains attributes that control the system's power state.
For more information, see https://www.kernel.org/doc/Documentation/filesystems/sysfs.txt.
66
Chapter 6 Kernel Modules
Table of Contents
6.1
6.2
6.3
6.4
6.5
About Kernel Modules .................................................................................................................
Listing Information about Loaded Modules ...................................................................................
Loading and Unloading Modules .................................................................................................
About Module Parameters ...........................................................................................................
Specifying Modules to be Loaded at Boot Time ...........................................................................
67
67
68
69
70
This chapter describes how to load, unload, and modify the behavior of kernel modules.
6.1 About Kernel Modules
The boot loader loads the kernel into memory. You can add new code to the kernel by including the source
files in the kernel source tree and recompiling the kernel. Kernel modules, which can be dynamically
loaded and unloaded on demand, provide device drivers that allow the kernel to access new hardware,
support different file system types, and extend its functionality in other ways. To avoid wasting memory on
unused device drivers, Oracle Linux supports loadable kernel modules (LKMs), which allow a system to
run with only the device drivers and kernel code that it requires loaded into memory.
6.2 Listing Information about Loaded Modules
Use the lsmod command to list the modules that are currently loaded into the kernel.
# lsmod
Module
nls_utf8
fuse
tun
autofs4
...
ppdev
parport_pc
parport
...
Size
1405
59164
12079
22739
Used by
1
0
0
3
7901
21262
33812
0
0
2 ppdev,parport_pc
Note
This command produces its output by reading the /proc/modules file.
The output shows the module name, the amount of memory it uses, the number of processes using the
module and the names of other modules on which it depends. In the sample output, the module parport
depends on the modules ppdev and parport_pc, which are loaded in advance of parport. Two
processes are currently using all three modules.
To display detailed information about a module, use the modinfo command, for example:
# modinfo ahci
filename:
version:
license:
description:
author:
srcversion:
/lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/drivers/ata/ahci.ko
3.0
GPL
AHCI SATA low-level driver
Jeff Garzik
AC5EC885397BF332DE16389
67
Loading and Unloading Modules
alias:
...
depends:
vermagic:
parm:
parm:
...
pci:v*d*sv*sd*bc01sc06i01*
2.6.32-300.27.1.el6uek.x86_64 SMP mod_unload modversions
skip_host_reset:skip global host reset (0=don't skip, 1=skip) (int)
ignore_sss:Ignore staggered spinup flag (0=don't ignore, 1=ignore) (int)
The output includes the following information:
filename
Absolute path of the kernel object file.
version
Version number of the module.
description
Short description of the module.
srcversion
Hash of the source code used to create the module.
alias
Internal alias names for the module.
depends
Comma-separated list of any modules on which this module depends.
vermagic
Kernel version that was used to compile the module, which is checked against the current
kernel when the module is loaded.
parm
Module parameters and descriptions.
Modules are loaded into the kernel from kernel object (ko) files in the /lib/
modules/kernel_version/kernel directory. To display the absolute path of a kernel object file,
specify the -n option, for example:
# modinfo -n parport
/lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/drivers/parport/parport.ko
For more information, see the lsmod(5) and modinfo(8) manual pages.
6.3 Loading and Unloading Modules
The modprobe command loads kernel modules, for example:
# modprobe nfs
# lsmod | grep nfs
nfs
lockd
fscache
nfs_acl
auth_rpcgss
sunrpc
266415
66530
41704
2477
38976
204268
0
1
1
1
1
5
nfs
nfs
nfs
nfs
nfs,lockd,nfs_acl,auth_rpcgss
Use the -v verbose option to show if any additional modules are loaded to resolve dependencies.
# modprobe -v nfs
insmod /lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/net/sunrpc/auth_gss/auth_rpcgss.ko
insmod /lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/fs/nfs_common/nfs_acl.ko
insmod /lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/fs/fscache/fscache.ko
...
To determine the dependencies, the modprobe command queries the /lib/
modules/kernel_version/modules.dep file, which the depmod utility creates when you install kernel
modules.
68
About Module Parameters
Note
modprobe does not reload modules that are already loaded. You must first unload
a module before you can load it again.
Use the -r option to unload kernel modules, for example:
# modprobe -rv nfs
rmmod /lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/fs/nfs/nfs.ko
rmmod /lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/fs/lockd/lockd.ko
rmmod /lib/modules/2.6.32-300.27.1.el6uek.x86_64/kernel/fs/fscache/fscache.ko
...
Modules are unloaded in the reverse order that they were loaded. Modules are not unloaded if a process or
another loaded module requires them.
Note
modprobe uses the insmod and rmmod utilities to load and unload modules. As
insmod and rmmod do not resolve module dependencies, do not use these utilities.
For more information, see the modprobe(8) and modules.dep(5) manual pages.
6.4 About Module Parameters
Modules accept parameters that you can specify using modprobe to modify a module's behavior:
# modprobe module_name parameter=value ...
Use spaces to separate multiple parameter/value pairs. Array values are represented by a commaseparated list, for example:
# modprobe foo arrayparm=1,2,3,4
You can also change the values of some parameters for loaded modules and built-in drivers by writing the
new value to a file under /sys/module/module_name/parameters, for example:
# echo 0 > /sys/module/ahci/parameters/skip_host_reset
The /etc/modprobe.d directory contains .conf configuration files specify module options, create
module aliases, and override the usual behavior of modprobe for modules with special requirements.
The /etc/modprobe.conf file that was used with earlier versions of modprobe is also valid if it exists.
Entries in the /etc/modprobe.conf and /etc/modprobe.d/*.conf files use the same syntax.
The following are commonly used commands in modprobe configuration files:
alias
Creates an alternate name for a module. The alias can include shell wildcards. For example,
create an alias for the sd-mod module:
alias block-major-8-* sd_mod
As a result, a command such as modprobe block-major-8-0 has the same effect as
modprobe sd_mod.
blacklist
Ignore a module's internal alias that is displayed by the modinfo command. This command
is typically used if the associated hardware is not required, if two or more modules both
support the same devices, or if a module invalidly claims to support a device. For example,
blacklist the alias for the frame-buffer driver cirrusfb:
69
Specifying Modules to be Loaded at Boot Time
blacklist cirrusfb
The /etc/modprobe.d/blacklist.conf file prevents hotplug scripts from loading a
module, usually so that a different driver binds the module instead, regardless of which
driver happens to be probed first.
install
Runs a shell command instead of loading a module into the kernel. For example, load the
module snd-emu10k1-synth instead of snd-emu10k1:
install snd-emu10k1 /sbin/modprobe --ignore-install snd-emu10k1 && \
/sbin/modprobe snd-emu10k1-synth
options
Defines options for a module,. For example, define the nohwcrypt and qos options for the
b43 module:
options b43 nohwcrypt=1 qos=0
remove
Runs a shell command instead of unloading a module. For example, unmount /proc/fs/
nfsd before unloading the nfsd module:
remove nfsd { /bin/umount /proc/fs/nfsd > /dev/null 2>&1 || :; } ; \
/sbin/modprobe -r --first-time --ignore-remove nfsd
For more information, see the modprobe.conf(5) manual page.
6.5 Specifying Modules to be Loaded at Boot Time
The following lines in /etc/rc.sysinit defines how the init process runs scripts in the /etc/
sysconfig/modules directory at boot time:
# Load other user-defined modules
for file in /etc/sysconfig/modules/*.modules ; do
[ -x $file ] && $file
done
To load a module at boot time:
1. Create a file in the /etc/sysconfig/modules directory. The file name must have the extension
.modules, for example foo.modules.
2. Edit the file to create the script that loads the module.
The script to load a module can be a simple modprobe call, for example:
#!/bin/sh
modprobe foo
or more complex to include error handling:
#!/bin/sh
if [ ! -c /dev/foo ] ; then
exec /sbin/modprobe foo > /dev/null 2>&1
fi
3. Use the following command to make the script executable:
# chmod 755 /etc/sysconfig/modules/foo.modules
70
Chapter 7 Device Management
Table of Contents
7.1
7.2
7.3
7.4
7.5
About Device Files ......................................................................................................................
About the Udev Device Manager .................................................................................................
About Udev Rules ......................................................................................................................
Querying Udev and Sysfs ...........................................................................................................
Modifying Udev Rules .................................................................................................................
71
73
73
76
79
This chapter describes how the system uses device files and how the udev device manager dynamically
creates or removes device node files.
7.1 About Device Files
The /dev directory contains device files (also sometimes known as device special files and device nodes)
that provide access to peripheral devices such as hard disks, to resources on peripheral devices such as
disk partitions, and pseudo devices such as a random number generator.
The /dev directory has several subdirectory hierarchies, each of which holds device files that relate to
a certain type of device. For example, the /dev/disk/id-by-uuid directory contains device files for
hard disks named according to the universally unique identifier (UUID) for the disk. The device files in
subdirectories such as these are actually implemented as symbolic links to device files in /dev. You can
access the same device using the file in /dev or the corresponding link to the file listed in /dev/disk/
id-by-uuid.
If you use the ls -l command to list the files under /dev, you see that some device files are shown as
being either type b for block or type c for character. These devices have a pair of numbers associated with
them instead of a file size. These major and minor numbers identify the device to the system.
# ls -l /dev
total 0
crw-rw----. 1
drwxr-xr-x. 2
drwxr-xr-x. 2
drwxr-xr-x. 3
lrwxrwxrwx. 1
drwxr-xr-x. 2
crw-------. 1
lrwxrwxrwx. 1
drwxr-xr-x. 4
crw-rw----. 1
drwxr-xr-x. 6
brw-rw----. 1
brw-rw----. 1
...
crw-rw-rw-. 1
...
drwxr-xr-x. 2
...
crw-rw-rw-. 1
...
brw-rw----. 1
brw-rw----. 1
brw-rw----. 1
...
lrwxrwxrwx. 1
lrwxrwxrwx. 1
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
root
disk
disk
root
root
10,
56
640
80
60
3
2880
5,
1
11
100
10, 61
120
253,
0
253,
1
1,
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
17
17
17
17
17
17
17
17
17
17
17
17
17
08:17
08:17
08:16
08:16
08:17
08:17
08:17
08:17
08:17
08:17
08:16
08:17
08:17
autofs
block
bsg
bus
cdrom -> sr0
char
console
core -> /proc/kcore
cpu
cpu_dma_latency
disk
dm-0
dm-1
3 Mar 17 08:17 /dev/null
root
root
0 Mar 17 08:16 pts
root
root
1,
8 Mar 17 08:17 random
root
root
root
disk
disk
disk
8,
8,
8,
0 Mar 17 08:17 sda
1 Mar 17 08:17 sda1
2 Mar 17 08:17 sda2
root
root
root
root
15 Mar 17 08:17 stderr -> /proc/self/fd/2
15 Mar 17 08:17 stdin -> /proc/self/fd/0
71
About Device Files
lrwxrwxrwx.
...
crw--w----.
crw--w----.
...
crw-rw-rw-.
...
crw-rw-rw-.
1 root
root
15 Mar 17 08:17 stdout -> /proc/self/fd/1
1 root
1 root
tty
tty
4,
4,
0 Mar 17 08:17 tty0
1 Mar 17 08:17 tty1
1 root
root
1,
9 Mar 17 08:17 urandom
1 root
root
1,
5 Mar 17 08:17 zero
Block devices support random access to data, seeking media for data, and usually allow data to be
buffered while it is being written or read. Examples of block devices include hard disks, CD-ROM drives,
flash memory, and other addressable memory devices. The kernel writes data to or reads data from a
block device in blocks of a certain number of bytes. In the sample output, sda is the block device file that
corresponds to the hard disk, and it has a major number of 8 and a minor number of 0. sda1 and sda2 are
partitions of this disk, and they have the same major number as sda (8), but their minor numbers are 1 and
2.
Character devices support streaming of data to or from a device, and data is not usually buffered nor is
random access permitted to data on a device. The kernel writes data to or reads data from a character
device one byte at a time. Examples of character devices include keyboards, mice, terminals, pseudoterminals, and tape drives. tty0 and tty1 are character device files that correspond to terminal devices
that allow users to log in from serial terminals or terminal emulators. These files have major number 4 and
minor numbers 0 and 1.
Pseudo-terminals slave devices emulate real terminal devices to interact with software. For example, a
user might log in on a terminal device such as /dev/tty1, which then uses the pseudo-terminal master
device /dev/pts/ptmx to interact with an underlying pseudo-terminal device. The character device files
for pseudo-terminal slaves and master are located in the /dev/pts directory:
# ls -l /dev/pts
total 0
crw--w----. 1 guest
crw--w----. 1 guest
crw--w----. 1 guest
c---------. 1 root
tty 136, 0 Mar 17
tty 136, 1 Mar 17
tty 136, 2 Mar 17
root
5, 2 Mar 17
10:11
10:53
10:11
08:16
0
1
2
ptmx
Some device entries, such as stdin for the standard input, are symbolically linked via the self
subdirectory of the proc file system. The pseudo-terminal device file to which they actually point depends
on the context of the process.
# ls -l /proc/self/fd/[012]
total 0
lrwx------. 1 root root 64 Mar 17 10:02 0 -> /dev/pts/1
lrwx------. 1 root root 64 Mar 17 10:02 1 -> /dev/pts/1
lrwx------. 1 root root 64 Mar 17 10:02 2 -> /dev/pts/1
Character devices such as null, random, urandom, and zero are examples of pseudo-devices that
provide access to virtual functionality implemented in software rather than to physical hardware.
/dev/null is a data sink. Data that you write to /dev/null effectively disappears but the write operation
succeeds. Reading from /dev/null returns EOF (end-of-file).
/dev/zero is a data source of an unlimited number of zero-value bytes.
/dev/random and /dev/urandom are data sources of streams of pseudo-random bytes. To maintain
high-entropy output, /dev/random blocks if its entropy pool does not contains sufficient bits of noise. /
dev/urandom does not block and, as a result, the entropy of its output might not be as consistently high
as that of /dev/random. However, neither /dev/random nor /dev/urandom are considered to be truly
random enough for the purposes of secure cryptography such as military-grade encryption.
72
About the Udev Device Manager
You can find out the size of the entropy pool and the entropy value for /dev/random from virtual files
under /proc/sys/kernel/random:
# cat /proc/sys/kernel/random/poolsize
4096
# cat /proc/sys/kernel/random/entropy_avail
3467
For more information, see the null(4), pts(4), and random(4) manual pages.
7.2 About the Udev Device Manager
The udev device manager dynamically creates or removes device node files at boot time or if you add a
device to or remove a device from the system with a 2.6 version kernel or later. When creating a device
node, udev reads the device’s /sys directory for attributes such as the label, serial number, and bus
device number.
Udev can use persistent device names to guarantee consistent naming of devices across reboots,
regardless of their order of discovery. Persistent device names are especially important when using
external storage devices.
The configuration file for udev is /etc/udev/udev.conf, in which you can define the following variables:
udev_log
The logging priority, which can be set to err, info and debug. The default value is err.
udev_root
Specifies the location of the device nodes. The default value is /dev.
For more information, see the udev(7) manual page.
7.3 About Udev Rules
Udev uses rules files that determine how it identifies devices and creates device names. The udev daemon
(udevd) reads the rules files at system startup and stores the rules in memory. If the kernel discovers a
new device or an existing device goes offline, the kernel sends an event action (uevent) notification to
udevd, which matches the in-memory rules against the device attributes in /sys to identify the device. As
part of device event handling, rules can specify additional programs that should run to configure a device.
Rules files, which have the file extension .rules, are located in the following directories:
/lib/udev/rules.d
Contains default rules files. Do not edit these files.
/etc/udev/rules.d/
*.rules
Contains customized rules files. You can modify these files.
/dev/.udev/rules.d/
*.rules
Contains temporary rules files. Do not edit these files.
udevd processes the rules files in lexical order, regardless of which directory they are located. Rules files
in /etc/udev/rules.d override files of the same name in /lib/udev/rules.d.
The following rules are extracted from the file /lib/udev/rules.d/50-udev- default.rules and
illustrate the syntax of udev rules.
# do not edit this file, it will be overwritten on update
SUBSYSTEM=="block", SYMLINK{unique}+="block/%M:%m"
SUBSYSTEM!="block", SYMLINK{unique}+="char/%M:%m"
KERNEL=="pty[pqrstuvwxyzabcdef][0123456789abcdef]", GROUP="tty", MODE="0660"
73
About Udev Rules
KERNEL=="tty[pqrstuvwxyzabcdef][0123456789abcdef]", GROUP="tty", MODE="0660"
...
# mem
KERNEL=="null|zero|full|random|urandom", MODE="0666"
KERNEL=="mem|kmem|port|nvram", GROUP="kmem", MODE="0640"
...
# block
SUBSYSTEM=="block", GROUP="disk"
...
# network
KERNEL=="tun",
MODE="0666"
KERNEL=="rfkill",
MODE="0644"
# CPU
KERNEL=="cpu[0-9]*",
MODE="0444"
...
# do not delete static device nodes
ACTION=="remove", NAME=="", TEST=="/lib/udev/devices/%k", \
OPTIONS+="ignore_remove"
ACTION=="remove", NAME=="?*", TEST=="/lib/udev/devices/$name", \
OPTIONS+="ignore_remove"
Comment lines begin with a # character. All other non-blank lines define a rule, which is a list of one or
more comma-separated key-value pairs. A rule either assigns a value to a key or it tries to find a match for
a key by comparing its current value with the specified value. The following table shows the assignment
and comparison operators that you can use.
Operator
Description
=
Assign a value to a key, overwriting any previous value.
+=
Assign a value by appending it to the key's current list of values.
:=
Assign a value to a key. This value cannot be changed by any further rules.
==
Match the key's current value against the specified value for equality.
!=
Match the key's current value against the specified value for equality.
You can use the following shell-style pattern matching characters in values.
Character
Description
?
Matches a single character.
*
Matches any number of characters, including zero.
[]
Matches any single character or character from a range of characters specified
within the brackets. For example, tty[sS][0-9] would match ttys7 or ttyS7.
The following table lists commonly used match keys in rules.
Match Key
Description
ACTION
Matches the name of the action that led to an event. For example, ACTION="add"
or ACTION="remove".
ENV{key}
Matches a value for the device property key. For example,
ENV{DEVTYPE}=="disk".
KERNEL
Matches the name of the device that is affected by an event. For example,
KERNEL=="dm-*" for disk media.
NAME
Matches the name of a device file or network interface. For example, NAME="?*" for
any name that consists of one or more characters.
74
About Udev Rules
Match Key
Description
SUBSYSTEM
Matches the subsystem of the device that is affected by an event. For example,
SUBSYSTEM=="tty".
TEST
Tests if the specified file or path exists. For example, TEST=="/lib/udev/
devices/$name", where $name is the name of the currently matched device file.
Other match keys include ATTR{filename}, ATTRS{filename}, DEVPATH, DRIVER, DRIVERS,
KERNELS, PROGRAM, RESULT, SUBSYSTEMS, and SYMLINK.
The following table lists commonly used assignment keys in rules.
Assignment Key
Description
ENV{key}
Specifies a value for the device property key. For example, GROUP="disk".
GROUP
Specifies the group for a device file. For example, GROUP="disk".
IMPORT{type}
Specifies a set of variables for the device property, depending on type:
cmdline
Import a single property from the boot kernel command line. For
simple flags, udevd sets the value of the property to 1. For example,
IMPORT{cmdline}="nodmraid".
db
Interpret the specified value as an index into the device database and
import a single property, which must have already been set by an earlier
event. For example, IMPORT{db}="DM_UDEV_LOW_PRIORITY_FLAG".
file
Interpret the specified value as the name of a text file and import its
contents, which must be in environmental key format. For example,
IMPORT{file}="keyfile".
parent
Interpret the specified value as a key-name filter and import the stored
keys from the database entry for the parent device. For example
IMPORT{parent}="ID_*".
program
Run the specified value as an external program and imports its
result, which must be in environmental key format. For example
IMPORT{program}="usb_id --export %p".
MODE
Specifies the permissions for a device file. For example, MODE="0640".
NAME
Specifies the name of a device file. For example, NAME="eth0".
OPTIONS
Specifies rule and device options. For example, OPTIONS+="ignore_remove",
which means that the device file is not removed if the device is removed.
OWNER
Specifies the owner for a device file. For example, GROUP="root".
RUN
Specifies a command to be run after the device file has been created. For example,
RUN+="/usr/bin/eject $kernel", where $kernel is the kernel name of the
device.
SYMLINK
Specifies the name of a symbolic link to a device file. For example, SYMLINK
+="disk/by-uuid/$env{ID_FS_UUID_ENC}", where $env{} is substituted
with the specified device property.
Other assignment keys include ATTR{key}, GOTO, LABEL, RUN, and WAIT_FOR.
The following table shows string substitutions that are commonly used with the GROUP, MODE, NAME,
OWNER, PROGRAM, RUN, and SYMLINK keys.
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Querying Udev and Sysfs
String Substitution Description
$attr{file} or
Specifies the value of a device attribute from a file under /sys. For example,
ENV{MATCHADDR}="$attr{address}".
%s{file}
$devpath or
The device path of the device in the sysfs file system under /sys. For example,
RUN+="keyboard-force-release.sh $devpath common-volume-keys".
%p
$env{key} or
Specifies the value of a device property. For example, SYMLINK+="disk/by-id/
md-name-$env{MD_NAME}-part%n".
%E{key}
$kernel or
The kernel name for the device.
%k
$major or
Specifies the major number of a device. For example,
IMPORT{program}="udisks-dm-export %M %m".
%M
$minor or
%m
$name
Specifies the minor number of a device. For example, RUN
+="$env{LVM_SBIN_PATH}/lvm pvscan --cache --major $major -minor $minor".
Specifies the device file of the current device. For example, TEST=="/lib/udev/
devices/$name".
Udev expands the strings specified for RUN immediately before its program is executed, which is after udev
has finished processing all other rules for the device. For the other keys, udev expands the strings while it
is processing the rules.
For more information, see the udev(7) manual page.
7.4 Querying Udev and Sysfs
You can use the udevadm command to query the udev database and sysfs.
For example, to query the sysfs device path relative to /sys that corresponds to the device file /dev/
sda:
# udevadm info --query=path --name=/dev/sda
/devices/pci0000:00/0000:00:0d.0/host0/target0:0:0/0:0:0:0/block/sda
To query the symbolic links that point to /dev/sda:
# udevadm info --query=symlink --name=/dev/sda
block/8:0
disk/by-id/ata-VBOX_HARDDISK_VB6ad0115d-356e4c09
disk/by-id/scsi-SATA_VBOX_HARDDISK_VB6ad0115d-356e4c09
disk/by-path/pci-0000:00:0d.0-scsi-0:0:0:0
The paths are relative to udev_root (by default, /dev).
To query the properties of /dev/sda:
# udevadm info --query=property --name=/dev/sda
UDEV_LOG=3
DEVPATH=/devices/pci0000:00/0000:00:0d.0/host0/target0:0:0/0:0:0:0/block/sda
MAJOR=8
MINOR=0
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Querying Udev and Sysfs
DEVNAME=/dev/sda
DEVTYPE=disk
SUBSYSTEM=block
ID_ATA=1
ID_TYPE=disk
ID_BUS=ata
ID_MODEL=VBOX_HARDDISK
ID_MODEL_ENC=VBOX\x20HARDDISK\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20...
ID_REVISION=1.0
ID_SERIAL=VBOX_HARDDISK_VB579a85b0-bf6debae
ID_SERIAL_SHORT=VB579a85b0-bf6debae
ID_ATA_WRITE_CACHE=1
ID_ATA_WRITE_CACHE_ENABLED=1
ID_ATA_FEATURE_SET_PM=1
ID_ATA_FEATURE_SET_PM_ENABLED=1
ID_ATA_SATA=1
ID_ATA_SATA_SIGNAL_RATE_GEN2=1
ID_SCSI_COMPAT=SATA_VBOX_HARDDISK_VB579a85b0-bf6debae
ID_PATH=pci-0000:00:0d.0-scsi-0:0:0:0
ID_PART_TABLE_TYPE=dos
LVM_SBIN_PATH=/sbin
UDISKS_PRESENTATION_NOPOLICY=0
UDISKS_PARTITION_TABLE=1
UDISKS_PARTITION_TABLE_SCHEME=mbr
UDISKS_PARTITION_TABLE_COUNT=2
UDISKS_ATA_SMART_IS_AVAILABLE=0
DEVLINKS=/dev/block/8:0 /dev/disk/by-id/ata-VBOX_HARDDISK_VB579a85b0-bf6debae ...
To query all information for /dev/sda:
# udevadm info --query=all --name=/dev/sda
P: /devices/pci0000:00/0000:00:0d.0/host0/target0:0:0/0:0:0:0/block/sda
N: sda
W: 37
S: block/8:0
S: disk/by-id/ata-VBOX_HARDDISK_VB579a85b0-bf6debae
S: disk/by-id/scsi-SATA_VBOX_HARDDISK_VB579a85b0-bf6debae
S: disk/by-path/pci-0000:00:0d.0-scsi-0:0:0:0
E: UDEV_LOG=3
E: DEVPATH=/devices/pci0000:00/0000:00:0d.0/host0/target0:0:0/0:0:0:0/block/sda
E: MAJOR=8
E: MINOR=0
E: DEVNAME=/dev/sda
E: DEVTYPE=disk
E: SUBSYSTEM=block
E: ID_ATA=1
E: ID_TYPE=disk
E: ID_BUS=ata
E: ID_MODEL=VBOX_HARDDISK
E: ID_MODEL_ENC=VBOX\x20HARDDISK\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20\x20...
E: ID_SERIAL=VBOX_HARDDISK_VB579a85b0-bf6debae
E: ID_SERIAL_SHORT=VB579a85b0-bf6debae
E: ID_ATA_WRITE_CACHE=1
E: ID_ATA_WRITE_CACHE_ENABLED=1
E: ID_ATA_FEATURE_SET_PM=1
E: ID_ATA_FEATURE_SET_PM_ENABLED=1
E: ID_ATA_SATA=1
E: ID_ATA_SATA_SIGNAL_RATE_GEN2=1
E: ID_SCSI_COMPAT=SATA_VBOX_HARDDISK_VB579a85b0-bf6debae
E: ID_PATH=pci-0000:00:0d.0-scsi-0:0:0:0
E: ID_PART_TABLE_TYPE=dos
E: LVM_SBIN_PATH=/sbin
E: UDISKS_PRESENTATION_NOPOLICY=0
E: UDISKS_PARTITION_TABLE=1
E: UDISKS_PARTITION_TABLE_SCHEME=mbr
E: UDISKS_PARTITION_TABLE_COUNT=2
E: UDISKS_ATA_SMART_IS_AVAILABLE=0
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Querying Udev and Sysfs
E: DEVLINKS=/dev/block/8:0 /dev/disk/by-id/ata-VBOX_HARDDISK_VB579a85b0-bf6debae ...
To display all properties of /dev/sda and its parent devices that udev has found in /sys:
# udevadm info --attribute-walk --name=/dev/sda
...
looking at device '/devices/pci0000:00/0000:00:0d.0/host0/target0:0:0/0:0:0:0/block/sda':
KERNEL=="sda"
SUBSYSTEM=="block"
DRIVER==""
ATTR{range}=="16"
ATTR{ext_range}=="256"
ATTR{removable}=="0"
ATTR{ro}=="0"
ATTR{size}=="83886080"
ATTR{alignment_offset}=="0"
ATTR{capability}=="52"
ATTR{stat}=="
20884
15437 1254282
338919
5743
8644
103994
109005 ...
ATTR{inflight}=="
0
0"
looking at parent device '/devices/pci0000:00/0000:00:0d.0/host0/target0:0:0/0:0:0:0':
KERNELS=="0:0:0:0"
SUBSYSTEMS=="scsi"
DRIVERS=="sd"
ATTRS{device_blocked}=="0"
ATTRS{type}=="0"
ATTRS{scsi_level}=="6"
ATTRS{vendor}=="ATA
"
ATTRS{model}=="VBOX HARDDISK
"
ATTRS{rev}=="1.0 "
ATTRS{state}=="running"
ATTRS{timeout}=="30"
ATTRS{iocounterbits}=="32"
ATTRS{iorequest_cnt}=="0x6830"
ATTRS{iodone_cnt}=="0x6826"
ATTRS{ioerr_cnt}=="0x3"
ATTRS{modalias}=="scsi:t-0x00"
ATTRS{evt_media_change}=="0"
ATTRS{dh_state}=="detached"
ATTRS{queue_depth}=="31"
ATTRS{queue_ramp_up_period}=="120000"
ATTRS{queue_type}=="simple"
looking at parent device '/devices/pci0000:00/0000:00:0d.0/host0/target0:0:0':
KERNELS=="target0:0:0"
SUBSYSTEMS=="scsi"
DRIVERS==""
looking at parent device '/devices/pci0000:00/0000:00:0d.0/host0':
KERNELS=="host0"
SUBSYSTEMS=="scsi"
DRIVERS==""
looking at parent device '/devices/pci0000:00/0000:00:0d.0':
KERNELS=="0000:00:0d.0"
SUBSYSTEMS=="pci"
DRIVERS=="ahci"
ATTRS{vendor}=="0x8086"
ATTRS{device}=="0x2829"
ATTRS{subsystem_vendor}=="0x0000"
ATTRS{subsystem_device}=="0x0000"
ATTRS{class}=="0x010601"
ATTRS{irq}=="21"
ATTRS{local_cpus}=="00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000003"
ATTRS{local_cpulist}=="0-1"
ATTRS{modalias}=="pci:v00008086d00002829sv00000000sd00000000bc01sc06i01"
ATTRS{numa_node}=="-1"
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Modifying Udev Rules
ATTRS{enable}=="1"
ATTRS{broken_parity_status}=="0"
ATTRS{msi_bus}==""
ATTRS{msi_irqs}==""
looking at parent device '/devices/pci0000:00':
KERNELS=="pci0000:00"
SUBSYSTEMS==""
DRIVERS==""
The command starts at the device specified by its device path and walks up the chain of parent devices.
For every device that it finds, it displays all possible attributes for the device and its parent devices in the
match key format for udev rules.
For more information, see the udevadm(8) manual page.
7.5 Modifying Udev Rules
The order in which rules are evaluated is important. Udev processes rules in lexical order. If you want to
add your own rules, you need udev to find and evaluate these rules before the default rules.
1. Create a rule file under /etc/udev/rules.d with a file name such as 10-local.rules that udev
will read before any other rules file.
For example, the following rule in 10-local.rules renames /dev/sdb to /dev/my_disk:
KERNEL=="sdb", SUBSYSTEM==“block", NAME=“my_disk”
Listing the device files in /dev shows that udev has not yet applied the rule:
# ls /dev/sd* /dev/my_disk
ls: cannot access /dev/my_disk: No such file or directory
/dev/sda /dev/sda1 /dev/sda2 /dev/sdb
2. Restart udev, use the start_udev command:
# start_udev
Starting udev:
[OK]
After Udev processes the rules files, the name of the device file has changed to /dev/my_disk:
# ls /dev/sdb* /dev/my_disk
/dev/my_disk /dev/sda /dev/sda1
/dev/sda2
To undo the changes, remove your rules file and run start_udev again.
79
80
Chapter 8 Task Management
Table of Contents
8.1 About Automating Tasks .............................................................................................................
8.2 Configuring cron Jobs .................................................................................................................
8.2.1 Controlling Access to Running cron Jobs ..........................................................................
8.3 Configuring anacron Jobs ...........................................................................................................
8.4 Running One-time Tasks .............................................................................................................
8.4.1 Changing the Behavior of Batch Jobs ...............................................................................
81
81
82
83
84
84
This chapter describes how to configure the system to run tasks automatically within a specific period of
time, at a specified time and date, or when the system is lightly loaded.
8.1 About Automating Tasks
You can use automated tasks to perform periodic backups, monitor the system, run custom scripts, and
other administrative tasks.
The cron and anacron utilities allow you to schedule the execution of recurring tasks (jobs) according
to a combination of the time, day of the month, month, day of the week, and week. cron allows you to
schedule jobs to run as often as every minute. If the system is down when a job is scheduled, cron does
not run the job when the system restarts. anacron allows you to schedule a system job to run only once
per day. However, if a scheduled job has not been run, that job runs when the system restarts. anacron is
mainly intended for use on laptop computers.
You do not usually need to run cron and anacron directly. The crond daemon executes scheduled tasks
on behalf of cron and it starts anacron once every hour. crond looks in /etc/crontab or in files in /
etc/cron.d for system cron job definitions, and /var/spool/cron for cron job definitions belonging
to users. crond checks each job definition to see whether it should run in the current minute. If a job is
scheduled for execution, crond runs it as the owner of the job definition file or, for system cron jobs, the
user specified in the job definition (if any).
crond runs the 0anacron script in the /etc/cron.hourly directory as root once per hour according
to the schedule in /etc/cron.d/0hourly. If anacron is not already running and the system is
connected to mains and not battery power, crond starts anacron.
anacron runs the scripts in the /etc/cron.daily, /etc/cron.weekly, and /etc/cron.monthly
directories as root once per day, week or month, according to the job definitions that are scheduled in /
etc/anacrontab.
8.2 Configuring cron Jobs
System cron jobs are defined in crontab-format files in /etc/crontab or in files in /etc/cron.d.
A crontab file usually consists of definitions for the SHELL, PATH, MAILTO, and HOME variables for the
environment in which the jobs run, followed by the job definitions themselves. Comment lines start with a #
character. Job definitions are specified in the following format:
minute
hour
day
month
day-of-week
user
command
where the fields are:
minute
0-59.
81
Controlling Access to Running cron Jobs
hour
0-23.
day
1-31.
month
1-12 or jan, feb,..., dec.
day-of-week
0-7 (Sunday is 0 or 7) or sun, mon,...,sat.
user
The user to run the command as, or * for the owner of the crontab file.
command
The shell script or command to be run.
For the minute through day-of week fields, you can use the following special characters:
*
(asterisk) All valid values for the field.
-
(dash) A range of integers, for example, 1-5.
,
(comma) A list of values, for example, 0,2,4.
/
(forward slash) A step value, for example, /3 in the hour field means every three hours.
For example, the following entry would run a command every five minutes on weekdays:
0-59/5
*
*
*
1-5
*
command
Run a command at one minute past midnight on the first day of the months April, June, September, and
November:
1
0
1
4,6,9,11
*
*
command
root can add job definition entries to /etc/crontab, or add crontab-format files to the /etc/cron.d
directory.
Note
If you add an executable job script to the /etc/cron.hourly directory, crond
runs the script once every hour. Your script should check that it is not already
running.
For more information, see the crontab(5) manual page.
8.2.1 Controlling Access to Running cron Jobs
If permitted, users other than root can configure cron tasks by using the crontab utility. All user-defined
crontab-format files are stored in the /var/spool/cron directory with the same name as the users that
created them.
root can use the /etc/cron.allow and /etc/cron.deny files to restrict access to cron. crontab
checks the access control files each time that a user tries to add or delete a cron job. If /etc/
cron.allow exists, only users listed in it are allowed to use cron, and /etc/cron.deny is ignored. If /
etc/cron.allow does not exist, users listed in /etc/cron.deny are not allowed to use cron. If neither
file exists, only root can use cron. The format of both /etc/cron.allow and /etc/cron.deny is one
user name on each line.
To create or edit a crontab file as a user, log in as that user and type the command crontab –e, which
opens your crontab file in the vi editor (or the editor specified by the EDITOR or VISUAL environment
82
Configuring anacron Jobs
variables). The file has the same format as /etc/crontab except that the user field is omitted. When you
save changes to the file, these are written to the file /var/spool/cron/username. To list the contents
of your crontab file, use the crontab –l command. To delete your crontab file, use the crontab -r
command.
For more information, see the crontab(1) manual page.
8.3 Configuring anacron Jobs
System anacron jobs are defined in /etc/anacrontab, which contains definitions for the SHELL, PATH,
MAILTO, RANDOM_DELAY, and START_HOURS_RANGE variables for the environment in which the jobs run,
followed by the job definitions themselves. Comment lines start with a # character.
RANDOM_DELAY is the maximum number of random time in minutes that anacron adds to the delay
parameter for a job. The default minimum delay is 6 minutes. The random offset is intended to prevent
anacron overloading the system with too many jobs at the same time.
START_HOURS_RANGE is the time range of hours during the day when anacron can run scheduled jobs.
Job definitions are specified in the following format:
period
delay
job-id
command
where the fields are:
period
Frequency of job execution specified in days or as @daily, @weekly, or @monthly for once
per day, week, or month.
delay
Number of minutes to wait before running a job.
job-id
Unique name for the job in log files.
command
The shell script or command to be run.
The following entries are taken from the default /etc/anacrontab file:
SHELL=/bin/sh
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
# the maximal random delay added to the base delay of the jobs
RANDOM_DELAY=45
# the jobs will be started during the following hours only
START_HOURS_RANGE=3-22
#period in days
1
7
@monthly
delay in minutes job-identifier
command
5
cron.daily
nice run-parts /etc/cron.daily
25
cron.weekly
nice run-parts /etc/cron.weekly
45
cron.monthly
nice run-parts /etc/cron.monthly
By default, anacron runs jobs between 03:00 and 22:00 and randomly delays jobs by between 11 and 50
minutes. The job scripts in /etc/cron.daily, run anywhere between 03:11 and 03:50 every day if the
system is running, or after the system is booted and the time is less than 22:00. The run-parts script
sequentially executes every program within the directory specified as its argument.
Scripts in /etc/cron.weekly run once per week with a delay offset of between 31 and 70 minutes.
Scripts in /etc/cron.monthly run once per week with a delay offset of between 51 and 90 minutes.
For more information, see the anacron(8) and anacrontab(5) manual pages.
83
Running One-time Tasks
8.4 Running One-time Tasks
You can use the at command to schedule a one-time task to run at a specified time, or the batch
command to schedule a one-time task to run when the system load average drops below 0.8. The atd
service must be running to use at or batch.
# service atd status
atd (pid 2078) is running...
at takes a time as its argument and reads the commands to be run from the standard input. For example,
run the commands in the file atjob in 20 minutes time:
# at now + 20 minutes < ./atjob
job 1 at 2013-03-19 11:25
The atq command shows the at jobs that are queued to run:
# atq
1 2013-03-19 11:25 a root
The batch command also reads command from the standard input, but it does not run until the system
load average drops below 0.8. For example:
# batch < batchjob
job 2 at 2013-03-19 11:31
To cancel one or more queued jobs, specify their job numbers to the atrm command, for example:
# atrm 1 2
For more information, see the at(1) manual page.
8.4.1 Changing the Behavior of Batch Jobs
The load average of a system, as displayed by the uptime and w commands, represents the average
number of processes that are queued to run on the CPUs or CPU cores over a given time period. Typically,
a system might not considered overloaded until the load average exceeds 0.8 times the number of CPUs
or CPU cores. On such systems, you would usually want atd to be able to run batch jobs when the load
average drops below the number of CPUs or CPU cores, rather than the default limit of 0.8. For example,
on a system with 4 CPU cores, you could set the load-average limit above which atd will not run batch
jobs to 3.2.
If you know that a batch job typically takes more than a minute to run, you can also change the minimum
interval that atd waits between starting batch jobs. The default minimum interval is 60 seconds.
To change the load-average limit and interval time for batch jobs:
1. Edit /etc/init.d/atd, and add a line that defines the new load-average limit, minimum interval, or
both in the OPTS variable for the atd daemon, for example:
exec=/usr/sbin/atd
OPTS="-b 120 -l 3.2"
prog="atd"
This example sets the minimum interval to 120 seconds and the load-average limit to 3.2.
2. Restart the atd service:
# service atd restart
84
Changing the Behavior of Batch Jobs
Stopping atd:
Starting atd:
[
[
OK
OK
]
]
3. Verify that the atd daemon is running with the new minimum interval and load-average limit:
# ps -fC atd
UID
PID
root
8359
PPID
1
C STIME TTY
0 12:06 ?
TIME CMD
00:00:00 /usr/sbin/atd -b 120 -l 3.2
For more information, see the atd(3) manual page.
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Chapter 9 System Monitoring and Tuning
Table of Contents
9.1 About sosreport ..........................................................................................................................
9.1.1 Configuring and Using sosreport .......................................................................................
9.2 About System Performance Tuning .............................................................................................
9.2.1 About Performance Problems ...........................................................................................
9.2.2 Monitoring Usage of System Resources ............................................................................
9.2.3 Using the Graphical System Monitor .................................................................................
9.2.4 About OSWatcher Black Box ............................................................................................
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89
92
92
This chapter describes how to collect diagnostic information about a system for Oracle Support, and how to
monitor and tune the performance of a system.
9.1 About sosreport
The sosreport utility collects information about a system such as hardware configuration, software
configuration, and operational state. You can also use sosreport to enable diagnostics and analytical
functions. To assist in troubleshooting a problem, sosreport records the information in a compressed file
that you can send to a support representative.
9.1.1 Configuring and Using sosreport
If the sos package is not already installed on your system, use yum to install it.
Use the following command to list the available plugins and plugin options.
# sosreport –l
The following plugins are currently enabled:
acpid
acpid related information
anaconda
Anaconda / Installation information
.
.
.
The following plugins are currently disabled:
amd
Amd automounter information
cluster
cluster suite and GFS related information
.
.
.
The following plugin options are available:
apache.log
off gathers all apache logs
auditd.syslogsize
15 max size (MiB) to collect per syslog file
.
.
.
See the sosreport(1) manual page for information about how to enable or disable plugins, and how to
set values for plugin options.
To run sosreport:
1. Enter the command, specifying any options that you need to tailor the report to report information about
a problem area.
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About System Performance Tuning
# sosreport [options ...]
For example, to record only information about Apache and Tomcat, and to gather all the Apache logs:
# sosreport -o apache,tomcat -k apache.log=on
sosreport (version 2.2)
.
.
.
Press ENTER to continue, or CTRL-C to quit.
To enable all boolean options for all loaded plugins except the rpm.rpmva plugin that verifies all
packages, and which takes a considerable time to run:
# sosreport -a -k rpm.rpmva=off
2. Type Enter, and enter additional information when prompted.
Please enter your first initial and last name [email_address]: AName
Please enter the case number that you are generating this report for: case#
Running plugins. Please wait ...
Completed [55/55] ...
Creating compressed archive...
Your sosreport has been generated and saved in:
/tmp/sosreport-AName.case#-datestamp-ID.tar.xz
The md5sum is: checksum
Please send this file to your support representative.
sosreport saves the report as an xz-compressed tar file in /tmp.
For more information, see the sosreport(1) manual page.
9.2 About System Performance Tuning
Performance issues can be caused by any of a system's components, software or hardware, and by their
interaction. Many performance diagnostics utilities are available for Oracle Linux, including tools that
monitor and analyze resource usage by different hardware components and tracing tools for diagnosing
performance issues in multiple processes and their threads.
9.2.1 About Performance Problems
Many performance issues are the result of configuration errors. You can avoid such errors by using a
validated configuration that has been pre-tested fore the supported software, hardware, storage, drivers,
and networking components. A validated configuration incorporates the best practices for Oracle Linux
deployment and has undergone real-world testing of the complete stack. Oracle publishes more than 100
validated configurations, which are freely available for download. You should also refer to the release notes
for recommendations on setting kernel parameters.
A typical problem involves out of memory errors and generally poor performance when running Oracle
Database. The cause of this problem is likely to be that the system is not configured to use the HugePages
feature for the System Global Area (SGA). With HugePages, you can set the page size to between
2MB and 256MB, so reducing the total number of pages that the kernel needs to manage. The memory
associated with HugePages cannot be swapped out, which forces the SGA to remain resident in memory.
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Monitoring Usage of System Resources
The following utilities allow you to collect information about system resource usage and errors, and can
help you to identify performance problems caused by overloaded disks, network, memory, or CPUs:
dmesg
Displays the contents of the kernel ring buffer, which can contain errors about system resource
usage. Provided by the util-linux-ng package.
dstat
Displays statistics about system resource usage. Provided by the dstat package.
free
Displays the amount of free and used memory in the system. Provided by the procps package.
iostat
Reports I/O statistics. Provided by the sysstat package.
iotop
Monitors disk and swap I/O on a per-process basis. Provided by the iotop package.
ip
Reports network interface statistics and errors. Provided by the iproute package.
mpstat
Reports processor-related statistics. Provided by the sysstat package.
sar
Reports information about system activity. Provided by the sysstat package.
ss
Reports network interface statistics. Provided by the iproute package.
top
Provides a dynamic real-time view of the tasks that are running on a system. Provided by the
procps package.
uptime
Displays the system load averages for the past 1, 5, and 15 minutes. Provided by the procps
package.
vmstat
Reports virtual memory statistics. Provided by the procps package.
Many of these utilities provide overlapping functionality. For more information, see the individual manual
page for the utility.
See Section 5.2.3, “Parameters that Control System Performance” for a list of kernel parameters that affect
system performance.
9.2.2 Monitoring Usage of System Resources
You need to collect and monitor system resources regularly to provide you with a continuous record of a
system. Establish a baseline of acceptable measurements under typical operating conditions. You can then
use the baseline as a reference point to make it easier to identify memory shortages, spikes in resource
usage, and other problems when they occur. Monitoring system performance also allows you to plan for
future growth and to see how configuration changes might affect future performance.
To run a monitoring command every interval seconds in real time and watch its output change, use the
watch command. For example, the following command runs the mpstat command once per second:
# watch -n interval mpstat
Alternatively, many of the commands allow you to specify the sampling interval in seconds, for example:
# mpstat interval
If installed, the sar command records statistics every 10 minutes while the system is running and retains
this information for every day of the current month. The following command displays all the statistics that
sar recorded for day DD of the current month:
# sar -A -f /var/log/sa/saDD
To run sar command as a background process and collect data in a file that you can display later by using
the -f option:
89
Monitoring Usage of System Resources
# sar -o datafile interval count >/dev/null 2>&1 &
where count is the number of samples to record.
Oracle OSWatcher Black Box (OSWbb) and OSWbb analyzer (OSWbba) are useful tools for collecting and
analysing performance statistics. For more information, see Section 9.2.4, “About OSWatcher Black Box”.
9.2.2.1 Monitoring CPU Usage
The uptime, mpstat, sar, dstat, and top utilities allow you to monitor CPU usage. When a system's
CPU cores are all occupied executing the code of processes, other processes must wait until a CPU core
becomes free or the scheduler switches a CPU core to run their code. If too many processes are queued
too often, this can represent a bottleneck in the performance of the system.
The commands mpstat -P ALL and sar -u -P ALL display CPU usage statistics for each CPU core
and averaged across all CPU cores.
The %idle value shows the percentage of time that a CPU was not running system code or process code.
If the value of %idle is near 0% most of the time on all CPU cores, the system is CPU-bound for the
workload that it is running. The percentage of time spent running system code (%systemor %sys) should
not usually exceed 30%, especially if %idle is close to 0%.
The system load average represents the number of processes that are running on CPU cores, waiting to
run, or waiting for disk I/O activity to complete averaged over a period of time. On a busy system, the load
average reported by uptime or sar -q should usually be not greater than two times the number of CPU
cores over periods as long as 5 or 15 minutes. If the load average exceeds four times the number of CPU
cores for long periods, the system is overloaded.
In addition to load averages (ldavg-*), the sar -q command reports the number of processes currently
waiting to run (the run-queue size, runq-sz) and the total number of processes (plist_sz). The value of
runq-sz also provides an indication of CPU saturation.
Determine the system's average load under normal loads where users and applications do not experience
problems with system responsiveness, and then look for deviations from this benchmark over time. A
dramatic rise in the load average can indicate a serious performance problem.
A combination of sustained large load average or large run queue size and low %idle can indicate that the
system has insufficient CPU capacity for the workload. When CPU usage is high, use a command such as
dstat or top to determine which processes are most likely to be responsible. For example, the following
dstat command shows which processes are using CPUs, memory, and block I/O most intensively:
# dstat --top-cpu --top-mem --top-bio
The top command provides a real-time display of CPU activity. By default, top lists the most CPUintensive processes on the system. In its upper section, top displays general information including the load
averages over the past 1, 5 and 15 minutes, the number of running and sleeping processes (tasks), and
total CPU and memory usage. In its lower section, top displays a list of processes, including the process
ID number (PID), the process owner, CPU usage, memory usage, running time, and the command name.
By default, the list is sorted by CPU usage, with the top consumer of CPU listed first. Type f to select
which fields top displays, o to change the order of the fields, or O to change the sort field. For example,
entering On sorts the list on the percentage memory usage field (%MEM).
9.2.2.2 Monitoring Memory Usage
The sar -r command reports memory utilization statistics, including %memused, which is the percentage
of physical memory in use.
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Monitoring Usage of System Resources
sar -B reports memory paging statistics, including pgscank/s, which is the number of memory pages
scanned by the kswapd daemon per second, and pgscand/s, which is the number of memory pages
scanned directly per second.
sar -W reports swapping statistics, including pswpin/s and pswpout/s, which are the numbers of
pages per second swapped in and out per second.
If %memused is near 100% and the scan rate is continuously over 200 pages per second, the system has a
memory shortage.
Once a system runs out of real or physical memory and starts using swap space, its performance
deteriorates dramatically. If you run out of swap space, your programs or the entire operating system are
likely to crash. If free or top indicate that little swap space remains available, this is also an indication
you are running low on memory.
The output from the dmesg command might include notification of any problems with physical memory that
were detected at boot time.
9.2.2.3 Monitoring Block I/O Usage
The iostat command monitors the loading of block I/O devices by observing the time that the devices
are active relative to the average data transfer rates. You can use this information to adjust the system
configuration to balance the I/O loading across disks and host adapters.
iostat -x reports extended statistics about block I/O activity at one second intervals, including %util,
which is the percentage of CPU time spent handling I/O requests to a device, and avgqu-sz, which is
the average queue length of I/O requests that were issued to that device. If %util approaches 100% or
avgqu-sz is greater than 1, device saturation is occurring.
You can also use the sar -d command to report on block I/O activity, including values for %util and
avgqu-sz.
The iotop utility can help you identify which processes are responsible for excessive disk I/O. iotop has
a similar user interface to top. In its upper section, iotop displays the total disk input and output usage in
bytes per second. In its lower section, iotop displays I/O information for each process, including disk input
output usage in bytes per second, the percentage of time spent swapping in pages from disk or waiting
on I/O, and the command name. Use the left and right arrow keys to change the sort field, and press A to
toggle the I/O units between bytes per second and total number of bytes, or O to toggle between displaying
all processes or only those processes that are performing I/O.
9.2.2.4 Monitoring File System Usage
The sar -v command reports the number of unused cache entries in the directory cache (dentunusd)
and the numbers of in-use file handles (file-nr), inode handlers (inode-nr), and pseudo terminals
(pty-nr).
iostat -n reports I/O statistics for each NFS file system that is mounted.
9.2.2.5 Monitoring Network Usage
The ip -s link command displays network statistics and errors for all network devices, including
the numbers of bytes transmitted (TX) and received (RX). The dropped and overrun fields provide an
indicator of network interface saturation.
The ss -s command displays summary statistics for each protocol.
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Using the Graphical System Monitor
9.2.3 Using the Graphical System Monitor
The GNOME desktop environment includes a graphical system monitor that allows you to display
information about the system configuration, running processes, resource usage, and file systems.
To display the System Monitor, use the following command:
# gnome-system-monitor
The Resources tab displays:
• CPU usage history in graphical form and the current CPU usage as a percentage.
• Memory and swap usage history in graphical form and the current memory and swap usage.
• Network usage history in graphical form, the current network usage for reception and transmission, and
the total amount of data received and transmitted.
To display the System Monitor Manual, press F1 or select Help > Contents.
9.2.4 About OSWatcher Black Box
Oracle OSWatcher Black Box (OSWbb) collects and archives operating system and network metrics that
you can use to diagnose performance issues. OSWbb operates as a set of background processes on the
server and gathers data on a regular basis, invoking such Unix utilities as vmstat, mpstat, netstat,
iostat, and top.
OSWbb is particularly useful for Oracle RAC (Real Application Clusters) and Oracle Grid Infrastructure
configurations. The RAC-DDT (Diagnostic Data Tool) script file includes OSWbb, but does not install it by
default.
9.2.4.1 Installing OSWbb
To install OSWbb:
1. Log on to My Oracle Support (MOS) at http://support.oracle.com.
2. Download OSWatcher from the link listed by Doc ID 301137.1 at https://support.oracle.com/epmos/
faces/DocumentDisplay?id=301137.1.
3. Copy the file to the directory where you want to install OSWbb, and run the following command:
# tar xvf oswbbVERS.tar
VERS represents the version number of OSWatcher, for example 730 for OSWatcher 7.30.
Extracting the tar file creates a directory named oswbb, which contains all the directories and files that
are associated with OSWbb, including the startOSWbb.sh script.
4. To enable the collection of iostat information for NFS volumes, edit the OSWatcher.sh script in the
oswbb directory, and set the value of nfs_collect to 1:
nfs_collect=1
9.2.4.2 Running OSWbb
To start OSWbb, run the startOSWbb.sh script from the oswbb directory.
# ./startOSWbb.sh [frequency duration]
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About OSWatcher Black Box
The optional frequency and duration arguments specifying how often in seconds OSWbb should collect
data and the number of hours for which OSWbb should run. The default values are 30 seconds and 48
hours. The following example starts OSWbb recording data at intervals of 60 seconds, and has it record
data for 12 hours:
# ./startOSWbb.sh 60 12
...
Testing for discovery of OS Utilities...
VMSTAT found on your system.
IOSTAT found on your system.
MPSTAT found on your system.
IFCONFIG found on your system.
NETSTAT found on your system.
TOP found on your system.
Testing for discovery of OS CPU COUNT
oswbb is looking for the CPU COUNT on your system
CPU COUNT will be used by oswbba to automatically look for cpu problems
CPU COUNT found on your system.
CPU COUNT = 4
Discovery completed.
Starting OSWatcher Black Box v7.3.0 on date and time
With SnapshotInterval = 60
With ArchiveInterval = 12
...
Data is stored in directory: OSWbba_archive
Starting Data Collection...
oswbb heartbeat: date and time
oswbb heartbeat: date and time + 60 seconds
...
OSWbba_archive is the path of the archive directory that contains the OSWbb log files.
To stop OSWbb prematurely, run the stopOSWbb.sh script from the oswbb directory.
# ./stopOSWbb.sh
OSWbb collects data in the following directories under the oswbb/archive directory:
Directory
Description
oswiostat
Contains output from the iostat utility.
oswmeminfo
Contains a listing of the contents of /proc/meminfo.
oswmpstat
Contains output from the mpstat utility.
oswnetstat
Contains output from the netstat utility.
oswprvtnet
If you have enable private network tracing for RAC, contains information about the
status of the private networks.
oswps
Contains output from the ps utility.
oswslabinfo
Contains a listing of the contents of /proc/slabinfo.
oswtop
Contains output from the top utility.
oswvmstat
Contains output from the vmstat utility.
OSWbb stores data in hourly archive files named system_name_utility_name_timestamp.dat.
Each entry in a file is preceded by a timestamp.
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About OSWatcher Black Box
9.2.4.3 Analysing OSWbb Archived Files
From release v4.0.0, you can use the OSWbb analyzer (OSWbba) to provide information on system
slowdowns, system hangs and other performance problems, and also to graph data collected from
iostat, netstat, and vmstat. OSWbba requires that you have installed Java version 1.4.2 or higher
on your system. You can use yum to install Java, or you can download a Java RPM for Linux from http://
www.java.com.
Use the following command to run OSWbba from the oswbb directory:
# java -jar oswbba.jar -i OSWbba_archive
OSWbba_archive is the path of the archive directory that contains the OSWbb log files.
You can use OSWbba to display the following types of performance graph:
• Process run, wait and block queues.
• CPU time spent running in system, user, and idle mode.
• Context switches and interrupts.
• Free memory and available swap.
• Reads per second, writes per second, service time for I/O requests, and percentage utilization of
bandwidth for a specified block device.
You can also use OSWbba to save the analysis to a report file, which reports instances of system
slowdown,spikes in run queue length, or memory shortage, describes probable causes, and offers
suggestions of how to improve performance.
# java -jar oswbba.jar -i OSWbba_archive -A
For more information about OSWbb and OSWbba, refer to the OSWatcher Black Box User Guide (Article
ID 301137.1) and the OSWatcher Black Box Analyzer User Guide (Article ID 461053.1), which are
available from My Oracle Support (MOS) at http://support.oracle.com.
94
Chapter 10 System Dump Analysis
Table of Contents
10.1 About Kdump ............................................................................................................................ 95
10.1.1 Configuring and Using Kdump ........................................................................................ 95
10.1.2 Files Used by Kdump ..................................................................................................... 97
10.1.3 Using Kdump with OCFS2 .............................................................................................. 97
10.1.4 Using Kdump with a System Hang .................................................................................. 98
10.2 Using the crash Debugger ......................................................................................................... 98
10.2.1 Installing the crash Packages ......................................................................................... 98
10.2.2 Running crash ................................................................................................................ 99
10.2.3 Kernel Data Structure Analysis Commands ................................................................... 100
10.2.4 System State Commands ............................................................................................. 102
10.2.5 Helper Commands ....................................................................................................... 105
10.2.6 Session Control Commands .......................................................................................... 105
10.2.7 Guidelines for Examining a Dump File ........................................................................... 106
This chapter describes how to configure a system to create a memory image in the event of a system
crash, and how to use the crash debugger to analyse the memory image in a crash dump or for a live
system.
10.1 About Kdump
Kdump is the Linux kernel crash-dump mechanism. Oracle recommends that you enable the Kdump
feature. In the event of a system crash, Kdump creates a memory image (vmcore) that can help in
determining the cause of the crash. Enabling Kdump requires you to reserve a portion of system memory
for exclusive use by Kdump. This memory is unavailable for other uses.
Kdump uses kexec to boot into a second kernel whenever the system crashes. kexec is a fast-boot
mechanism which allows a Linux kernel to boot from inside the context of a kernel that is already running
without passing through the bootloader stage.
10.1.1 Configuring and Using Kdump
During installation, you are given the option of enabling Kdump and specifying the amount of memory to
reserve for it. If you prefer, you can enable kdump at a later time as described in this section.
If the kexec-tools and system-config-kdump packages are not already installed on your system,
use yum to install them.
To enable Kdump by using the Kernel Dump Configuration GUI.
1. Enter the following command.
# system-config-kdump
The Kernel Dump Configuration GUI starts. If Kdump is currently disabled, the green Enable button is
selectable and the Disable button is greyed out.
2. Click Enable to enable Kdump.
3. You can select the following settings tags to adjust the configuration of Kdump.
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Configuring and Using Kdump
Basic Settings
Allows you to specify the amount of memory to reserve for Kdump. The
default setting is 128 MB.
Target Settings
Allows you to specify the target location for the vmcore dump file on
a locally accessible file system, to a raw disk device, or to a remote
directory using NFS or SSH over IPv4. The default location is /var/
crash.
You cannot save a dump file on an eCryptfs file system, on remote
directories that are NFS mounted on the rootfs file system, or on
remote directories that access require the use of IPv6, SMB, CIFS, FCoE,
wireless NICs, multipathed storage, or iSCSI over software initiators to
access them.
Filtering Settings
Allows to select which type of data to include in or exclude from the dump
file. Selecting or deselecting the options alters the value of the argument
that Kdump specifies to the -d option of the core collector program,
makedumpfile.
Expert Settings
Allows you to choose which kernel to use, edit the command line options
that are passed to the kernel and the core collector program, choose
the default action if the dump fails, and modify the options to the core
collector program, makedumpfile.
For example, if Kdump fails to start, and the following error appears
in /var/log/messages, set the offset for the reserved memory
to 48 MB or greater in the command line options, for example
[email protected]:
kdump: No crashkernel parameter specified for running kernel
The Unbreakable Enterprise Kernel supports the use of the
crashkernel=auto setting for UEK Release 3 Quarterly Update 1
and later. If you use the crashkernel=auto setting, the output of the
dmesg command shows [email protected], which is normal. The
setting actually reserves 128 MB plus 64 MB for each terabyte of physical
memory.
Note
You cannot configure crashkernel=auto
for Xen or for the UEK prior to UEK Release
3 Quarterly Update 1. Only standard settings
such as [email protected] are
supported. For systems with more than 128
GB of memory, the recommended setting is
[email protected]
You can select one of five default actions should the dump fail:
mount rootfs and run /sbin/
init
96
Mount the root file system and run
init. The /etc/init.d/kdump
script attempts to save the dump to /
var/crash, which requires a large
amount of memory to be reserved.
Files Used by Kdump
reboot
Reboot the system, losing the vmcore.
This is the default action.
shell
Enter a shell session inside the
initramfs so that you can attempt to
record the core. To reboot the system,
exit the shell.
halt
Halt the system.
poweroff
Power down the system.
Click Help for more information on these settings.
4. Click Apply to save your changes. The GUI displays a popup message to remind you that you must
reboot the system for the changes to take effect.
5. Click OK to dismiss the popup messages.
6. Select File > Quit.
7. Reboot the system at a suitable time.
10.1.2 Files Used by Kdump
The Kernel Dump Configuration GUI modifies the following files:
File
Description
/boot/grub/grub.conf
Appends the crashkernel option to the kernel line to specify the
amount of reserved memory and any offset value.
/etc/kdump.conf
Sets the location where the dump file can be written, the filtering level
for the makedumpfile command, and the default behavior to take if
the dump fails. See the comments in the file for information about the
supported parameters.
If you edit these files, you must reboot the system for the changes to take effect.
For more information, see the kdump.conf(5) manual page.
10.1.3 Using Kdump with OCFS2
By default, a fenced node in an OCFS2 cluster restarts instead of panicking so that it can quickly rejoin the
cluster. If the reason for the restart is not apparent, you can change the node's behavior so that it panics
and generates a vmcore for analysis.
To configure a node to panic when it next fences, run the following command on the node after the cluster
starts:
# echo panic > /sys/kernel/config/cluster/cluster_name/fence_method
where cluster_name is the name of the cluster. To set the value after each reboot of the system, add
this line to /etc/rc.local. To restore the default behavior, set the value of fence_method to reset
instead of panic and remove the line from /etc/rc.local.
For more information, see Section 21.3.5, “Configuring the Behavior of Fenced Nodes”.
97
Using Kdump with a System Hang
10.1.4 Using Kdump with a System Hang
To allow you to troubleshoot an issue where any user or kernel thread sleeps in the
TASK_UNINTERRUPTIBLE state (D state) for more than the time interval defined by the parameter
kernel.hung_task_timeout_secs, use sysctl to set the value of kernel.hung_task_panic to 1
so that the system panics and generates a vmcore for analysis.
# sysctl -w kernel.hung_task_panic=1
kernel.hung_task_panic = 1
The setting remains in force only until the system is rebooted. To make the setting persist after the system
is rebooted, add it to the /etc/sysctl.conf file. To restore the default behavior, set the value of
kernel.hung_task_panic to 0.
For more information, see Section 5.2.2, “Changing Kernel Parameters” and Section 5.2.4, “Parameters
that Control Kernel Panics”.
10.2 Using the crash Debugger
The crash utility allows you to analyze the state of the Oracle Linux system while it is running or of a core
dump that resulted from a kernel crash. crash has been merged with the GNU Debugger gdb to provide
source code debugging capabilities.
10.2.1 Installing the crash Packages
To use crash, you must install the crash package and the appropriate debuginfo and debuginfocommon packages.
To install the required packages:
1. Install the latest version of the crash package:
# yum install crash
2. Download the appropriate debuginfo and debuginfo-common packages for the vmcore or kernel
that you want to examine from https://oss.oracle.com/ol6/debuginfo/:
• If you want to examine the running Unbreakable Enterprise Kernel on the system, use commands
such as the following to download the packages:
# export DLP="https://oss.oracle.com/ol6/debuginfo"
# wget ${DLP}/kernel-uek-debuginfo-`uname -r`.rpm
# wget ${DLP}/kernel-uek-debuginfo-common-`uname -r`.rpm
• If you want to examine the running Red Hat Compatible Kernel on the system, use commands such
as the following to download the packages:
# export DLP="https://oss.oracle.com/ol6/debuginfo"
# wget ${DLP}/kernel-debuginfo-`uname -r`.rpm
# wget ${DLP}/kernel-debuginfo-common-`uname -r`.rpm
• If you want to examine a vmcore file that relates to a different kernel than is currently running,
download the appropriate debuginfo and debuginfo-common packages for the kernel that
produce the vmcore, for example:
# export DLP="https://oss.oracle.com/ol6/debuginfo"
# wget ${DLP}/kernel-uek-debuginfo-2.6.32-300.27.1.el6uek.x86_64.rpm
# wget ${DLP}/kernel-uek-debuginfo-common-2.6.32-300.27.1.el6uek.x86_64.rpm
98
Running crash
Note
If the vmcore file was produced by Kdump, you can use the following crash
command to determine the version:
# crash --osrelease /var/tmp/vmcore/2013-0211-2358.45-host03.28.core
2.6.39-200.24.1.el6uek.x86_64
3. Install the debuginfo and debuginfo-common packages, for example:
# rpm -Uhv kernel-uek-debuginfo-2.6.32-300.27.1.el6uek.x86_64.rpm \
kernel-uek-debuginfo-common-2.6.32-300.27.1.el6uek.x86_64.rpm
The vmlinux kernel object file (also known as the namelist file) that crash requires is installed in /
usr/lib/debug/lib/modules/kernel_version/.
10.2.2 Running crash
Warning
Running crash on a live system is dangerous and can cause data corruption or
total system failure. Do not use crash to examine a production system unless so
directed by Oracle Support.
To examine the currently running kernel:
# crash
To determine the version of the kernel that produced a vmcore file:
# crash --osrelease /var/tmp/vmcore/2013-0211-2358.45-host03.28.core
2.6.39-200.24.1.el6uek.x86_64
To examine a vmcore file, specify the path to the file as an argument, for example:
# crash /var/tmp/vmcore/2013-0211-2358.45-host03.28.core
The appropriate vmlinux file must exist in /usr/lib/debug/lib/modules/kernel_version/.
If the vmlinux file is located elsewhere, specify its path before the path to the vmcore file, for example:
# crash /var/tmp/namelist/vmlinux-host03.28 /var/tmp/vmcore/2013-0211-2358.45-host03.28.core
The following crash output is from a vmcore file that was dumped after a system panic:
KERNEL:
DUMPFILE:
CPUS:
DATE:
UPTIME:
LOAD AVERAGE:
TASKS:
NODENAME:
RELEASE:
VERSION:
MACHINE:
MEMORY:
PANIC:
PID:
COMMAND:
/usr/lib/debug/lib/modules/2.6.39-200.24.1.el6uek.x86_64/vmlinux
/var/tmp/vmcore/2013-0211-2358.45-host03.28.core
2
Fri Feb 11 16:55:41 2013
04:24;54
0.00, 0.01, 0.05
84
host03.mydom.com
2.6.39-200.24.1.el6uek.x86_64
#1 SMP Sat Jun 23 02:39:07 EDT 2012
x86_64 (2992 MHz)
2 GB
"Oops: 0002" (check log for details)
1696
"insmod“
99
Kernel Data Structure Analysis Commands
TASK: c74de000
CPU: 0
STATE: TASK_RUNNING (PANIC)
crash>
The output includes the number of CPUs, the load average over the last 1 minute, last 5 minutes, and
last 15 minutes, the number of tasks running, the amount of memory, the panic string, and the command
that was executing at the time the dump was created. In this example, an attempt by insmod to install a
module resulted in an oops violation.
At the crash> prompt, you can enter help or ? to display the available crash commands. Enter help
command to display more information for a specified command.
crash commands can be grouped into several different groups according to purpose:
Kernel Data Structure Analysis
Commands
Display kernel text and data structures. See Section 10.2.3, “Kernel
Data Structure Analysis Commands”.
System state commands
Examine kernel subsystems on a system-wide or a per-task basis. See
Section 10.2.4, “System State Commands”.
Helper commands
Perform calculation, translation, and search functions. See
Section 10.2.5, “Helper Commands”
Session control commands
Control the crash session. See Section 10.2.6, “Session Control
Commands”
For more information, see the crash(8) manual page.
10.2.3 Kernel Data Structure Analysis Commands
The following crash commands takes advantage of gdb integration to display kernel data structures
symbolically:
*
The pointer-to command can be used instead struct or union. The gdb module calls the
appropriate function. For example:
crash> *buffer_head
struct buffer_head {
long unsigned int b_state;
struct buffer_head *b_this_page;
struct page *b_page;
sector_t b_blocknr;
size_t b_size;
char *b_data;
struct block_device *b_bdev;
bh_end_io_t *b_end_io;
void *b_private;
struct list_head b_assoc_buffers;
struct address_space *b_assoc_map;
atomic_t b_count;
}
SIZE: 104
dis
Disassembles source code instructions of a complete kernel function, from a specified address
for a specified number of instructions, or from the beginning of a function up to a specified
address. For example:
crash> dis fixup_irqs
100
Kernel Data Structure Analysis Commands
0xffffffff81014486
0xffffffff81014487
0xffffffff8101448a
0xffffffff8101448c
0xffffffff8101448e
0xffffffff81014490
0xffffffff81014492
0xffffffff81014493
0xffffffff81014497
...
p
<fixup_irqs>:
<fixup_irqs+1>:
<fixup_irqs+4>:
<fixup_irqs+6>:
<fixup_irqs+8>:
<fixup_irqs+10>:
<fixup_irqs+12>:
<fixup_irqs+13>:
<fixup_irqs+17>:
push
mov
push
push
push
push
push
sub
nopl
%rbp
%rsp,%rbp
%r15
%r14
%r13
%r12
%rbx
$0x18,%rsp
0x0(%rax,%rax,1)
Displays the contents of a kernel variable. For example:
crash> p init_mm
init_mm = $5 = {
mmap = 0x0,
mm_rb = {
rb_node = 0x0
},
mmap_cache = 0x0,
get_unmapped_area = 0,
unmap_area = 0,
mmap_base = 0,
task_size = 0,
cached_hole_size = 0,
free_area_cache = 0,
pgd = 0xffffffff81001000,
...
struct
Displays either a structure definition, or a formatted display of the contents of a structure at a
specified address. For example:
crash> struct cpu
struct cpu {
int node_id;
int hotpluggable;
struct sys_device sysdev;
}
SIZE: 88
sym
Translates a kernel symbol name to a kernel virtual address and section, or a kernel virtual
address to a symbol name and section. You can also query (-q) the symbol list for all symbols
containing a specified string or list (-l) all kernel symbols. For example:
crash> sym jiffies
ffffffff81b45880 (A) jiffies
crash> sym -q runstate
c590 (d) per_cpu__runstate
c5c0 (d) per_cpu__runstate_snapshot
ffffffff8100e563 (T) xen_setup_runstate_info
crash> sym -l
0 (D) __per_cpu_start
0 (D) per_cpu__irq_stack_union
4000 (D) per_cpu__gdt_page
5000 (d) per_cpu__exception_stacks
b000 (d) per_cpu__idt_desc
b010 (d) per_cpu__xen_cr0_value
b018 (D) per_cpu__xen_vcpu
b020 (D) per_cpu__xen_vcpu_info
b060 (d) per_cpu__mc_buffer
c570 (D) per_cpu__xen_mc_irq_flags
c578 (D) per_cpu__xen_cr3
c580 (D) per_cpu__xen_current_cr3
c590 (d) per_cpu__runstate
c5c0 (d) per_cpu__runstate_snapshot
...
101
System State Commands
union
Similar to the struct command, displaying kernel data types that are defined as unions instead
of structures.
whatis
Displays the definition of structures, unions, typedefs or text or data symbols. For example:
crash> whatis linux_binfmt
struct linux_binfmt {
struct list_head lh;
struct module *module;
int (*load_binary)(struct linux_binprm *, struct pt_regs *);
int (*load_shlib)(struct file *);
int (*core_dump)(long int, struct pt_regs *, struct file *, long unsigned int);
long unsigned int min_coredump;
int hasvdso;
}
SIZE: 64
10.2.4 System State Commands
The following commands display kernel subsystems on a system-wide or per-task basis:
bt
Displays a kernel stack trace of the current context or of a specified PID or task. In the case of a
dump that followed a kernel panic, the command traces the functions that were called leading up
to the panic. For example:
crash> bt
PID: 10651 TASK: d1347000 CPU: 1
COMMAND: "insmod"
#0 [d1547e44] die at c010785a
#1 [d1547e54] do_invalid_op at c0107b2c
#2 [d1547f0c] error_code (via invalid_op) at c01073dc
...
You can use the –l option to display the line number of the source file that corresponds to each
function call in a stack trace.
crash> bt -l 1
PID: 1
TASK: ffff88007d032040 CPU: 1
COMMAND: "init"
#0 [ffff88007d035878] schedule at ffffffff8144fdd4
/usr/src/debug/kernel-2.6.32/linux-2.6.32.x86_64/kernel/sched.c: 3091
#1 [ffff88007d035950] schedule_hrtimeout_range at ffffffff814508e4
/usr/src/debug/kernel-2.6.32/linux-2.6.32.x86_64/arch/x86/include/asm/current.h: 14
#2 [ffff88007d0359f0] poll_schedule_timeout at ffffffff811297d5
/usr/src/debug/kernel-2.6.32/linux-2.6.32.x86_64/arch/x86/include/asm/current.h: 14
#3 [ffff88007d035a10] do_select at ffffffff81129d72
/usr/src/debug/kernel-2.6.32/linux-2.6.32.x86_64/fs/select.c: 500
#4 [ffff88007d035d80] core_sys_select at ffffffff8112a04c
/usr/src/debug/kernel-2.6.32/linux-2.6.32.x86_64/fs/select.c: 575
#5 [ffff88007d035f10] sys_select at ffffffff8112a326
/usr/src/debug/kernel-2.6.32/linux-2.6.32.x86_64/fs/select.c: 615
#6 [ffff88007d035f80] system_call_fastpath at ffffffff81011cf2
/usr/src/debug////////kernel-2.6.32/linux-2.6.32.x86_64/arch/x86/kernel/entry_64.S:
488
RIP: 00007fce20a66243 RSP: 00007fff552c1038 RFLAGS: 00000246
RAX: 0000000000000017 RBX: ffffffff81011cf2 RCX: ffffffffffffffff
RDX: 00007fff552c10e0 RSI: 00007fff552c1160 RDI: 000000000000000a
RBP: 0000000000000000
R8: 0000000000000000
R9: 0000000000000200
R10: 00007fff552c1060 R11: 0000000000000246 R12: 00007fff552c1160
R13: 00007fff552c10e0 R14: 00007fff552c1060 R15: 00007fff552c121f
ORIG_RAX: 0000000000000017 CS: 0033 SS: 002b
bt is probably the most useful crash command. It has a large number of options that you can
use to examine a kernel stack trace. For more information, enter help bt.
102
System State Commands
dev
Displays character and block device data. The -d and -i options display disk I/O statistics and I/
O port usage. For example:
crash> dev
CHRDEV
NAME
CDEV
OPERATIONS
1
mem
ffff88007d2a66c0 memory_fops
4
/dev/vc/0
ffffffff821f6e30 console_fops
4
tty
ffff88007a395008 tty_fops
4
ttyS
ffff88007a3d3808 tty_fops
5
/dev/tty
ffffffff821f48c0 tty_fops
...
BLKDEV
NAME
GENDISK
OPERATIONS
1
ramdisk
ffff88007a3de800 brd_fops
259
blkext
(none)
7
loop
ffff880037809800 lo_fops
8
sd
ffff8800378e9800 sd_fops
9
md
(none)
...
crash> dev -d
MAJOR GENDISK
NAME
REQUEST QUEUE
TOTAL ASYNC
8 0xffff8800378e9800 sda
0xffff880037b513e0
10
0
11 0xffff880037cde400 sr0
0xffff880037b50b10
0
0
253 0xffff880037902c00 dm-0
0xffff88003705b420
0
0
253 0xffff880037d5f000 dm-1
0xffff88003705ab50
0
0
crash> dev -i
RESOURCE
RANGE
NAME
ffffffff81a9e1e0 0000-ffff PCI IO
ffffffff81a96e30 0000-001f dma1
ffffffff81a96e68 0020-0021 pic1
ffffffff81a96ea0 0040-0043 timer0
ffffffff81a96ed8 0050-0053 timer1
ffffffff81a96f10 0060-0060 keyboard
...
files
SYNC
10
0
0
0
DRV
0
0
0
0
Displays information about files that are open in the current context or in the context of a specific
PID or task. For example:
crash> files 12916
PID: 12916 TASK: ffff8800276a2480 CPU: 0
COMMAND: "firefox"
ROOT: /
CWD: /home/guest
FD
FILE
DENTRY
INODE
TYPE PATH
0 ffff88001c57ab00 ffff88007ac399c0 ffff8800378b1b68 CHR /null
1 ffff88007b315cc0 ffff88006046f800 ffff8800604464f0 REG /home/guest/.xsession-errors
2 ffff88007b315cc0 ffff88006046f800 ffff8800604464f0 REG /home/guest/.xsession-errors
3 ffff88001c571a40 ffff88001d605980 ffff88001be45cd0 REG /home/guest/.mozilla/firefox
4 ffff88003faa7300 ffff880063d83440 ffff88001c315bc8 SOCK
5 ffff88003f8f6a40 ffff88007b41f080 ffff88007aef0a48 FIFO
...
fuser
Displays the tasks that reference a specified file name or inode address as the current root
directory, current working directory, open file descriptor, or that memory map the file. For
example:
crash>
PID
2990
3116
3142
3147
3162
3185
...
irq
fuser /home/guest
TASK
ffff88007a2a8440
ffff8800372e6380
ffff88007c54e540
ffff88007aa1e440
ffff88007a2d04c0
ffff88007c00a140
COMM
"gnome-session"
"gnome-session"
"metacity"
"gnome-panel"
"nautilus"
"bluetooth-appl
USAGE
cwd
cwd
cwd
cwd
cwd
cwd
Displays interrupt request queue data. For example:
103
System State Commands
crash> irq 0
IRQ: 0
STATUS: 400000 ()
HANDLER: ffffffff81b3da30
typename: ffffffff815cdaef
startup: ffffffff8102a513
shutdown: ffffffff810aef92
enable: ffffffff810aefe3
disable: ffffffff810aeecc
ack: ffffffff8102a43d
mask: ffffffff81029be1
...
kmem
<ioapic_chip>
"IO-APIC"
<startup_ioapic_irq>
<default_shutdown>
<default_enable>
<default_disable>
<ack_apic_edge>
<mask_IO_APIC_irq>
Displays the state of the kernel memory subsystems. For example:
crash> kmem -i
TOTAL MEM
FREE
USED
SHARED
BUFFERS
CACHED
SLAB
PAGES
512658
20867
491791
176201
8375
229933
39551
TOTAL
2 GB
81.5 MB
1.9 GB
688.3 MB
32.7 MB
898.2 MB
154.5 MB
TOTAL SWAP
SWAP USED
SWAP FREE
1032190
2067
1030123
3.9 GB
8.1 MB
3.9 GB
PERCENTAGE
---4% of TOTAL MEM
95% of TOTAL MEM
34% of TOTAL MEM
1% of TOTAL MEM
44% of TOTAL MEM
7% of TOTAL MEM
---0% of TOTAL SWAP
99% of TOTAL SWAP
kmem has a large number of options. For more information, enter help kmem.
log
Displays the kernel message buffer in chronological order. This is the same data that dmesg
displays but the output can include messages that never made it to syslog or disk.
mach
Displays machine-specific information such as the cpuinfo structure and the physical memory
map.
mod
Displays information about the currently installed kernel modules. The -s and -S options load
debug data (if available) from the specified module object files to enable symbolic debugging.
mount
Displays information about currently mounted file systems.
net
Displays network-related information.
ps
Displays information about processes. For example:
crash> ps Xorg crash bash
PID
PPID CPU
TASK
2679
2677
0 ffff88007cbcc400
> 13362 11853
0 ffff88007b25a500
3685
3683
1 ffff880058714580
11853 11845
1 ffff88001c6826c0
ST
IN
RU
IN
IN
%MEM
4.0
6.9
0.1
0.1
VSZ
RSS
215488 84880
277632 145612
108464
1984
108464
1896
COMM
Xorg
crash
bash
bash
pte
Translates a page table entry (PTE) to the physical page address and page bit settings. If the PTE
refers to a swap location, the command displays the swap device and offset.
runq
Displays the list of tasks that are on the run queue of each CPU.
sig
Displays signal-handling information for the current context or for a specified PID or task.
swap
Displays information about the configured swap devices.
task
Displays the contents of the task_struct for the current context or for a specified PID or task.
104
Helper Commands
timer
Displays the entries in the timer queue in chronological order.
vm
Displays the virtual memory data, including the addresses of mm_struct and the page directory,
resident set size, and total virtual memory size for the current context or for a specified PID or
task.
vtop
Translates a user or kernel virtual address to a physical address. The command also displays the
PTE translation, vm_area_struct data for user virtual addresses, mem_map page data for a
physical page, and the swap location or file location if the page is not mapped.
waitq
Displays tasks that are blocked on a specified wait queue.
10.2.5 Helper Commands
The following commands perform calculation, translation, and search functions:
ascii
Translates a hexadecimal value to ASCII. With no argument, the command displays an ASCII
chart.
btop
Translates a hexadecimal address to a page number.
eval
Evaluates an expression and displays the result in hexadecimal, decimal, octal, and binary. For
example:
crash> eval 4g / 0x100
hexadecimal: 1000000 (16MB)
decimal: 16777216
octal: 100000000
binary: 0000000000000000000000000000000000000001000000000000000000000000
list
Displays the contents of a linked list of data objects, typically structures, starting at a specified
address.
ptob
Translates a page number to its physical address (byte value).
ptov
Translates a physical address to a kernel virtual address.
search
Searches for a specified value in a specified range of user virtual memory, kernel virtual
memory, or physical memory.
rd
Displays a selected range of user virtual memory, kernel virtual memory, or physical memory
using the specified format.
wr
Writes a value to a memory location specified by symbol or address.
Warning
To avoid data loss or data corruption, take great care when using the wr
command.
10.2.6 Session Control Commands
The following commands control the crash session:
alias
Defines an alias for a command. With no argument, the command displays the
current list of aliases.
exit, q, or quit
Ends the crash session.
105
Guidelines for Examining a Dump File
extend
Loads or unloads the specified crash extension shared object libraries.
foreach
Execute a bt, files, net, task, set, sig, vm, or vtop command on multiple
tasks.
gdb
Passes any arguments to the GNU Debugger for processing.
repeat
Repeats a command indefinitely until you type Ctrl-C. This command is only
useful when you use crash to examine a live system.
set
Sets the context to a specified PID or task. With no argument, the command
displays the current context.
10.2.7 Guidelines for Examining a Dump File
The steps for debugging a memory dump from a kernel crash vary widely according to the problem. The
following guidelines suggest some basic investigations that you can try:
• Use bt to trace the functions that led to the kernel panic.
• Use bt -a to trace the active task on each CPU. There is often a relationship between the panicking
task on one CPU and the running tasks on the other CPUs. If the listed command is cpu_idle or
swapper, no task was running on a CPU.
• Use bt –l to display the line number of the source files corresponding to each function call in the stack
trace.
• Use kmem –i to obtain a summary of memory and swap usage. Look for a SLAB value greater than 500
MB and a SWAP USED value greater than 0%.
• Use ps | grep UN to check for processes in the TASK_UNINTERRUPTIBLE state (D state), usually
because they are waiting on I/O. Such processes contribute to the load average and cannot be killed.
• Use files to display the files that a process had open.
You can shell indirection operators to save output from a command to a file for later analysis or to pipe the
output through commands such as grep, for example:
crash> foreach files > files.txt
crash> foreach bt | grep bash
PID: 3685
TASK: ffff880058714580
PID: 11853 TASK: ffff88001c6826c0
CPU: 1
CPU: 0
COMMAND: "bash"
COMMAND: "bash"
106
Part II Networking and Network Services
This section contains the following chapters:
• Chapter 11, Network Configuration describes how to configure a system's network interfaces and network routing.
• Chapter 12, Network Address Configuration describes how to configure a DHCP server, DHCP client, and Network
Address Translation.
• Chapter 13, Name Service Configuration describes how to use BIND to set up a DNS name server.
• Chapter 14, Network Time Configuration describes how to configure the Network Time Protocol (NTP) or Precision
Time Protocol (PTP) daemons for setting the system time.
• Chapter 15, Web Service Configuration describes how to configure a basic HTTP server.
• Chapter 16, Email Service Configuration describes email programs and protocols that are available with Oracle
Linux, and how to set up a basic Sendmail client.
Table of Contents
11 Network Configuration ................................................................................................................ 111
11.1 About Network Interfaces ................................................................................................ 111
11.2 About Network Configuration Files ................................................................................... 113
11.2.1 /etc/hosts .............................................................................................................. 113
11.2.2 /etc/nsswitch.conf .................................................................................................. 113
11.2.3 /etc/resolv.conf ..................................................................................................... 113
11.2.4 /etc/sysconfig/network ........................................................................................... 114
11.3 Command-line Network Configuration Interfaces ............................................................... 114
11.4 Configuring Network Interfaces Using Graphical Interfaces ................................................ 116
11.5 Configuring Network Interface Bonding ............................................................................ 117
11.5.1 Using ifenslave to Create Bonded Interfaces .......................................................... 118
11.6 Configuring VLANs with Untagged Data Frames ............................................................... 119
11.6.1 Using vconfig to Create VLAN Devices .................................................................. 120
11.7 Configuring Network Routing ........................................................................................... 120
12 Network Address Configuration .................................................................................................. 123
12.1 About the Dynamic Host Configuration Protocol ................................................................ 123
12.2 Configuring a DHCP Server ............................................................................................. 123
12.3 Configuring a DHCP Client .............................................................................................. 124
12.4 About Network Address Translation ................................................................................. 125
13 Name Service Configuration ....................................................................................................... 127
13.1 About DNS and BIND ..................................................................................................... 127
13.2 About Types of Name Servers ......................................................................................... 128
13.3 About DNS Configuration Files ........................................................................................ 128
13.3.1 /etc/named.conf .................................................................................................... 128
13.3.2 About Resource Records in Zone Files ................................................................. 131
13.3.3 About Resource Records for Reverse-name Resolution .......................................... 132
13.4 Configuring a Name Server ............................................................................................. 133
13.5 Administering the Name Service ...................................................................................... 134
13.6 Performing DNS Lookups ................................................................................................ 135
14 Network Time Configuration ....................................................................................................... 137
14.1 About the NTP Daemon .................................................................................................. 137
14.1.1 Configuring the ntpd Service ................................................................................. 137
14.2 About PTP ...................................................................................................................... 138
14.2.1 Configuring the PTP Service ................................................................................. 139
14.2.2 Using PTP as a Time Source for NTP ................................................................... 141
15 Web Service Configuration ......................................................................................................... 143
15.1 About the Apache HTTP Server ...................................................................................... 143
15.2 Installing the Apache HTTP Server .................................................................................. 143
15.3 Configuring the Apache HTTP Server .............................................................................. 143
15.4 Testing the Apache HTTP Server .................................................................................... 146
15.5 Configuring Apache Containers ........................................................................................ 146
15.5.1 About Nested Containers ...................................................................................... 147
15.6 Configuring Apache Virtual Hosts .................................................................................... 148
16 Email Service Configuration ....................................................................................................... 149
16.1 About Email Programs .................................................................................................... 149
16.2 About Email Protocols ..................................................................................................... 149
16.2.1 About SMTP ........................................................................................................ 149
16.2.2 About POP and IMAP .......................................................................................... 150
16.3 About the Postfix SMTP Server ....................................................................................... 150
16.4 About the Sendmail SMTP Server ................................................................................... 151
16.4.1 About Sendmail Configuration Files ....................................................................... 151
109
16.5 Forwarding Email ............................................................................................................ 152
16.6 Configuring a Sendmail Client ......................................................................................... 152
110
Chapter 11 Network Configuration
Table of Contents
11.1 About Network Interfaces ........................................................................................................ 111
11.2 About Network Configuration Files ........................................................................................... 113
11.2.1 /etc/hosts ...................................................................................................................... 113
11.2.2 /etc/nsswitch.conf .......................................................................................................... 113
11.2.3 /etc/resolv.conf ............................................................................................................. 113
11.2.4 /etc/sysconfig/network ................................................................................................... 114
11.3 Command-line Network Configuration Interfaces ....................................................................... 114
11.4 Configuring Network Interfaces Using Graphical Interfaces ........................................................ 116
11.5 Configuring Network Interface Bonding .................................................................................... 117
11.5.1 Using ifenslave to Create Bonded Interfaces ................................................................. 118
11.6 Configuring VLANs with Untagged Data Frames ....................................................................... 119
11.6.1 Using vconfig to Create VLAN Devices ......................................................................... 120
11.7 Configuring Network Routing ................................................................................................... 120
This chapter describes how to configure a system's network interfaces and network routing.
11.1 About Network Interfaces
Each physical and virtual network device on an Oracle Linux system has an associated configuration file
named ifcfg-interface in the /etc/sysconfig/network-scripts directory, where interface
is the name of the interface. For example:
# cd /etc/sysconfig/network-scripts
# ls ifcfg-*
ifcfg-eth0 ifcfg-eth1 ifcfg-lo
In this example, there are two configuration files for Ethernet interfaces, ifcfg-eth0 and ifcfg-eth1,
and one for the loopback interface, ifcfg-lo. The system reads the configuration files at boot time to
configure the network interfaces.
The following are sample entries from an ifcfg-eth0 file for a network interface that obtains its IP
address using the Dynamic Host Configuration Protocol (DHCP):
DEVICE="eth0"
NM_CONTROLLED="yes"
ONBOOT=yes
USERCTL=no
TYPE=Ethernet
BOOTPROTO=dhcp
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
HWADDR=08:00:27:16:C3:33
PEERDNS=yes
PEERROUTES=yes
If the interface is configured with a static IP address, the file contains entries such as the following:
DEVICE="eth0"
NM_CONTROLLED="yes"
111
About Network Interfaces
ONBOOT=yes
USERCTL=no
TYPE=Ethernet
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"
UUID=5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03
HWADDR=08:00:27:16:C3:33
IPADDR=192.168.1.101
NETMASK=255.255.255.0
BROADCAST=192.168.1.255
PEERDNS=yes
PEERROUTES=yes
The following configuration parameters are typically used in interface configuration files:
BOOTPROTO
How the interface obtains its IP address:
bootp
Bootstrap Protocol (BOOTP).
dhcp
Dynamic Host Configuration Protocol (DHCP).
none
Statically configured IP address.
BROADCAST
IPv4 broadcast address.
DEFROUTE
Whether this interface is the default route.
DEVICE
Name of the physical network interface device (or a PPP logical device).
HWADDR
Media access control (MAC) address of an Ethernet device.
IPADDR
IPv4 address of the interface.
IPV4_FAILURE_FATAL
Whether the device is disabled if IPv4 configuration fails.
IPV6_FAILURE_FATAL
Whether the device is disabled if IPv6 configuration fails.
IPV6ADDR
IPv6 address of the interface in CIDR notation. For example:
IPV6ADDR="2001:db8:1e11:115b::1/32"
IPV6INIT
Whether to enable IPv6 for the interface.
MASTER
Specifies the name of the master bonded interface, of which this interface is
slave.
NAME
Name of the interface as displayed in the Network Connections GUI.
NETMASK
IPv4 network mask of the interface.
NETWORK
IPV4 address of the network.
NM_CONTROLLED
Whether the network interface device is controlled by the network management
daemon, NetworkManager.
ONBOOT
Whether the interface is activated at boot time.
PEERDNS
Whether the /etc/resolv.conf file used for DNS resolution contains
information obtained from the DHCP server.
112
About Network Configuration Files
PEERROUTES
Whether the information for the routing table entry that defines the default
gateway for the interface is obtained from the DHCP server.
SLAVE
Specifies that this interface is a component of a bonded interface.
TYPE
Interface type.
USERCTL
Whether users other than root can control the state of this interface.
UUID
Universally unique identifier for the network interface device.
11.2 About Network Configuration Files
The following sections describe additional network configuration files that you might need to configure on a
system.
11.2.1 /etc/hosts
The /etc/hosts file associates host names with IP addresses. It allows the system to look up (resolve)
the IP address of a host given its name, or the name given the UP address. Most networks use DNS
(Domain Name Service) to perform address or name resolution. Even if your network uses DNS, it is usual
to include lines in this file that specify the IPv4 and IPv6 addresses of the loopback device, for example:
127.0.0.1
::1
localhost localhost.localdomain localhost4 localhost4.localdomain4
localhost localhost.localdomain localhost6 localhost6.localdomain6
The first and second column contains the IP address and host name. Additional columns contain aliases
for the host name.
For more information, see the hosts(5) manual page.
11.2.2 /etc/nsswitch.conf
The /etc/nsswitch.conf file configures how the system uses various databases and name resolution
mechanisms. The first field of entries in this file identifies the name of the database. The second field
defines a list of resolution mechanisms in the order in which the system attempts to resolve queries on the
database.
The following example hosts definition from /etc/nsswitch.conf indicates that the system first
attempts to resolve host names and IP addresses by querying files (that is, /etc/hosts) and, if that
fails, next by querying a DNS server, and last of all, by querying NIS+ (NIS version 3) :
hosts:
files dns nisplus
For more information, see the nsswitch.conf(5) manual page.
11.2.3 /etc/resolv.conf
The /etc/resolv.conf file defines how the system uses DNS to resolve host names and IP addresses.
This file usually contains a line specifying the search domains and up to three lines that specify the IP
addresses of DNS server. The following entries from /etc/resolv.conf configure two search domains
and three DNS servers:
search us.mydomain.com mydomain.com
nameserver 192.168.154.3
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/etc/sysconfig/network
nameserver 192.168.154.4
nameserver 10.216.106.3
If your system obtains its IP address from a DHCP server, it is usual for the system to configure the
contents of this file with information also obtained using DHCP.
For more information, see the resolv.conf(5) manual page.
11.2.4 /etc/sysconfig/network
The /etc/sysconfig/network file specifies additional information that is valid to all network interfaces
on the system. The following entries from /etc/sysconfig/network define that IPv4 networking is
enabled, IPv6 networking is not enabled, the host name of the system, and the IP address of the default
network gateway:
NETWORKING=yes
NETWORKING_IPV6=no
HOSTNAME=host20.mydomain.com
GATEWAY=192.168.1.1
For more information, see /usr/share/doc/initscripts*/sysconfig.txt.
11.3 Command-line Network Configuration Interfaces
If the NetworkManager service is running, you can use the nm-tool command to display a verbose
listing of the state of the system's physical network interfaces, for example:
# nm-tool
NetworkManager Tool
State: connected
- Device: eth0
Type:
Driver:
State:
Default:
HW Address:
[System eth0] -------------------------------------------------Wired
e1000
connected
yes
08:00:27:16:C3:33
Capabilities:
Carrier Detect:
Speed:
yes
1000 Mb/s
Wired Properties
Carrier:
on
IPv4 Settings:
Address:
Prefix:
Gateway:
10.0.2.15
24 (255.255.255.0)
10.0.2.2
DNS:
DNS:
192.168.249.52
192.168.249.41
You can also use the ip command to display the status of an interface, for debugging, or for system
tuning. For example, to display the status of all active interfaces:
# ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
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Command-line Network Configuration Interfaces
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 08:00:27:16:c3:33 brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global eth0
inet6 fe80::a00:27ff:fe16:c333/64 scope link
valid_lft forever preferred_lft forever
For each network interface, the output shows the current IP address, and the status of the interface. To
display the status of a single interface such as eth0, specify its name as shown here:
# ip addr show dev eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 08:00:27:16:c3:33 brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global eth0
inet6 fe80::a00:27ff:fe16:c333/64 scope link
valid_lft forever preferred_lft forever
You can also use ip to set properties and activate a network interface. The following example sets the IP
address of the eth1 interface and activates it:
# ip addr add 10.1.1.1/24 dev eth1
# ip link set eth1 up
Note
You might be used to using the ifconfig command to perform these operations.
However, ifconfig is considered obsolete and will eventually be replaced
altogether by the ip command.
Any settings that you configure for network interfaces using ip do not persist across system reboots.
To make the changes permanent, set the properties in the /etc/sysconfig/network-scripts/
ifcfg-interface file.
Any changes that you make to an interface file in /etc/sysconfig/network-scripts do not take
effect until you restart the network service or bring the interface down and back up again. For example, to
restart the network service:
# service network restart
Shutting down interface eth0:
Device state: 3 (disconnected)
[ OK ]
Shutting down loopback interface:
[ OK ]
Bringing up loopback interface:
[ OK ]
Bringing up interface eth0: Active connection state: activating
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/1
state: activated
Connection activated
[ OK ]
To restart an individual interface, you can use the ifup or ifdown commands, which invoke the script in /
etc/sysconfig/network-scripts that corresponds to the interface type, for example:
# ifdown eth0
Device state: 3 (disconnected)
# ifup eth0
Active connection state: activating
Active connection path: /org/freedesktop/NetworkManager/ActiveConnection/1
state: activated
Connection activated
Alternatively, you can use the ip command:
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Configuring Network Interfaces Using Graphical Interfaces
# ip link set eth0 down
# ip link set eth0 up
The ethtool utility is useful for diagnosing potentially mismatched settings that affect performance, and
allows you to query and set the low-level properties of a network device. Any changes that you make using
ethtool do not persist across a reboot. To make the changes permanent, modify the settings in the
device's ifcfg-interface file in /etc/sysconfig/network-scripts.
For more information, see the ethtool(8), ifup(8), ip(8), and nm-tool(1) manual pages.
11.4 Configuring Network Interfaces Using Graphical Interfaces
Note
The NetworkManager service, Gnome graphical applet, and the nmconnection-editor command are included in the NetworkManager package.
The system-config-network utility is included in the system-confignetwork-tui package.
The NetworkManager service dynamically detects and configures network connections. It includes a
GNOME Notification Area applet (nm-applet)that provides you with information about the network status
and graphical configuration tools to manage network interfaces and connections.
The applet icon changes its appearance indicate the state of the network. Hover the mouse pointer over
the icon to display more information as a tool tip. Clicking the icon displays a drop-down menu that allows
you to restart or disconnect each named interface.
Right-clicking the icon displays a different drop-down menu:
Enable Networking
Allows you to stop or start the network service.
Enable Notifications
Controls whether NetworkManager notifies you of changes to the status
of network connections.
Connection Information
Displays the Connection Information window, which lists the connection
type, hardware address, IP address, and other useful information for each
interface.
Edit Connections
Displays the Network Connections window, which allows you to configure
wired, wireless, mobile broadband, Virtual Private Network (VPN), and
Digital Subscriber Link (DSL) interfaces. You can also open this window by
using the nm-connection-editor command.
Figure 11.1 shows the Network Connections window with the Wired tab selected.
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Configuring Network Interface Bonding
Figure 11.1 Network Connections Window
You can also use the system-config-network command, which provides a text-based user interface
that allows you to configure network interface and DNS resolver settings.
11.5 Configuring Network Interface Bonding
Network interface bonding (also known as port trunking, channel bonding, link aggregation, NIC teaming,
among other names) combines multiple network connections into a single logical interface. A bonded
network interface can increase data throughput by load balancing or can provide redundancy by allowing
failover from one component device to another. By default, a bonded interface appears like a normal
network device to the kernel, but it sends out network packets over the available slave devices by using
a simple round-robin scheduler. You can configure bonding module parameters in the bonded interface's
configuration file to alter the behavior of load-balancing and device failover.
Basic load-balancing modes (balance-rr and balance-xor) work with any switch that supports
EtherChannel or trunking. Advanced load-balancing modes (balance-tlb and balance-alb) do not
impose requirements on the switching hardware, but do require that the device driver for each component
interfaces implement certain specific features such as support for ethtool or the ability to modify the
hardware address while the device is active. For more information see /usr/share/doc/iputils-*/
README.bonding.
You can use the bonding driver that is provided with the Oracle Linux kernel to aggregate multiple network
interfaces, such as eth0 and eth1, into a single logical interface such as bond0.
To create a bonded interface:
1. Create a file named ifcfg-bondN in the /etc/sysconfig/network-scripts directory, where N
is number of the interface, such as 0.
2. Edit the contents of ifcfg-bondN to be similar to the configuration settings for an Ethernet interface
except that DEVICE is set to bondN rather than ethn, for example:
DEVICE="bond0"
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Using ifenslave to Create Bonded Interfaces
IPADDR=192.168.1.121
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
TYPE=Ethernet
BONDING_OPTS="bonding parameters separated by spaces"
The BONDING_OPTS setting is optional, unless you need to pass parameters to the bonding module,
for example, to specify the load balancing mechanism or to configure ARP link monitoring. For more
information, see /usr/share/doc/iputils-*/README.bonding.
3. For each interface that you want to bond, edit its ifcfg-interface file so that it contains
MASTER=bondN and SLAVE entries, for example:
DEVICE="eth0"
NAME="System eth0"
IPADDR=192.168.1.101
NETMASK=255.255.255.0
BROADCAST=192.0.2.255
NM_CONTROLLED="yes"
ONBOOT=yes
USERCTL=no
TYPE=Ethernet
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
PEERDNS=yes
PEERROUTES=yes
MASTER=bond0
SLAVE
4. Create the file /etc/modprobe.d/bonding.conf, so that it contains an entry for each bonded
interface, for example:
alias bond0 bonding
The existence of this file ensures that the kernel loads the bonding module is loaded when you bring up
the bonded interface. All bonded interfaces that you configure require an entry in this file.
5. If the component interfaces are up, bring them down, and then bring up the bonded interface:
# ip link set eth0 down
# ip link set eth1 down
# ip link set bond0 up
11.5.1 Using ifenslave to Create Bonded Interfaces
The ifenslave command provides an alternate method of creating bonded interfaces. Only round-robin
load balancing is available.
To create a bonded device by using the ifenslave command:
1. Load the bonding module:
# modprobe bonding
2. Configure the network settings for the bonded interface:
# ip addr add 192.168.1.121/24 dev bond0
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Configuring VLANs with Untagged Data Frames
3. Attach the component network interfaces to the bonded interface:
# ifenslave bond0 eth0 eth1
4. Bring up the bonded interface:
# ip link set bond0 up
For more information, see the ifenslave(8) manual page.
11.6 Configuring VLANs with Untagged Data Frames
A virtual local area network (VLAN) consists of a group of machines that can communicate as if they were
attached to the same physical network. A VLAN allows you to group systems regardless of their actual
physical location on a LAN. In a VLAN that uses untagged data frames, you create the broadcast domain
by assigning the ports of network switches to the same permanent VLAN ID or PVID (other than 1, which
is the default VLAN). All ports that you assign with this PVID are in a single broadcast domain. Broadcasts
between devices in the same VLAN are not visible to other ports with a different VLAN, even if they exist
on the same switch.
To create a VLAN device for a network interface or bonded interface:
1. Create a file named ifcfg-interface.pvid in the /etc/sysconfig/network-scripts
directory, by copying the ifcfg-interface configuration file for the interface that is connected to a
port that implements the PVID that is identified by pvid.
For example, if the PVID of the switch port is 5 and the interface connected to it is eth0, copy the
ifcfg-eth0 file to ifcfg-eth0.5:
# cd /etc/sysconfig/network-scripts
# cp ifcfg-eth0 ifcfg-eth0.5
For the bonded interface bond0, where the PVID of the connected switch ports is 10, copy the ifcfgbond0 file to ifcfg-bond0.10:
# cd /etc/sysconfig/network-scripts
# cp ifcfg-bond0 ifcfg-bond0.10
Note
You do not need to create virtual interfaces for the component interfaces of the
bonded interface. However, you must set the PVID on each switch port to which
they connect.
2. Edit the ifcfg-interface.pvid file, change the DEVICE (and NAME, if specified) entries, and add a
VLAN=yes entry. For example, ifcfg-eth0.5 would appear similar to the following:
DEVICE="eth0.5"
NAME="System eth0.5"
VLAN=yes
IPADDR=192.168.1.101
NETMASK=255.255.255.0
BROADCAST=192.0.2.255
NM_CONTROLLED="yes"
ONBOOT=yes
USERCTL=no
TYPE=Ethernet
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
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Using vconfig to Create VLAN Devices
IPV6INIT=no
PEERDNS=yes
PEERROUTES=yes
and ifcfg-bond0.10 as:
DEVICE="bond0.10"
VLAN=yes
IPADDR=192.168.1.121
NETMASK=255.255.255.0
NETWORK=192.168.1.0
BROADCAST=192.168.1.255
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
TYPE=Ethernet
Save your changes to the file. Do not edit the original ifcfg-ethN file.
3. Restart the network:
# service network restart
In addition to the regular interface, eth0 or bond0, which uses the physical LAN, you now have a
VLAN device, such as eth0.5 or bond0.10, which can use untagged frames to access the virtual
LAN.
To obtain detailed information about VLAN interfaces, view the /proc/net/vlan directory.
11.6.1 Using vconfig to Create VLAN Devices
The vconfig command provides an alternate method of creating VLAN devices.
To create a VLAN device by using the vconfig command:
1. Add a VLAN interface definition, eth0.5, for eth0 on PVID 5:
# vconfig add eth0 5
2. Configure the network settings for the VLAN interface:
# ip addr add 192.168.1.121/24 dev eth0.5
3. Bring up the VLAN interface:
# ip link set eth0.5 up
If you subsequently need to delete the interface, use the following commands to bring it down and
remove its definition:
# ip link set eth0.5 down
# vconfig rem eth0.5
For more information, see the vconfig(8) manual page.
11.7 Configuring Network Routing
A system uses its routing table to determine which network interface to use when sending packets to
remote systems. If a system has only a single interface, it is sufficient to configure the IP address of a
gateway system on the local network that routes packets to other networks.
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Configuring Network Routing
To create a default route for IPv4 network packets, include an entry for GATEWAY in the /etc/
sysconfig/network file. For example, the following entry configures the IP address of the gateway
system:
GATEWAY=192.0.2.1
If your system has more than one network interface, you can specify which interface should be used:
GATEWAY=192.0.2.1
GATEWAYDEV=eth0
A single statement is usually sufficient to define the gateway for IPv6 packets, for example:
IPV6_DEFAULTGW="2001:db8:1e10:115b::2%eth0"
Any changes that you make to /etc/sysconfig/network do not take effect until you restart the
network service:
# service network restart
To display the routing table, use the ip route show command, for example:
# ip route show
10.0.2.0/24 dev eth0 proto kernel scope link
default via 10.0.2.2 dev eth0 proto static
src 10.0.2.15
This example shows that packets destined for the local network (10.0.2.0/24) do not use the gateway. The
default entry means that any packets destined for addresses outside the local network are routed via the
gateway 10.0.2.2.
Note
You might be used to using the route command to configure routing. However,
route is considered obsolete and will eventually be replaced altogether by the ip
command.
You can also use the netstat -rn command to display this information:
Kernel IP routing table
Destination
Gateway
10.0.2.0
0.0.0.0
0.0.0.0
10.0.2.2
Genmask
255.255.255.0
0.0.0.0
Flags
U
UG
MSS Window
0 0
0 0
irtt Iface
0 eth0
0 eth0
To add or delete a route from the table, use the ip route add or ip route del commands. For
example, to replace the entry for the static default route:
# ip route del default
# ip route show
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15
# ip ro add default via 10.0.2.1 dev eth0 proto static
# ip route show
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15
default via 10.0.2.1 dev eth0 proto static
To add a route to the network 10.0.3.0/24 via 10.0.3.1 over interface eth1, and then delete that route:
# ip route add 10.0.4.0/24 via 10.0.2.1 dev eth1
# ip route show
10.0.2.0/24 dev eth0 proto kernel scope link src 10.0.2.15
10.0.3.0/24 via 10.0.3.1 dev eth1
default via 10.0.2.2 dev eth0 proto static
# ip route del 10.0.3.0/24
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Configuring Network Routing
# ip route show
10.0.2.0/24 dev eth0 proto kernel scope link
default via 10.0.2.2 dev eth0 proto static
src 10.0.2.15
The ip route get command is a useful feature that allows you to query the route on which the system
will send packets to reach a specified IP address, for example:
# ip route get 23.6.118.140
23.6.118.140 via 10.0.2.2 dev eth0 src 10.0.2.15
cache mtu 1500 advmss 1460 hoplimit 64
In this example, packets to 23.6.118.140 are sent out of the eth0 interface via the gateway 10.0.2.2.
Any changes that you make to the routing table using ip route do not persist across system reboots.
To permanently configure static routes, you can configure them by creating a route-interface file in/
etc/sysconfig/network-scripts for the interface. For example, you would configure a static route
for the eth0 interface in a file named route-eth0. An entry in these files can take the same format as the
arguments to the ip route add command.
For example, to define a default gateway entry for eth0, create an entry such as the following in routeeth0:
default via 10.0.2.1 dev eth0
The following entry in route-eth1 would define a route to 10.0.3.0/24 via 10.0.3.1 over eth1:
10.0.3.0/24 via 10.0.3.1 dev eth1
Any changes that you make to a route-interface file do not take effect until you restart either the
network service or the interface.
For more information, see the ip(8) and netstat(8) manual pages.
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Chapter 12 Network Address Configuration
Table of Contents
12.1
12.2
12.3
12.4
About the Dynamic Host Configuration Protocol ........................................................................
Configuring a DHCP Server .....................................................................................................
Configuring a DHCP Client ......................................................................................................
About Network Address Translation .........................................................................................
123
123
124
125
This chapter describes how to configure a DHCP server, DHCP client, and Network Address Translation.
12.1 About the Dynamic Host Configuration Protocol
The Dynamic Host Configuration Protocol (DHCP) allows client systems to obtain network configuration
information from a DHCP server each time that they connect to the network. The DHCP server is
configured with a range of IP addresses and other network configuration parameters that clients need.
When you configure an Oracle Linux system as a DHCP client, the client daemon, dhclient, contacts the
DHCP server to obtain the networking parameters. As DHCP is broadcast-based, the client must be on the
same subnet as either a server or a relay agent. If a client cannot be on the same subnet as the server, a
DHCP relay agent can be used to pass DHCP messages between subnets.
The server provides a lease for the IP address that it assigns to a client. The client can request specific
terms for the lease, such as the duration. You can configure a DHCP server to limit the terms that it can
grant for a lease. Provided that a client remains connected to the network, dhclient automatically renews
the lease before it expires. You can configure the DHCP server to provide the same IP address to a client
based on the MAC address of its network interface.
The advantages of using DHCP include:
• centralized management of IP addresses
• ease of adding new clients to a network
• reuse of IP addresses reducing the total number of IP addresses that are required
• simple reconfiguration of the IP address space on the DHCP server without needing to reconfigure each
client
For more information about DHCP, see RFC 2131.
12.2 Configuring a DHCP Server
To configure an Oracle Linux system as a DHCP server:
1. Install the dhcp package:
#
yum install dhcp
2. Edit the /etc/dhcp/dhcpd.conf file to store the settings that the DHCP server can provide to the
clients.
The following example configures the domain name, a range of client addresses on the 192.168.2.0/24
subnet from 192.168.2.101 through 192.168.2.254 together with the IP addresses of the default
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Configuring a DHCP Client
gateway and the DNS server, the default and maximum lease times in seconds, and a static IP address
for the application server svr01 that is identified by its MAC address:
option
option
option
option
domain-name "mydom.org";
domain-name-servers 192.168.2.1, 10.0.1.4;
broadcast-address 192.168.2.255;
routers 192.168.2.1;
subnet 192.168.2.0 netmask 255.255.255.0 {
range 192.168.2.101 192.168.2.254;
default-lease-time 10800;
max-lease-time 43200;
}
host svr01 {
hardware ethernet 80:56:3e:00:10:00;
fixed-address 192.168.2.100;
max-lease-time 86400;
}
The DHCP server sends the information in the option lines to each client when it requests a lease
on an IP address. An option applies only to a subnet if you define it inside a subnet definition. In the
example, the options are global and apply to both the subnet and host definitions. The subnet and
host definitions have different settings for the maximum lease time.
For more information and examples, see /usr/share/doc/dhcp-version/dhcpd.conf.sample
and the dhcp-options(5) manual page.
3. Edit /etc/sysconfig/dhcpd to configure settings for the DHCP server itself. For example, the
following setting specifies the interfaces on which the server listens for DHCP requests:
DHCPDARGS="eth0 eth1"
For more information, see the dhcpd(8) manual page.
4. Touch the /var/lib/dhcpd/dhcpd.leases file, which stores information about client leases:
# touch /var/lib/dhcpd/dhcpd.leases
5. Enter the following commands to start the DHCP service and ensure that it starts after a reboot:
# service dhcpd start
# chkconfig dhcpd on
For information about configuring a DHCP relay, see the dhcrelay(8) manual page.
12.3 Configuring a DHCP Client
To configure an Oracle Linux system as a DHCP client:
1. Install the dhclient package:
# yum install dhclient
2. Edit /container/name/rootfs/etc/sysconfig/network-scripts/ifcfg-iface, where
iface is the name of the network interface, and change the value of BOOTPROTO to read as:
BOOTPROTO=dhcp
3. Edit /etc/sysconfig/network and verify that it contains the following setting:
NETWORKING=yes
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About Network Address Translation
4. To specify options for the client, such as the requested lease time and the network interface on which
to request an address from the server, create the file /etc/dhclient.conf containing the required
options.
The following example specifies that the client should use the eth1 interface, request a lease time of
24 hours, and identify itself using its MAC address:
interface "eth1" {
send dhcp-lease-time 86400;
send dhcp-client-identifier 80:56:3e:00:10:00;
}
For more information, see the dhclient.conf(5) manual page.
5. Restart the network interface or the network service to enable the client, for example:
# service network restart
When the client has requested and obtained a lease, information about this lease is stored in /var/
lib/dhclient/dhclient-interface.leases.
For more information, see the dhclient(8) manual page.
12.4 About Network Address Translation
Network Address Translation (NAT) assigns a public address to a computer or a group of computers
inside a private network with a different address scheme. The public IP address masquerades all requests
as going to one server rather than several servers. NAT is useful for limiting the number of public IP
addresses that an organization must finance, and for providing extra security by hiding the details of
internal networks.
The netfilter kernel subsystem provides the nat table to implement NAT in addition to its tables
for packet filtering. The kernel consults the nat table whenever it handles a packet that creates a new
incoming or outgoing connection.
Note
If your want a system to be able to route packets between two of its network
interfaces, you must turn on IP forwarding:
# echo 1 > /proc/sys/net/ipv4/ip_forward
The NAT table includes the following built-in rule chains:
PREROUTING
Handles packets arriving from external networks.
OUTPUT
Handles packets generated on the host system before sending them externally.
POSTROUTING
Handles packets arriving from local systems before sending them externally.
The NAT table has the following targets that can be used with the rule chains:
DNAT
Alters the destination IP address and port of an incoming packet to route it to a different
host.
SNAT
Alters the source IP address and port on an outgoing packet so that it appears to come
from a different host.
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About Network Address Translation
MASQUERADE
Masks the private IP address of a node with the external IP address of the firewall or
gateway router.
The following example specifies that NAT should use the PREROUTING chain to forward incoming HTTP
requests on the eth0 interface to port 8080 of the dedicated HTTP server 192.168.1.100. The rule
changes the destination address and port of the packet.
# iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 \
-j DNAT --to 192.168.1.100:8080
The following example allows nodes on the LAN with private IP addresses to communicate with external
public networks:
# iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
This rule makes requests from internal systems appear to originate from the IP address of the firewall’s
external interface (eth1).
You can also use the Firewall Configuration GUI (system-config-firewall) to configure simple
masquerading and port forwarding.
For more information, see the iptables(8) manual page.
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Chapter 13 Name Service Configuration
Table of Contents
13.1 About DNS and BIND .............................................................................................................
13.2 About Types of Name Servers .................................................................................................
13.3 About DNS Configuration Files ................................................................................................
13.3.1 /etc/named.conf ............................................................................................................
13.3.2 About Resource Records in Zone Files .........................................................................
13.3.3 About Resource Records for Reverse-name Resolution .................................................
13.4 Configuring a Name Server .....................................................................................................
13.5 Administering the Name Service ..............................................................................................
13.6 Performing DNS Lookups ........................................................................................................
127
128
128
128
131
132
133
134
135
This chapter describes how to use BIND to set up a DNS name server.
13.1 About DNS and BIND
The Domain Name System (DNS) is a network-based service that maps (resolves) domain names to
IP addresses. For a small, isolated network, you could use entries in the /etc/hosts file to provide the
mapping, but most networks that are connected to the Internet use DNS.
DNS is a hierarchical and distributed database, where each level of the hierarchy is delimited by a period
(.). Consider the following fully qualified domain name (FQDN):
wiki.us.mydom.com.
The root domain, represented by the final period in the FQDN, is usually omitted, except in DNS
configuration files:
wiki.us.mydom.com
In this example, the top-level domain is com, mydom is a subdomain of com, us is a subdomain of mydom,
and wiki is the host name. Each of these domains are grouped into zones for administrative purposes.
A DNS server, or name server, stores the information that is needed to resolve the component domains
inside a zone. In addition, a zone's DNS server stores pointers to the DNS servers that are responsible for
resolving each subdomain.
If a client outside the us.mydom.com domain requests that its local name server resolve a FQDN such as
wiki.us.mydom.com into an IP address for which the name server is not authoritative, the name server
queries a root name server for the address of a name server that is authoritative for the com domain.
Querying this name server returns the IP address of a name server for mydom.com. In turn, querying this
name server returns the IP address of the name server for us.oracle.com, and querying this final name
server returns the IP address for the FQDN. This process is known as a recursive query, where the local
name server handles each referral from an external name server to another name server on behalf of the
resolver.
Iterative queries rely on the resolver being able to handle the referral from each external name server to
trace the name server that is authoritative for the FQDN. Most resolvers use recursive queries and so
cannot use name servers that support only iterative queries. Fortunately, most
Oracle Linux provides the Berkeley Internet Name Domain (BIND) implementation of DNS. The bind
package includes the DNS server daemon (named), tools for working with DNS such as rndc, and a
number of configuration files, including:
127
About Types of Name Servers
/etc/named.conf
Contains settings for named and lists the location and characteristics of
the zone files for your domain. Zone files are usually stored in /var/
named.
/etc/named.rfc1912.zones
Contains several zone sections for resolving local loopback names and
addresses.
/var/named/named.ca
Contains a list of the root authoritative DNS servers.
13.2 About Types of Name Servers
You can configure several types of name server using BIND, including:
Master name server
Authoritative for one or more domains, a master name server maintains
its zone data in several database files, and can transfer this information
periodically to any slave name servers that are also configured in the
zone. In older documentation, master name servers are known as
primary name servers. An organization might maintain two master name
servers for a zone: one master outside the firewall to provide restricted
information about the zone for publicly accessible hosts and services,
and a hidden or stealth master inside the firewall that holds details of
internal hosts and services.
Slave name server
Acting as a backup to a master name server, a slave name server
maintains a copy of the zone data, which it periodically refreshes from
the master's copy. In older documentation, slave name servers are
known as secondary name servers.
Stub name server
A master name server for a zone might also be configured as a stub
name server that maintains information about the master and slave
name servers of child zones.
Caching-only name server
Performs queries on behalf of a client and stores the responses in a
cache after returning the results to the client. It is not authoritative for
any domains and the information that it records is limited to the results
of queries that it has cached.
Forwarding name server
Forwards all queries to another name server and caches the results,
which reduces local processing, external access, and network traffic.
In practice, a name server can be a combination of several of these types in complex configurations.
13.3 About DNS Configuration Files
Domains are grouped into zones and zones are configured through the use of zone files. Zone files store
information about domains in the DNS database. Each zone file contains directives and resource records.
Optional directives apply settings to a zone or instruct a name server to perform certain tasks. Resource
records specify zone parameters and define information about the systems (hosts) in a zone.
For examples of BIND configuration files, see /usr/share/doc/bind-version/sample/ .
13.3.1 /etc/named.conf
The main configuration file for named is /etc/named.conf, which contains settings for named and the
top-level definitions for zones, for example:
include "/etc/rndc.key";
128
/etc/named.conf
controls {
inet 127.0.0.1 allow { localhost; } keys { "rndc-key"; }
};
zone "us.mydom.com" {
type master;
file "data/master-data";
allow-update { key "rndc-key"; };
notify yes;
};
zone "mydom.com" in{
type slave;
file "sec/sec.slave-data";
allow-update { key "rndc-key"; };
masters {10.1.32.1;};
};
zone "2.168.192.in-addr.arpa" IN {
type master;
file "data/reverse-192.168.2";
allow-update { key “rndc-key”; };
notify yes;
};
The include statement allows external files to be referenced so that potentially sensitive data such as key
hashes can be placed in a separate file with restricted permissions.
The controls statement defines access information and the security requirements that are necessary to
use the rndc command with the named server:
inet
Specifies which hosts can run rndc to control named. In this example, rndc must be run on the
local host (127.0.0.1).
keys
Specifies the names of the keys that can be used. The example specifies using the key named
rndc-key, which is defined in /etc/rndc.key. Keys authenticate various actions by named and
are the primary method of controlling remote access and administration.
The zone statements define the role of the server in different zones.
The following zone options are used:
type
Specifies that this system is the master name server for the zone us.mydom.com and
a slave server for mydom.com. 2.168.192.in-addr.arpa is a reverse zone for
resolving IP addresses to host names. See Section 13.3.3, “About Resource Records for
Reverse-name Resolution ”.
file
Specifies the path to the zone file relative to /var/named. The zone file for
us.mydom.com is stored in /var/named/data/master-data and the transferred
zone data for mydom.com is cached in /var/named/data/slave-data.
allow-update
Specifies that a shared key must exist on both the master and a slave name server for
a zone transfer to take place from the master to the slave. The following is an example
record for a key in /etc/rndc.key:
key "rndc-key" {
algorithm hmac-md5;
secret "XQX8NmM41+RfbbSdcqOejg==";
};
You can use the rndc-confgen -a command to generate a key file.
129
/etc/named.conf
notify
Specifies whether to notify the slave name servers when the zone information is
updated.
masters
Specifies the master name server for a slave name server.
The next example is taken from the default /etc/named.conf file that is installed with the bind package,
and which configures a caching-only name server.
options {
listen-on port 53 { 127.0.0.1; };
listen-on-v6 port 53 { ::1; };
directory
"/var/named";
dump-file
"/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
allow-query { localnets; };
recursion yes;
dnssec-enable yes;
dnssec-validation yes;
dnssec-lookaside auto;
/* Path to ISC DLV key */
bindkeys-file "/etc/named.iscdlv.key";
managed-keys-directory "/var/named/dynamic";
};
logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};
zone "." IN {
type hint;
file "named.ca";
};
include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";
The options statement defines global server configuration options and sets defaults for other statements.
listen-on
The port on which named listens for queries.
directory
Specifies the default directory for zone files if a relative pathname is
specified.
dump-file
Specifies where named dumps its cache if it crashes.
statistics-file
Specifies the output file for the rndc stats command.
memstatistics-file
Specifies the output file for named memory-usage statistics.
allow-query
Specifies which IP addresses may query the server. localnets
specifies all locally attached networks.
recursion
Specifies whether the name server performs recursive queries.
dnssec-enable
Specifies whether to use secure DNS (DNSSEC).
dnssec-validation
Whether the name server should validate replies from DNSSECenabled zones.
130
About Resource Records in Zone Files
Whether to enable DNSSEC Lookaside Validation (DLV) using the key
in /etc/named.iscdlv.key defined by bindkeys-file.
dnssec-lookaside
The logging section enables logging of messages to /var/named/data/named.run. The severity
parameter controls the logging level, and the dynamic value means that this level can be controlled by
using the rndc trace command.
The zone section specifies the initial set of root servers using a hint zone. This zone specifies that named
should consult /var/named/named.ca for the IP addresses of authoritative servers for the root domain
(.).
For more information, see the named.conf(5) manual page and the BIND documentation in /usr/
share/doc/bind-version/arm.
13.3.2 About Resource Records in Zone Files
A resource record in a zone file contains the following fields, some of which are optional depending on the
record type:
Name
Domain name or IP address.
TTL (time to live)
The maximum time that a name server caches a record before it checks
whether a newer one is available.
Class
Always IN for Internet.
Type
Type of record, for example:
Data
A (address)
IPv4 address corresponding to a host.
AAAA (address)
IPv6 address corresponding to a host.
CNAME (canonical name)
Alias name corresponding to a host name.
MX (mail exchange)
Destination for email addressed to the
domain.
NS (name server)
Fully qualified domain name of an
authoritative name server for a domain.
PTR (pointer)
Host name corresponding to an IP address
for address to name lookups (reverse-name
resolution).
SOA (start of authority)
Authoritative information about a zone,
such as the master name server, the email
address of the domain's administrator, and
the domain's serial number. All records
following a SOA record relate to the zone that
it defines up to the next SOA record.
The information that the record stores, such as an IP address in an A record, or
a host name in a CNAME or PTR record.
The following example shows the contents of a typical zone file such as /var/named/data/masterdata:
$TTL 86400
; 1 day
131
About Resource Records for Reverse-name Resolution
@ IN SOA dns.us.mydom.com. root.us.mydom.com. (
57 ; serial
28800 ; refresh (8 hours)
7200 ; retry (2 hours)
2419200 ; expire (4 weeks)
86400 ; minimum (1 day)
)
IN NS
dns.us.mydom.com.
dns
us.mydom.com
svr01
www
host01
host02
host03
...
IN
IN
IN
IN
IN
IN
IN
A
A
A
CNAME
A
A
A
192.168.2.1
192.168.2.1
192.168.2.2
svr01
192.168.2.101
192.168.2.102
192.168.2.103
A comment on a line is preceded by a semicolon (;).
The $TTL directive defines the default time-to-live value for all resource records in the zone. Each resource
record can define its own time-to-live value, which overrides the global setting.
The SOA record is mandatory and included the following information:
us.mydom.com
The name of the domain.
dns.us.mydom.com.
The fully qualified domain name of the name server, including a trailing period
(.) for the root domain.
root.us.mydom.com.
The email address of the domain administrator.
serial
A counter that, if incremented, tells named to reload the zone file.
refresh
The time after which a master name server notifies slave name servers that they
should refresh their database.
retry
If a refresh fails, the time that a slave name server should wait before attempting
another refresh.
expire
The maximum elapsed time that a slave name server has to complete a refresh
before its zone records are no longer considered authoritative and it will stop
answering queries.
minimum
The minimum time for which other servers should cache information obtained
from this zone.
An NS record declares an authoritative name server for the domain.
Each A record specifies the IP address that corresponds to a host name in the domain.
The CNAME record creates the alias www for svr01.
For more information, see the BIND documentation in /usr/share/doc/bind-version/arm.
13.3.3 About Resource Records for Reverse-name Resolution
Forward resolution returns an IP address for a specified domain name. Reverse-name resolution returns
a domain name for a specified IP address. DNS implements reverse-name resolution by using the special
in-addr.arpa and ip6.arpa domains for IPv4 and IPv6.
132
Configuring a Name Server
The characteristics for a zone's in-addr.arpa or ip6.arpa domains are usually defined in /etc/
named.conf, for example:
zone "2.168.192.in-addr.arpa" IN {
type master;
file "data/reverse-192.168.2";
allow-update { key “rndc-key”; };
notify yes;
};
The zone's name consists of in-addr.arpa preceded by the network portion of the IP address for the
domain with its dotted quads written in reverse order.
If your network does not have a prefix length that is a multiple of 8, see RFC 2317 for the format that you
should use instead.
The PTR records in in-addr.arpa or ip6.arpa domains define host names that correspond to
the host portion of the IP address. The following example is take from the /var/named/data/
reverse-192.168.2 zone file:
$TTL 86400
;
@ IN SOA dns.us.mydom.com. root.us.mydom.com. (
57 ;
28800 ;
7200 ;
2419200 ;
86400 ;
)
IN NS
dns.us.mydom.com.
1
1
2
101
102
103
...
IN
IN
IN
IN
IN
IN
PTR
PTR
PTR
PTR
PTR
PTR
dns
us.mydom.com
svr01
host01
host02
host03
For more information, see the BIND documentation in /usr/share/doc/bind-version/arm.
13.4 Configuring a Name Server
By default, the BIND installation allows you to configure a caching-only name server using the
configuration settings that are provided in /etc/named.conf and files that it includes. This procedure
assumes that you will either use the default settings or configure new named configuration and zone files.
To configure a name server:
1. Install the bind package:
# yum install bind
2. If NetworkManager is enabled on the system, edit the /etc/sysconfig/network-scripts/
ifcfg-interface file, and add the following entry:
DNS1=127.0.0.1
This line causes NetworkManager to add the following entry to /etc/resolv.conf when the
network service starts:
nameserver 127.0.0.1
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Administering the Name Service
This entry points the resolver at the local name server.
If you have disabled NetworkManager, edit /etc/resolv.conf to include the nameserver
127.0.0.1 entry.
3. If required, modify the named configuration and zone files.
4. Allow incoming TCP connections to port 53 and incoming UDP datagrams on port 53 from the local
network:
# iptables -I INPUT -s subnet_addr/prefix_length -p tcp \
-m state --state NEW -m tcp -–dport 53 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p udp \
-m udp -–dport 53 -j ACCEPT
# service iptables save
where subnet_addr/prefix_length specifies the network address, for example
192.168.1.0/24.
5. Restart the network service, restart the named service, and configure named to start following system
reboots:
# service network restart
# service named start
# chkconfig named on
13.5 Administering the Name Service
The rndc command allows you to administer the named service, either locally or from a remote machine (if
permitted in the controls section of the /etc/named.conf file). To prevent unauthorized access to the
service, rndc must be configured to listen on the selected port (by default, port 953), and both named and
rndc must have access to the same key. To generate a suitable key, use the rndc-confgen command:
# rndc-confgen –a
wrote key file "/etc/rndc.key"
To ensure that only root can read the file:
# chmod o-rwx /etc/rndc.key
To check the status of the named service:
# rndc status
number of zones: 3
debug level: 0
xfers running: 0
xfers deferred: 0
soa queries in progress: 0
query logging is OFF
recursive clients: 0/1000
tcp clients: 0/100
server is up and running
If you modify the named configuration file or zone files, rndc reload instructs named to reload the files:
# rndc reload
server reload successful
For more information, see the named(8), rndc(8) and rndc-confgen(8) manual pages.
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Performing DNS Lookups
13.6 Performing DNS Lookups
The host utility is recommended for performing DNS lookups. Without any arguments, host displays a
summary of its command-line arguments and options. For example, look up the IP address for host01:
$ host host01
Perform a reverse lookup for the domain name that corresponds to an IP address:
$ host 192.168.2.101
Query DNS for the IP address that corresponds to a domain:
$ host dns.us.mydoc.com
Use the -v and -t options to display verbose information about records of a certain type:
$ host -v -t MX www.mydom.com
Trying "www.mydom.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49643
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;www.mydom.com.
IN MX
;; ANSWER SECTION:
www.mydom.com. 135 IN CNAME www.mydom.com.acme.net.
www.mydom.com.acme.net. 1240 IN CNAME d4077.c.miscacme.net.
;; AUTHORITY SECTION:
c.miscacme.net. 2000 IN SOA m0e.miscacme.net. hostmaster.misc.com. ...
Received 163 bytes from 10.0.0.1#53 in 40 ms
The –a option (equivalent to -v -t ANY) displays all available records for a zone:
$ host -a www.us.mydom.com
Trying "www.us.mydom.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 40030
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.us.mydom.com.
IN ANY
;; ANSWER SECTION:
www.us.mydom.com. 263 IN CNAME www.us.mydom.acme.net.
Received 72 bytes from 10.0.0.1#53 in 32 ms
For more information, see the host(1) manual page.
135
136
Chapter 14 Network Time Configuration
Table of Contents
14.1 About the NTP Daemon ..........................................................................................................
14.1.1 Configuring the ntpd Service .........................................................................................
14.2 About PTP ..............................................................................................................................
14.2.1 Configuring the PTP Service .........................................................................................
14.2.2 Using PTP as a Time Source for NTP ...........................................................................
137
137
138
139
141
This chapter describes how to configure a system to use the Network Time Protocol (NTP) or Precision
Time Protocol (PTP) daemons for setting the system time.
14.1 About the NTP Daemon
The ntpd daemon can synchronise the system clock with remote NTP servers, with local reference clocks,
or with GPS and radio time signals. ntpd provides a complete implementation of NTP version 4 (RFC
5905) and is also compatibility with versions 3 (RFC 1305), 2 (RFC 1119), and 1 (RFC 1059).
You can configure ntpd to run in several different modes, as described at http://doc.ntp.org/4.2.6p5/
assoc.html, using both symmetric-key and public-key cryptography, as described at http://
doc.ntp.org/4.2.6p5/authopt.html.
14.1.1 Configuring the ntpd Service
To configure the ntpd service on a system:
1. Install the ntp package.
# yum install ntp
2. Edit /etc/ntp.conf to set up the configuration for ntpd.
Note
The default configuration assumes that the system has network access to public
NTP servers with which it can synchronise. The firewall rules for your internal
networks might well prevent access to these servers but instead allow access to
local NTP servers.
The following example shows a sample NTP configuration for a system that can access three NTP
servers:
server NTP_server_1
server NTP_server_2
server NTP_server_3
server 127.127.1.0
fudge
127.127.1.0 stratum 10
driftfile /var/lib/ntp/drift
restrict default nomodify notrap nopeer noquery
The server and fudge entries for 127.127.1.0 cause ntpd to use the local system clock if the remote
NTP servers are not available. The restrict entry allows remote systems only to synchronise their
time with the local NTP service.
For more information about configuring ntpd, see http://doc.ntp.org/4.2.6p5/manyopt.html.
137
About PTP
3. Create the drift file.
# touch /var/lib/ntp/drift
4. If remote access to the local NTP service is required, configure the system firewall to allow access to
the NTP service on UDP port 123, for example:
# iptables -I INPUT -p udp -m udp --dport 123 -j ACCEPT
# service iptables save
5. Start the ntpd service and configure it to start following a system reboot.
# service ntpd start
# chkconfig ntpd on
You can use the ntpq and ntpstat commands to display information about the operation of ntpd, for
example:
# ntpq -p
remote
refid
st t when poll reach
delay
offset jitter
==============================================================================
*ns1.proserve.nl 193.67.79.202
2 u
21
64 377
31.420
10.742
3.689
-pomaz.hu
84.2.46.19
3 u
22
64 377
59.133
13.719
5.958
+server.104media 193.67.79.202
2 u
24
64 377
32.110
13.436
5.222
+public-timehost 193.11.166.20
2 u
28
64 377
57.214
9.304
6.311
# ntpstat
synchronised to NTP server (80.84.224.85) at stratum 3
time correct to within 76 ms
polling server every 64
For more information, see the ntpd(8), ntpd.conf(5), ntpq(8), and ntpstat(8) manual pages and
http://doc.ntp.org/4.2.6p5/.
14.2 About PTP
PTP allows you to synchronise system clocks on a local area network to a higher accuracy than NTP.
Provided that network drivers support either hardware or software time stamping, a PTP clock can use
the time stamps in PTP messages to compensate for propagation delays across a network. Software
time stamping allows PTP to synchronise systems to within a few tens of microseconds. With hardware
time stamping, PTP can synchronise systems to within a few tenths of a microsecond. If you require highprecision time synchronization of systems, use hardware time stamping. Both the UEK R3 and RHCK
kernels support PTP version 2 as defined in IEEE 1588.
A typical PTP configuration on an enterprise local area network consists of:
• One or more grandmaster clock systems.
A grandmaster clock is typically implemented as specialized hardware that can use high-accuracy GPS
signals or lower-accuracy code division multiple access (CDMA) signals, radio clock signals, or NTP
as a time reference source. If several grandmaster clocks are available, the best master clock (BMC)
algorithm selects the grandmaster clock based on the settings of their priority1, clockClass,
clockAccuracy, offsetScaledLogVariance, and priority2 parameters and their unique
identifier, in that order.
• Several boundary clock systems.
Each boundary clock is slaved to a grandmaster clock on one subnetwork and relays PTP messages to
one or more additional subnetworks. A boundary clock is usually implemented as a function of a network
switch.
• Multiple slave clock systems.
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Configuring the PTP Service
Each slave clock on a subnetwork is slaved to a boundary clock, which acts as the master clock for that
slave clock.
A simpler configuration is to set up a single grandmaster clock and multiple slave clocks on the same
network segment, which removes any need for an intermediate layer of boundary clocks.
Grandmaster and slave clock systems, which use only one network interface for PTP, are termed ordinary
clocks.
Boundary clocks require at least two network interfaces for PTP: one interface acts a slave to a
grandmaster clock or a higher-level boundary clock; the other interfaces act as masters to slave clocks or
lower-level boundary clocks.
Synchronization of boundary and slave clock systems is achieved by sending time stamps in PTP
messages. By default, PTP messages are sent in UDPv4 datagrams. It is also possible to configure PTP to
use UDPv6 datagrams or Ethernet frames as its transport mechanism.
To be able to use PTP with a system, the driver for at least one of the system's network interfaces must
support either software or hardware time stamping. To find out whether the driver for a network interface
supports time stamping, use the ethtool command as shown in the following example:
# ethtool -T em1
Time stamping parameters for em1:
Capabilities:
hardware-transmit
(SOF_TIMESTAMPING_TX_HARDWARE)
software-transmit
(SOF_TIMESTAMPING_TX_SOFTWARE)
hardware-receive
(SOF_TIMESTAMPING_RX_HARDWARE)
software-receive
(SOF_TIMESTAMPING_RX_SOFTWARE)
software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
hardware-raw-clock
(SOF_TIMESTAMPING_RAW_HARDWARE)
...
The output from ethtool in this example shows that the em1 interface supports both hardware and
software time stamping capabilities.
With software time stamping, ptp4l synchronises the system clock to an external grandmaster clock.
If hardware time stamping is available, ptp4l can synchronise the PTP hardware clock to an external
grandmaster clock. In this case, you use the phc2sys daemon to synchronise the system clock with the
PTP hardware clock.
14.2.1 Configuring the PTP Service
To configure the PTP service on a system:
1. Install the linuxptp package.
# yum install linuxptp
2. Edit /etc/sysconfig/ptp4l and define the start-up options for the ptp4l daemon.
Grandmaster clocks and slave clocks require that you define only one interface.
For example, to use hardware time stamping with interface em1 on a slave clock:
OPTIONS="-f /etc/ptp4l.conf -i em1 -s"
To use software time stamping instead of hardware time stamping, specify the -S option:
OPTIONS="-f /etc/ptp4l.conf -i em1 -S -s"
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Configuring the PTP Service
Note
The -s option specifies that the clock operates only as a slave (slaveOnly
mode). Do not specify this option for a grandmaster clock or a boundary clock.
For a grandmaster clock, omit the -s option, for example:
OPTIONS="-f /etc/ptp4l.conf -i em1"
A boundary clock requires that you define at least two interfaces, for example:
OPTIONS="-f /etc/ptp4l.conf -i em1 -i em2"
You might need to edit the file /etc/ptp4l.conf to make further adjustments to the configuration of
ptp4l, for example:
• For a grandmaster clock, set the value of the priority1 parameter to a value between 0 and 127,
where lower values have higher priority when the BMC algorithm selects the grandmaster clock. For
a configuration that has a single grandmaster clock, a value of 127 is suggested.
• If you set the value of summary_interval to an integer value N instead of 0, ptp4l writes
N
0
summary clock statistics to /var/log/messages every 2 seconds instead of every second (2 =
10
1). For example, a value of 10 would correspond to an interval of 2 or 1024 seconds.
• The logging_level parameter controls the amount of logging information that ptp4l records.
The default value of logging_level is 6, which corresponds to LOG_INFO. To turn off logging
completely, set the value of logging_level to 0. Alternatively, specify the -q option to ptp4l.
For more information, see the ptp4l(8) manual page.
3. Configure the system firewall to allow access by PTP event and general messages to UDP ports 319
and 320, for example:
# iptables -I INPUT -p udp -m udp --dport 319 -j ACCEPT
# iptables -I INPUT -p udp -m udp --dport 320 -j ACCEPT
# service iptables save
4. Start the ptp4l service and configure it to start following a system reboot.
# service ptp4l start
# chkconfig ptp4l on
5. To configure phc2sys on a clock system that uses hardware time stamping:
a. Edit /etc/sysconfig/phc2sys and define the start-up options for the phc2sys daemon.
On a boundary clock or slave clock, synchronise the system clock with the PTP hardware clock that
is associated with the slave network interface, for example:
OPTIONS="-c CLOCK_REALTIME -s em1 -w"
Note
The slave network interface on a boundary clock is the one that it uses to
communicate with the grandmaster clock.
The -w option specifies that phc2sys waits until ptp4l has synchronised the PTP hardware clock
before attempting to synchronise the system clock.
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Using PTP as a Time Source for NTP
On a grandmaster clock, which derives its system time from a reference time source such as GPS,
CDMA, NTP, or a radio time signal, synchronise the network interface's PTP hardware clock from
the system clock, for example:
OPTIONS="-c em1 -s CLOCK_REALTIME -w"
For more information, see the phc2sys(8) manual page.
b. Start the phc2sys service and configure it to start following a system reboot.
# service phc2sys start
# chkconfig phc2sys on
You can use the pmc command to query the status of ptp4l operation. The following example shows the
results of running pmc on a slave clock system that is directly connected to the grandmaster clock system
without any intermediate boundary clocks:
# pmc -u -b 0 'GET TIME_STATUS_NP'
sending: GET TIME_STATUS_NP
080027.fffe.7f327b-0 seq 0 RESPONSE MANAGEMENT TIME_STATUS_NP
master_offset
-98434
ingress_time
1412169090025854874
cumulativeScaledRateOffset +1.000000000
scaledLastGmPhaseChange
0
gmTimeBaseIndicator
0
lastGmPhaseChange
0x0000'0000000000000000.0000
gmPresent
true
gmIdentity
080027.fffe.d9e453
# pmc -u -b 0 'GET CURRENT_DATA_SET'
sending: GET CURRENT_DATA_SET
080027.fffe.7f327b-0 seq 0 RESPONSE MANAGEMENT CURRENT_DATA_SET
stepsRemoved
1
offsetFromMaster 42787.0
meanPathDelay
289207.0
Useful information in this output includes:
gmIdentity
The unique identifier of the grandmaster clock, which is based on the MAC address
of its network interface.
gmPresent
Whether an external grandmaster clock is available. This value is displayed as
false on the grandmaster clock itself.
meanPathDelay
An estimate of how many nanoseconds by which synchronization messages are
delayed.
offsetFromMaster
The most recent measurement of the time difference in nanoseconds relative to the
grandmaster clock.
stepsRemoved
The number of network steps between this system and the grandmaster clock.
For more information, see the phc2sys(8), pmc(8), and ptp4l(8) manual pages, http://www.zhaw.ch/
en/engineering/institutes-centres/ines/downloads/documents.html, and IEEE 1588.
14.2.2 Using PTP as a Time Source for NTP
To make the PTP-adjusted system time on an NTP server available to NTP clients, include the following
entries in /etc/ntp.conf on the NTP server to define the local system clock as the time reference:
server
127.127.1.0
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Using PTP as a Time Source for NTP
fudge
127.127.1.0 stratum 0
Note
Do not configure any additional server lines in the file.
For more information, see Section 14.1.1, “Configuring the ntpd Service”.
142
Chapter 15 Web Service Configuration
Table of Contents
15.1
15.2
15.3
15.4
15.5
About the Apache HTTP Server ..............................................................................................
Installing the Apache HTTP Server ..........................................................................................
Configuring the Apache HTTP Server ......................................................................................
Testing the Apache HTTP Server ............................................................................................
Configuring Apache Containers ...............................................................................................
15.5.1 About Nested Containers ..............................................................................................
15.6 Configuring Apache Virtual Hosts ............................................................................................
143
143
143
146
146
147
148
This chapter describes how to configure a basic HTTP server.
15.1 About the Apache HTTP Server
Oracle Linux provides the Apache HTTP Server, which is an open-source web server developed by the
Apache Software Foundation. The Apache server hosts web content, and responds to requests for this
content from web browsers such as Firefox.
15.2 Installing the Apache HTTP Server
To install the Apache HTTP server:
1. Enter the following command:
# yum install httpd
2. Start the server, and configure it to start after system reboots:
# service httpd start
# chkconfig httpd on
3. Check for configuration errors:
# service httpd configtest
15.3 Configuring the Apache HTTP Server
Note
Any changes that you make to the configuration of the Apache HTTP server do not
take effect until you restart the server:
# service httpd restart
The main configuration file for the Apache HTTP server is /etc/httpd/conf/httpd.conf. You can
modify the directives in this file to customize Apache for your environment.
The directives include:
Allow from client
[client ...] | all
Specifies a list of clients that can access content or all to serve
content to any client. The Order directive determines the order in which
httpd evaluates Allow and Deny directives.
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Configuring the Apache HTTP Server
Deny from client [client
...] | all
Specifies a list of clients that cannot access content or all to disallow
all clients. The Order directive determines the order in which httpd
evaluates Allow and Deny directives.
DocumentRoot directorypath
The top level directory for Apache server content. The apache user
requires read access to any files and read and execute access to the
directory and any of its sub-directories. Do not place a slash at the end
of the directory path.
For example:
DocumentRoot /var/www/html
ErrorLog filename |
syslog[:facility]
If set to a file name, specifies the file, relative to ServerRoot, to which
httpd sends error messages.
If set to syslog, specifies that httpd send errors to rsyslogd. A
facility argument specifies the rsyslogd facility. The default facility
is local7.
For example:
ErrorLog logs/error_log
Listen [IP_address:]port
Accept incoming requests on the specified port or IP address and port
combination. By default, the httpd server accepts requests on port
80 for all network interfaces. For a port number other than 80, HTTP
requests to the server must include the port number.
For example:
Listen 80
Listen 192.168.2.1:8080
LoadModule module path
The Apache HTTP server can load external modules (dynamic shared
objects or DSOs) to extend its functionality. The module argument is
the name of the DSO, and filename is the path name of the module
relative to ServerRoot.
For example:
LoadModule auth_basic_module modules/mod_auth_basic.so
Order deny,allow |
allow,deny
Specifies the order in which httpd evaluates Allow and Deny
directives.
For example, permit access only to clients from the mydom.com
domain:
Order deny,allow
Deny from all
Allow from .mydom.com
The following directives would not permit access by any client:
Order allow,deny
Deny from all
Allow from .mydom.com
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Configuring the Apache HTTP Server
ServerName FQDN[:port]
Specifies the fully qualified domain name or IP address of the httpd
server and an optional port on which the server listens. The FQDN
must be resolvable to an IP address. If you do not specify a FQDN, the
server performs a reverse-name lookup on the IP address. If you do not
specify a port, the server uses the port corresponding to the incoming
request.
For example:
ServerName www.mydom.com:80
ServerRoot directorypath
The top of the directory hierarchy where the httpd server keeps its
configuration, error, and log files. Do not place a slash at the end of the
directory path.
For example:
ServerRoot /etc/httpd
Timeout seconds
Specifies the number of seconds that httpd waits for network
operations to finish before reporting a timeout error. The default value is
60 seconds.
UserDir directory-path
... | disabled [user
...] | enabled user ...
If set to disabled, disallows users identified by the space-separated
user argument to publish content from their home directories. If no
users are specified, all users are disallowed.
If set to enabled, allows users identified by the space-separated user
argument to publish content from their home directories, provided that
they are not specified as an argument to disabled.
directory-path is the name of a directory from which httpd
publishes content. A relative path is assumed to be relative to a user’s
home directory. If you specify more than one directory path, httpd tries
each alternative in turn until find a web page. If directory-path is
not defined, the default is ~/public_html. Do not place a slash at the
end of the directory path.
For example:
UserDir disabled root guest
UserDir enabled oracle alice
UserDir www http://www.mydom.com/
The root and guest users are disabled from content publishing.
Assuming that ServerName is set to www.mydom.com, browsing
http://www.example.com/~alice displays alice's web
page, which must be located at ~alice/www or http://
www.example.com/alice (that is, in the directory alice relative to
ServerRoot).
Note
You would usually change the settings in the
<IfModule mod_userdir.c> container to
allow users to publish user content.
For more information, see http://httpd.apache.org/docs/current/mod/directives.html.
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Testing the Apache HTTP Server
15.4 Testing the Apache HTTP Server
To test that an Apache HTTP server is working:
• From the local system, direct a browser on the local system to http://localhost.
• From a remote system, direct a browser to http:// followed by the value of the ServerName directive
specified in the configuration file (/etc/httpd/conf/httpd.conf).
If the browser displays the Apache 2 Test Page, the server is working correctly.
To test that the server can deliver content, create an HTML file named index.html in the directory
specified by the DocumentRoot directive (by default, /var/www/html). After reloading the page, the
browser should display this HTML file instead of the Apache 2 Test Page.
15.5 Configuring Apache Containers
Apache containers are special directives that group other directives, often to create separate web directory
hierarchies with different characteristics. A container is delimited by the XML-style tags <type> and
</type>, where type is the container type.
The following are examples of container types:
<Directory directorypath>
Applies the contained directives to directories under directory-path.
The following example applies the Deny, Allow, and AllowOverride
directives to all files and directories under /var/www/html/sandbox.
<Directory /var/www/html/sandbox>
Deny from all
Allow from 192.168.2.
AllowOverride All
</Directory>
The AllowOverride directive is only used in Directory
containers and specifies which classes of directives are allowed in
.htaccess files. (.htaccess configuration files typically contain user
authentication directives for a web directory.) The directive classes
control such aspects as authorization, client access, and directory
indexing. You can specify the argument All to permit all classes
of directives in .htaccess files, a space-separated list of directive
classes to permit only those classes, or None to make the server ignore
.htaccess files altogether.
Note
If SELinux is enabled on the system, you must
change the default file type if the file system
hierarchy specified by <Directory> is not
under /var/www/html.
<IfModule [!]module>
Applies directives if the specified module has been loaded, or, when the
exclamation point (!) is specified, if the module has not been loaded.
The following example disallows user-published content if
mod_userdir.c has been loaded:
<IfModule mod_userdir.c>
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About Nested Containers
UserDir disabled
</IfModule>
Places limits on the specified HTTP methods (such as GET, OPTIONS,
POST, and PUT) for use with a Uniform Resource Identifier (URI).
<Limit method ...>
The following example limits systems in mydom.com to using only the
GET and PUT methods to perform HTTP downloads and uploads:
<Limit GET PUT>
Order deny,allow
Deny from all
Allow from .example.com
</Limit>
Systems outside mydom.com cannot use GET and PUT with the URI.
<LimitExcept method ...>
Places limits on all except the specified HTTP methods for use with a
Uniform Resource Identifier (URI).
The following example disallows any system from using any method
other than GET and POST:
<LimitExcept GET POST>
Order deny,allow
Deny from all
</Limit>
VirtualHost
IP_address:port ...
Specifies a group of directives that define a container for a virtual host.
See Section 15.6, “Configuring Apache Virtual Hosts”.
15.5.1 About Nested Containers
The following example illustrates how you can nest containers, using <Limit> and <LimitExcept>
containers to permit GET, POST, and OPTIONS to be used with user directories under /home/*/
public_html.
<Directory /home/*/public_html>
AllowOverride FileInfo AuthConfig Limit
Options MultiViews Indexes SymLinksIfOwnerMatch \
IncludesNoExec
<Limit GET POST OPTIONS>
Order allow,deny
Allow from all
</Limit>
<LimitExcept GET POST OPTIONS>
Order deny,allow
Deny from all
</LimitExcept>
</Directory>
In the example, the AllowOverride directive specifies the following directive classes:
AuthConfig
Permits the use of the authorization directives.
FileInfo
Permits the use of directives that control document types.
Limit
Permits the use of directives that control host access.
The Options directive controls the features of the server for the directory hierarchy, for example:
FollowSymLinks
Follow symbolic links under the directory hierarchy.
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Configuring Apache Virtual Hosts
Includes
Permits server-side includes.
IncludesNoExec
Prevents the server from running #exec cmd and #exec cgi server-side
includes.
Indexes
Generates a web directory listing if the DirectoryIndex directive is not set.
MultiViews
Allows the server to determine the file to use that best matches the client's
requirements based on the MIME type when several versions of the file exist
with different extensions.
SymLinksIfOwnerMatch
Allows the server to follow a symbolic link if the file or directory being pointed
to has the same owner as the symbolic link.
For more information, see http://httpd.apache.org/docs/current/mod/directives.html.
15.6 Configuring Apache Virtual Hosts
The Apache HTTP server supports virtual hosts, meaning that it can respond to requests that are directed
to multiple IP addresses or host names that correspond to the same host machine. You can configure each
virtual host to provide different content and to behave differently.
You can configure virtual hosts in two ways:
• IP-based Virtual Hosts (host-by-IP)
Each virtual host has its own combination of IP address and port. The server responds to the IP
address with which the host name resolves. Host-by-IP is needed to server HTTPS requests because of
restrictions in the SSL (Secure Sockets Layer) protocol.
• Name-based Virtual Hosts (host-by-name)
All virtual hosts share a common IP address. Apache responds to the request by mapping the host name
in the request to ServerName and ServerAlias directives for the virtual host in the configuration file.
To configure a virtual host, you use the <VirtualHost hostname> container. You must also divide all
served content between the virtual hosts that you configure.
The following example shows a simple name-based configuration for two virtual hosts:
NameVirtualHost *:80
<VirtualHost *:80>
ServerName websvr1.mydom.com
ServerAlias www.mydom-1.com
DocumentRoot /var/www/http/websvr1
ErrorLog websvr1.error_log
</VirtualHost>
<VirtualHost *:80>
ServerName websvr2.mydom.com
ServerAlias www.mydom-2.com
DocumentRoot /var/www/http/sebsvr2
ErrorLog websvr2.error_log
</VirtualHost>
For more information, see http://httpd.apache.org/docs/2.2/vhosts/.
148
Chapter 16 Email Service Configuration
Table of Contents
16.1 About Email Programs ............................................................................................................
16.2 About Email Protocols .............................................................................................................
16.2.1 About SMTP ................................................................................................................
16.2.2 About POP and IMAP ..................................................................................................
16.3 About the Postfix SMTP Server ...............................................................................................
16.4 About the Sendmail SMTP Server ...........................................................................................
16.4.1 About Sendmail Configuration Files ...............................................................................
16.5 Forwarding Email ....................................................................................................................
16.6 Configuring a Sendmail Client .................................................................................................
149
149
149
150
150
151
151
152
152
This chapter describes email programs and protocols that are available with Oracle Linux, and how to set
up a basic Sendmail client.
16.1 About Email Programs
A Mail User Agent is an email client application that allows you to create and read email messages, set up
mailboxes to store and organize messages, and send outbound messages to a Mail Transfer Agent (MTA).
Many MUAs can also retrieve email messages from remote servers using the Post Office Protocol (POP)
or Internet Message Access Protocol (IMAP).
A Mail Transfer Agent (MTA) transports email messages between systems by using the Simple Mail
Transport Protocol (SMTP). The mail delivery services from the client program to a destination server
possibly traverses several MTAs in its route. Oracle Linux offers two MTAs, Postfix and Sendmail, and also
includes the special purpose MTA, Fetchmail for use with SLIP and PPP.
A Mail Delivery Agent (MDA) performs the actual delivery of an email message. The MTA invokes an
MDA, such as Procmail, to place incoming email in the recipient’s mailbox file. MDAs distribute and sort
messages on the local system that email client application can access.
16.2 About Email Protocols
Several different network protocols are required to deliver email messages. These protocols work together
to allow different systems, often running different operating systems and different email programs, to send,
transfer, and receive email.
16.2.1 About SMTP
The Simple Mail Transfer Protocol (SMTP) is a transport protocol that provides mail delivery services
between email client applications and servers, and between the originating server and the destination
server. You must specify the SMTP server when you configure outgoing email for an email client
application.
SMTP does not require authentication. Anyone can use SMTP to send email, including junk email and
unsolicited bulk email. If you administer an SMTP server, you can configure relay restrictions that limit
users from sending email through it. Open relay servers do not have any such restrictions. Both Postfix
and Sendmail are SMTP server programs that use SMTP. Unless you own a domain in which you want to
receive email, you do not need to set up an SMTP server.
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About POP and IMAP
16.2.2 About POP and IMAP
The Post Office Protocol (POP) is an email access protocol that email client applications use to retrieve
email messages from the mailbox on a remote server, typically maintained by an Internet Service Provider
(ISP). POP email clients usually delete the message on the server when it has been successfully retrieved
or within a short time period thereafter.
The Internet Message Access Protocol (IMAP) is an email access protocol that email client applications
use to retrieve email messages from a remote server, typically maintained by their organization. The entire
message is downloaded only when you open it, and you can delete messages from the server without first
downloading them. Email is retained on the server when using IMAP.
Both POP and IMAP allow you to manage mail folders and create multiple mail directories to organize and
store email.
The dovecot package provides the dovecot service that implements both an IMAP server and a POP
server.
By default, the dovecot service runs IMAP and POP together with their secure versions that use Secure
Socket Layer (SSL) encryption for client authentication and data transfer sessions. The IMAP and POP
servers provided by dovecot are configured to work as installed. It is usually unnecessary to modify the
configuration file, /etc/dovecot.conf.
For more information, see the dovecot(1) manual page and /usr/share/doc/dovecot-version.
16.3 About the Postfix SMTP Server
Postfix is configured as the default MTA on Oracle Linux. Although Postfix does not have as many
features as Sendmail, it is easier to administer than Sendmail and its features are sufficient to meet the
requirements of most installations. You should only use Sendmail if you want to use address re-writing
rules or mail filters (milters) that are specific to Sendmail. Most mail filters function correctly with Postfix. If
you do use Sendmail, disable or uninstall Postfix to avoid contention over network port usage.
Postfix has a modular design that consists of a master daemon and several smaller processes. Postfix
stores its configuration files in the /etc/postfix directory, including:
access
Specifies which hosts are allowed to connect to Postfix.
main.cf
Contains global configuration options for Postfix.
master.cf
Specifies how the Postfix master daemon and other Postfix processes interact to deliver
email.
transport
Specifies the mapping between destination email addresses and relay hosts.
By default, Postfix does not accept network connections from any system other than the local host. To
enable mail delivery for other hosts, edit /etc/postfix/main.cf and configure their domain, host
name, and network information.
Restart the Postfix service after making any configuration changes:
# service postfix restart
For more information, see postfix(1) and other Postfix manual pages, Section 16.5, “Forwarding
Email”, /usr/share/doc/postfix-version, and http://www.postfix.org/documentation.html.
150
About the Sendmail SMTP Server
16.4 About the Sendmail SMTP Server
Sendmail is highly configurable and is the most commonly used MTA on the Internet. Sendmail is mainly
used to transfer email between systems, but it is capable of controlling almost every aspect of how email is
handled.
Sendmail is distributed in the following packages:
procmail
Contains Procmail, which acts as the default local MDA for Sendmail. This package is
installed as a dependency of the sendmail package.
sendmail
Contains the Sendmail MTA.
sendmail-cf
Contains configuration files for Sendmail.
To install the Sendmail packages, enter:
# yum install sendmail sendmail-cf
For more information, see the sendmail(8) manual page.
16.4.1 About Sendmail Configuration Files
The main configuration file for Sendmail is /etc/mail/sendmail.cf, which is not intended to be
manually edited. Instead, make any configuration changes in the /etc/mail/sendmail.mc file.
If you want Sendmail to relay email from other systems, change the following line in sendmail.mc:
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
so that it reads:
dnl # DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
The leading dnl stands for delete to new line, and effectively comments out the line.
After you have edited sendmail.mc, restart the sendmail service to regenerate sendmail.cf:
# service sendmail restart
Shutting down sm-client:
Shutting down sendmail:
Starting sendmail:
Starting sm-client:
[
[
[
[
OK
OK
OK
OK
]
]
]
]
Alternatively, you can use the make script in /etc/mail:
# /etc/mail/make all
However, Sendmail does not use the regenerated configuration file until you restart the server.
Other important Sendmail configuration files in /etc/mail include:
access
Configures a relay host that processes outbound mail from the local host to other
systems. This is the default configuration:
Connect: localhost.localdomain
Connect: localhost
Connect: 127.0.0.1
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RELAY
RELAY
RELAY
Forwarding Email
To configure Sendmail to relay mail from other systems on a local network, add an
entry such as the following:
Connect: 192.168.2
RELAY
Configures forwarding of email from one domain to another. The following example
forwards email sent to the yourorg.org domain to the SMTP server for the
mydom.com domain:
mailertable
yourorg.org
virtusertable
smtp:[mydom.com]
Configures serving of email to multiple domains. Each line starts with a destination
address followed by the address to which Sendmail forwards the email. For example,
the following entry forwards email addressed to any user at yourorg.org to the same
user name at mydom.com:
@yourorg.org
[email protected]
Each of these configuration files has a corresponding database (.db) file in /etc/mail that Sendmail
reads. After making any changes to any of the configuration files, restart the sendmail service. To
regenerate the database files, run the /etc/mail/make all command. As for sendmail.cf, Sendmail
does not use the regenerated database files until you restart the server.
16.5 Forwarding Email
You can forward incoming email messages with the Postfix local delivery agent or with Sendmail by
configuring the /etc/aliases file. Entries in this file can map inbound addresses to local users, files,
commands, and remote addresses.
The following example redirects email for postmaster to root, and forwards email sent to admin on the
local system to several other users, including usr04, who is on a different system:
postmaster:
admin:
root
usr01, usr02, usr03, [email protected]
To direct email to a file, specify an absolute path name instead of the destination address. To specify a
command, precede it with a pipe character (|). The next example erases email sent to nemo by sending it
to /dev/null, and runs a script named aggregator to process emails sent to fixme:
nemo:
fixme:
/dev/null
|/usr/local/bin/aggregator
After changing the file, run the command newaliases to rebuild the indexed database file.
For more information, see the aliases(5) manual page.
16.6 Configuring a Sendmail Client
A Sendmail client sends outbound mail to another SMTP server, which is typically administered by an ISP
or the IT department of an organization, and this server then relays the email to its destination.
To configure a Sendmail client:
1. If the account on the SMTP server requires authentication:
a. Create an auth directory under /etc/mail that is accessible only to root:
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Configuring a Sendmail Client
# mkdir /etc/mail/auth
# chmod 700 /etc/mail/auth
b. In the auth directory, create a file smtp-auth that contains the authentication information for the
SMTP server, for example:
# echo 'AuthInfo:smtp.isp.com: "U:username" "P:password"' > /etc/mail/auth/smtp-auth
where smtp.isp.com is the FQDN of the SMTP server, and username and password are the
name and password of the account.
c. Create the database file from smtp-auth, and make both files read-writable only by root:
# cd /etc/mail/auth
# makemap hash smtp-auth < smtp-auth
# chmod 600 smtp-auth smtp-auth.db
2. Edit /etc/mail/sendmail.mc, and change the following line:
dnl define('SMART_host', 'smtp.your.provider')dnl
to read:
define('SMART_host', 'smtp.isp.com')dnl
where smtp.isp.com is the FQDN of the SMTP server.
3. If the account on the SMTP server requires authentication, add the following lines after the line that
defines SMART_host:
define('RELAY_MAILER_ARGS', 'TCP $h port')dnl
define('confAUTH_MECHANISMS', 'EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
FEATURE('authinfo','hash /etc/mail/auth/smtp-auth.db')dnl
define(`confAUTH_OPTIONS', `A p y')dnl
where port is the port number used by the SMTP server (for example, 587 for SMARTTLS or 465 for
SSL/TLS).
4. Edit /etc/sysconfig/sendmail and set the value of DAEMON to no:
DAEMON=no
This entry disables sendmail from listening on port 25 for incoming email.
5. Restart the sendmail service:
# service sendmail restart
To test the configuration, send email to an account in another domain.
This configuration does not receive or relay incoming email. You can use a client application to receive
email via POP or IMAP.
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Part III Storage and File Systems
This section contains the following chapters:
• Chapter 17, Storage Management describes how to configure and manage disk partitions, swap space, logical
volumes, software RAID, block device encryption, iSCSI storage, and multipathing.
• Chapter 18, File System Administration describes how to create, mount, check, and repair file systems, how to
configure Access Control Lists, how to configure and manage disk quotas.
• Chapter 19, Local File System Administration describes administration tasks for the btrfs, ext3, ext4, OCFS2, and
XFS local file systems.
• Chapter 20, Shared File System Administration describes administration tasks for the NFS and Samba shared file
systems, including how to configure NFS and Samba servers.
• Chapter 21, Oracle Cluster File System Version 2 describes how to configure and use the Oracle Cluster File
System Version 2 (OCFS2) file system.
Table of Contents
17 Storage Management .................................................................................................................
17.1 About Disk Partitions .......................................................................................................
17.1.1 Managing Partition Tables Using fdisk ...................................................................
17.1.2 Managing Partition Tables Using parted ................................................................
17.1.3 Mapping Partition Tables to Devices .....................................................................
17.2 About Swap Space .........................................................................................................
17.2.1 Viewing Swap Space Usage .................................................................................
17.2.2 Creating and Using a Swap File ...........................................................................
17.2.3 Creating and Using a Swap Partition .....................................................................
17.2.4 Removing a Swap File or Swap Partition ...............................................................
17.3 About Logical Volume Manager .......................................................................................
17.3.1 Initializing and Managing Physical Volumes ...........................................................
17.3.2 Creating and Managing Volume Groups ................................................................
17.3.3 Creating and Managing Logical Volumes ...............................................................
17.4 About Software RAID ......................................................................................................
17.4.1 Creating Software RAID Devices ...........................................................................
17.5 Creating Encrypted Block Devices ...................................................................................
17.6 About iSCSI Storage .......................................................................................................
17.6.1 Configuring an iSCSI Target .................................................................................
17.6.2 Configuring an iSCSI Initiator ................................................................................
17.6.3 Updating the Discovery Database .........................................................................
17.7 About Device Multipathing ...............................................................................................
17.7.1 Configuring Multipathing .......................................................................................
18 File System Administration .........................................................................................................
18.1 Making File Systems .......................................................................................................
18.2 Mounting File Systems ....................................................................................................
18.2.1 About Mount Options ............................................................................................
18.3 About the File System Mount Table .................................................................................
18.4 Configuring the Automounter ...........................................................................................
18.5 Mounting a File Containing a File System Image ..............................................................
18.6 Creating a File System on a File .....................................................................................
18.7 Checking and Repairing a File System .............................................................................
18.7.1 Changing the Frequency of File System Checking .................................................
18.8 About Access Control Lists ..............................................................................................
18.8.1 Configuring ACL Support ......................................................................................
18.8.2 Setting and Displaying ACLs .................................................................................
18.9 About Disk Quotas ..........................................................................................................
18.9.1 Enabling Disk Quotas on File Systems ..................................................................
18.9.2 Assigning Disk Quotas to Users and Groups .........................................................
18.9.3 Setting the Grace Period ......................................................................................
18.9.4 Displaying Disk Quotas .........................................................................................
18.9.5 Enabling and Disabling Disk Quotas ......................................................................
18.9.6 Reporting on Disk Quota Usage ............................................................................
18.9.7 Maintaining the Accuracy of Disk Quota Reporting .................................................
19 Local File System Administration ................................................................................................
19.1 About Local File Systems ................................................................................................
19.2 About the Btrfs File System .............................................................................................
19.3 Creating a Btrfs File System ............................................................................................
19.4 Modifying a Btrfs File System ..........................................................................................
19.5 Compressing and Defragmenting a Btrfs File System ........................................................
19.6 Resizing a Btrfs File System ............................................................................................
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202
19.7 Creating Subvolumes and Snapshots ............................................................................... 202
19.7.1 Cloning Virtual Machine Images and Linux Containers ........................................... 204
19.8 Using the Send/Receive Feature ..................................................................................... 204
19.8.1 Using Send/Receive to Implement Incremental Backups ......................................... 205
19.9 Using Quota Groups ....................................................................................................... 205
19.10 Replacing Devices on a Live File System ....................................................................... 206
19.11 Creating Snapshots of Files ........................................................................................... 206
19.12 Converting an Ext2, Ext3, or Ext4 File System to a Btrfs File System ............................... 206
19.12.1 Converting a Non-root File System ...................................................................... 207
19.12.2 Converting the root File System .......................................................................... 207
19.12.3 Mounting the Image of the Original File System ................................................... 209
19.12.4 Deleting the Snapshot of the Original File System ................................................ 209
19.12.5 Recovering an Original Non-root File System ....................................................... 209
19.13 Installing a Btrfs root File System ................................................................................... 210
19.13.1 Setting up a New NFS Server ............................................................................. 210
19.13.2 Configuring an Existing NFS Server .................................................................... 211
19.13.3 Setting up a New HTTP Server ........................................................................... 211
19.13.4 Configuring an Existing HTTP Server .................................................................. 212
19.13.5 Setting up a Network Installation Server .............................................................. 213
19.13.6 Installing from a Network Installation Server ......................................................... 214
19.13.7 About the Installation root File System ................................................................. 215
19.13.8 Creating Snapshots of the root File System ......................................................... 216
19.13.9 Mounting Alternate Snapshots as the root File System ......................................... 216
19.13.10 Deleting Snapshots of the root File System ........................................................ 216
19.14 Converting a Non-root Ext2 File System to Ext3 ............................................................. 217
19.15 Converting a root Ext2 File System to Ext3 .................................................................... 217
19.16 Creating a Local OCFS2 File System ............................................................................. 219
19.17 About the XFS File System ........................................................................................... 219
19.17.1 About External XFS Journals .............................................................................. 220
19.17.2 About XFS Write Barriers ................................................................................... 221
19.17.3 About Lazy Counters .......................................................................................... 221
19.18 Installing the XFS Packages .......................................................................................... 221
19.19 Creating an XFS File System ........................................................................................ 221
19.20 Modifying an XFS File System ....................................................................................... 222
19.21 Growing an XFS File System ......................................................................................... 223
19.22 Freezing and Unfreezing an XFS File System ................................................................. 223
19.23 Setting Quotas on an XFS File System .......................................................................... 223
19.23.1 Setting Project Quotas ........................................................................................ 224
19.24 Backing up and Restoring XFS File Systems .................................................................. 225
19.25 Defragmenting an XFS File System ............................................................................... 227
19.26 Checking and Repairing an XFS File System ................................................................. 227
20 Shared File System Administration ............................................................................................. 229
20.1 About Shared File Systems ............................................................................................. 229
20.2 About NFS ...................................................................................................................... 229
20.2.1 Configuring an NFS Server ................................................................................... 231
20.2.2 Mounting an NFS File System .............................................................................. 234
20.3 About Samba .................................................................................................................. 234
20.3.1 Configuring a Samba Server ................................................................................. 234
20.3.2 About Samba Configuration for Windows Workgroups and Domains ........................ 236
20.3.3 Accessing Samba Shares from a Windows Client .................................................. 239
20.3.4 Accessing Samba Shares from an Oracle Linux Client ........................................... 239
21 Oracle Cluster File System Version 2 ......................................................................................... 241
21.1 About OCFS2 ................................................................................................................. 241
21.2 Installing and Configuring OCFS2 .................................................................................... 242
158
21.2.1 Preparing a Cluster for OCFS2 .............................................................................
21.2.2 Configuring the Firewall ........................................................................................
21.2.3 Configuring the Cluster Software ...........................................................................
21.2.4 Creating the Configuration File for the Cluster Stack ..............................................
21.2.5 Configuring the Cluster Stack ...............................................................................
21.2.6 Configuring the Kernel for Cluster Operation ..........................................................
21.2.7 Starting and Stopping the Cluster Stack ................................................................
21.2.8 Creating OCFS2 volumes .....................................................................................
21.2.9 Mounting OCFS2 Volumes ...................................................................................
21.2.10 Querying and Changing Volume Parameters ........................................................
21.3 Troubleshooting OCFS2 ..................................................................................................
21.3.1 Recommended Tools for Debugging .....................................................................
21.3.2 Mounting the debugfs File System ........................................................................
21.3.3 Configuring OCFS2 Tracing ..................................................................................
21.3.4 Debugging File System Locks ...............................................................................
21.3.5 Configuring the Behavior of Fenced Nodes ............................................................
21.4 Use Cases for OCFS2 ....................................................................................................
21.4.1 Load Balancing ....................................................................................................
21.4.2 Oracle Real Application Cluster (RAC) ..................................................................
21.4.3 Oracle Databases .................................................................................................
21.5 For More Information About OCFS2 .................................................................................
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Table of Contents
17.1 About Disk Partitions ...............................................................................................................
17.1.1 Managing Partition Tables Using fdisk ...........................................................................
17.1.2 Managing Partition Tables Using parted ........................................................................
17.1.3 Mapping Partition Tables to Devices .............................................................................
17.2 About Swap Space .................................................................................................................
17.2.1 Viewing Swap Space Usage .........................................................................................
17.2.2 Creating and Using a Swap File ...................................................................................
17.2.3 Creating and Using a Swap Partition .............................................................................
17.2.4 Removing a Swap File or Swap Partition .......................................................................
17.3 About Logical Volume Manager ...............................................................................................
17.3.1 Initializing and Managing Physical Volumes ...................................................................
17.3.2 Creating and Managing Volume Groups ........................................................................
17.3.3 Creating and Managing Logical Volumes .......................................................................
17.4 About Software RAID ..............................................................................................................
17.4.1 Creating Software RAID Devices ..................................................................................
17.5 Creating Encrypted Block Devices ...........................................................................................
17.6 About iSCSI Storage ...............................................................................................................
17.6.1 Configuring an iSCSI Target .........................................................................................
17.6.2 Configuring an iSCSI Initiator ........................................................................................
17.6.3 Updating the Discovery Database .................................................................................
17.7 About Device Multipathing .......................................................................................................
17.7.1 Configuring Multipathing ...............................................................................................
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This chapter describes how to configure and manage disk partitions, swap space, logical volumes,
software RAID, block device encryption, iSCSI storage, and multipathing.
17.1 About Disk Partitions
Partitioning a disk drive divides it into one or more reserved areas (partitions) and stores information about
these partitions in the partition table on the disk The operating system treats each partition as a separate
disk that can contain a file system.
Oracle Linux requires one partition for the root file system. It is usual to use two other partitions for swap
space and the boot file system. On x86 and x86_64 systems, the system BIOS can usually access only
the first 1024 cylinders of the disk at boot time. Configuring a separate boot partition in this region on the
disk allows the GRUB bootloader to access the kernel image and other files that are required to boot the
system.
You can create additional partitions to simplify backups, to enhance system security, and to meet other
needs, such as setting up development sandboxes and test areas. Data that frequently changes, such as
user home directories, databases, and log file directories, is typically assigned to separate partitions to
facilitate backups.
The partitioning scheme for hard disks with a master boot record (MBR) allows you to create up to four
primary partitions. If you need more than four partitions, you can divide one of the primary partitions into
up to 11 logical partitions. The primary partition that contains the logical partitions is known as an extended
partition. The MBR scheme supports disks up to 2 TB in size.
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Managing Partition Tables Using fdisk
On hard disks with a GUID Partition Table (GPT), you can configure up to 128 partitions and there is no
concept of extended or logical partitions. You should configure a GPT if the disk is larger than 2 TB.
You can create and manage MBRs by using the fdisk command. If you want to create a GPT, use
parted instead.
17.1.1 Managing Partition Tables Using fdisk
Caution
If any partition on the disk to be configured using fdisk is currently mounted,
unmount it before running fdisk on the disk. Similarly, if any partition is being used
as swap space, use the swapoff command to disable the partition.
Before running fdisk on a disk that contains data, first back up the data on to
another disk or medium.
You cannot use fdisk to manage a GPT hard disk.
You can use the fdisk utility to create a partition table, view an existing partition table, add partitions, and
delete partitions. Alternatively, you can also use the cfdisk utility, which is a text-based, graphical version
of fdisk.
You can use fdisk interactively or you can use command-line options and arguments to specify partitions.
When you run fdisk interactively, you specify only the name of the disk device as an argument, for
example:
# fdisk /dev/sda
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').
Command (m for help):
Enter c to switch off DOS-compatibility mode, and p to display the partition table:
Command (m for help): c
DOS Compatibility flag is not set
Command (m for help): p
Disk /dev/sda: 42.9 GB, 42949672960 bytes
255 heads, 63 sectors/track, 5221 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0002a95d
Device Boot
/dev/sda1
*
/dev/sda2
Start
1
64
End
64
5222
Blocks
512000
41430016
Id
83
8e
System
Linux
Linux LVM
The example output shows that /dev/sda is a 42.9 GB disk. As modern hard disks support logical block
addressing (LBA), any information about the numbers of heads and sectors per track is irrelevant and
probably fictitious. The cylinder size is used as the unit for the start and end offsets of each partition from
the beginning of the disk. The partition table is displayed after the device summary, and shows:
Device
The device that corresponds to the partition.
Boot
Specifies * if the partition contains the files that the GRUB bootloader needs to boot
the system. Only one partition can be bootable.
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Managing Partition Tables Using fdisk
Start and End
The start and end offsets in cylinders. All partitions are aligned on cylinder boundaries.
Blocks
The size of the partition in 1-kilobyte blocks.
Id and System
The partition type. The following partition types are typically used with Oracle Linux:
5 Extended
An extended partition that can contain up to four logical partitions.
82 Linux swap
Swap space partition.
83 Linux
Linux partition for a file system that is not managed by LVM. This is
the default partition type.
8e Linux LVM
Linux partition that is managed by LVM.
The n command creates a new partition. For example, to create partition table entries for two Linux
partitions on /dev/sdc, one of which is 5 GB in size and the other occupies the remainder of the disk:
# fdisk /dev/sdc
...
Command (m for help): n
Command action
e
extended
p
primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-1958, default 1): 1
Last cylinder, +cylinders or +size{K,M,G} (1-1958, default 1958): +5G
Command (m for help): n
Command action
e
extended
p
primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (655-1958, default 655): <Enter>
Using default value 655
Last cylinder, +cylinders or +size{K,M,G} (1-1958, default 1958): <Enter>
Using default value 1958
Command (m for help): p
Device Boot
Start
/dev/sdc1
1
/dev/sdc2
655
End
654
1958
Blocks
Id System
5253223+ 83 Linux
10474380 83 Linux
The t command allows you to change the type of a partition. For example, to change the partition type of
partition 2 to Linux LVM:
Command (m for help): t
Partition number (1-4): 2
Hex code (type L to list codes): 8e
Command (m for help): p
Device Boot
Start
/dev/sdc1
1
/dev/sdc2
655
End
654
1958
Blocks
Id System
5253223+ 83 Linux
10474380 8e Linux LVM
After creating the new partition table, use the w command to write the table to the disk and exit fdisk.
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
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Managing Partition Tables Using parted
If you enter q instead, fdisk exits without committing the changes to disk.
For more information, see the cfdisk(8) and fdisk(8) manual pages.
17.1.2 Managing Partition Tables Using parted
Caution
If any partition on the disk to be configured using parted is currently mounted,
unmount it before running parted on the disk. Similarly, if any partition is being
used as swap space, use the swapoff command to disable the partition.
Before running parted on a disk that contains data, first back up the data on to
another disk or medium.
You can use the parted utility to label a disk, create a partition table, view an existing partition table, add
partitions, change the size of partitions, and delete partitions. parted is more advanced than fdisk as it
supports more disk label types, including GPT disks, and it implements a larger set of commands.
You can use parted interactively or you can specify commands as arguments. When you run parted
interactively, you specify only the name of the disk device as an argument, for example:
# parted /dev/sda
GNU Parted 2.1
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted)
The print command displays the partition table:
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sda: 42.9GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number
1
2
Start
1049kB
525MB
End
525MB
42.9GB
Size
524MB
42.4GB
Type
primary
primary
File system
ext4
Flags
boot
lvm
The mklabel command creates a new partition table:
# parted /dev/sdd
GNU Parted 2.1
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) mklabel
New disk label type? gpt
Warning: The existing disk label on /dev/sdd will be destroyed
and all data on this disk will be lost. Do you want to continue?
Yes/No? y
Typically, you would set the disk label type to gpt or msdos for an Oracle Linux system, depending on
whether the disk device supports GPT. You are prompted to confirm that you want to overwrite the existing
disk label.
The mkpart command creates a new partition:
(parted) mkpart
Partition name? []? <Enter>
File system type? [ext2]? ext4
Start? 1
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Mapping Partition Tables to Devices
End? 5GB
For disks with an msdos label, you are also prompted to enter the partition type, which can be primary,
extended, or logical. The file system type is typically set to one of fat16, fat32, ext4, or linuxswap for an Oracle Linux system. If you are going to create an btrfs, ext*, ocfs2, or xfs file system on
the partition, specify ext4. Unless you specify units such as GB for gigabytes, the start and end offsets of
a partition are assumed to be in megabytes.
To display the new partition, enter the print command:
(parted) print
Number
Start
1
1049kB
End
5000MB
Size
4999MB
File system
ext4
Name
Flags
To exit parted, enter quit.
Note
parted commands such as mklabel and mkpart commit the changes to disk
immediately. Unlike fdisk, you do not have the option of quitting without saving
your changes.
For more information, see the parted(8) manual page or enter info parted to view the online user
manual.
17.1.3 Mapping Partition Tables to Devices
You can use the kpartx utility to map the partitions of any block device or file that contains a partition
table and partition images. kpartx reads the partition table and creates device files for the partitions in /
dev/mapper. Each device file represents a disk volume or a disk partition on a device or within an image
file.
The -l option lists any partitions that it finds, for example in an installation image file:
# kpartx –l
loop0p1 : 0
loop0p2 : 0
loop0p3 : 0
loop0p4 : 0
system.img
204800 /dev/loop0 2048
12288000 /dev/loop0 206848
4096000 /dev/loop0 212494848
2 /dev/loop0 16590848
This output shows that the drive image contains four partitions, and the first column are the names of the
device files that can be created in /dev/mapper.
The -a option creates the device mappings:
# kpartx –a system.img
# ls /dev/mapper
control loop0p1 loop0p2
loop0p3
loop0p4
If a partition contains a file system, you can mount it and view the files that it contains, for example:
# mkdir /mnt/sysimage
# mount /dev/mapper/loop0p1 /mnt/sysimage
# ls /mnt/sysimage
config-2.6.32-220.el6.x86_64
config-2.6.32-300.3.1.el6uek.x86_64
efi
grub
initramfs-2.6.32-220.el6.x86_64.img
initramfs-2.6.32-300.3.1.el6uek.x86_64.img
...
# umount /mnt/sysimage
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About Swap Space
The -d option removes the device mappings:
# kpartx –d system.img
# ls /dev/mapper
control
For more information, see the kpartx(8) manual page.
17.2 About Swap Space
Oracle Linux uses swap space when your system does not have enough physical memory to store the text
(code) and data pages that the processes are currently using. When your system needs more memory, it
writes inactive pages to swap space on disk, freeing up physical memory. However, writing to swap space
has a negative impact on system performance, so increasing swap space is not an effective solution to
shortage of memory. Swap space is located on disk drives, which have much slower access times than
physical memory. If your system often resorts to swapping, you should add more physical memory, not
more swap space.
You can configure swap space on a swap file in a file system or on a separate swap partition. A dedicated
swap partition is faster, but changing the size of a swap file is easier. Configure a swap partition if you
know how much swap space your system requires. Otherwise, start with a swap file and create a swap
partition when you know what your system requires.
17.2.1 Viewing Swap Space Usage
To view a system's usage of swap space, examine the contents of /proc/swaps:
# cat /proc/swaps
Filename
/dev/sda2
/swapfile
Type
partition
file
Size
4128760
999992
Used
388
0
Priority
-1
-2
In this example, the system is using both a 4-gigabyte swap partition on /dev/sda2 and a 1-gigabyte
swap file, /swapfile. The Priority column shows that the system preferentially swaps to the swap
partition rather than to the swap file.
You can also view /proc/meminfo or use utilities such as free, top, and vmstat to view swap space
usage, for example:
# grep Swap /proc/meminfo
SwapCached:
248 kB
SwapTotal:
5128752 kB
SwapFree:
5128364 kB
# free | grep Swap
Swap:
5128752
388
5128364
17.2.2 Creating and Using a Swap File
To create and use a swap file:
1. Use the dd command to create a file of the required size (for example, one million 1-kilobyte blocks):
# dd if=/dev/zero of=/swapfile bs=1024 count=1000000
2. Initialize the file as a swap file:
# mkswap /swapfile
3. Enable swapping to the swap file:
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Creating and Using a Swap Partition
# swapon /swapfile
4. Add an entry to /etc/fstab for the swap file so that the system uses it following the next reboot:
/swapfile
swap
swap
defaults
0 0
17.2.3 Creating and Using a Swap Partition
To create and use a swap partition:
1. Use fdisk to create a disk partition of type 82 (Linux swap) or parted to create a disk partition of
type linux-swap of the size that you require.
2. Initialize the partition (for example, /dev/sda2) as a swap partition:
# mkswap /dev/sda2
3. Enable swapping to the swap partition:
# swapon /swapfile
4. Add an entry to /etc/fstab for the swap partition so that the system uses it following the next reboot:
/dev/sda2
swap
swap
defaults
0 0
17.2.4 Removing a Swap File or Swap Partition
To remove a swap file or swap partition from use:
1. Disable swapping to the swap file or swap partition, for example:
# swapoff /swapfile
2. Remove the entry for the swap file or swap partition from /etc/fstab.
3. Optionally, remove the swap file or swap partition if you do not want to use it in future.
17.3 About Logical Volume Manager
You can use Logical Volume Manager (LVM) to manage multiple physical volumes and configure mirroring
and striping of logical volumes to provide data redundancy and increase I/O performance. In LVM, you
first create volume groups from physical volumes, which are storage devices such as disk array LUNs,
software or hardware RAID devices, hard drives, and disk partitions. You can then create logical volumes
in a volume group. A logical volume functions as a partition that in its implementation might be spread over
multiple physical disks.
You can create file systems on logical volumes and mount the logical volume devices in the same way as
you would a physical device. If a file system on a logical volume becomes full with data, you can increase
the capacity of the volume by using free space in the volume group so that you can then grow the file
system (provided that the file system has that capability). If necessary, you can add physical storage
devices to a volume group to increase its capacity.
LVM is non-disruptive and transparent to users. You can increase the size of logical volumes and change
their layout dynamically without needing to schedule system down time to reconfigure physical storage.
LVM uses the device mapper (DM) that provides an abstraction layer that allows the creation of logical
devices above physical devices and provides the foundation for software RAID, encryption, and other
storage features.
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Initializing and Managing Physical Volumes
17.3.1 Initializing and Managing Physical Volumes
Before you can create a volume group, you must initialize the physical devices that you want to use as
physical volumes with LVM.
Caution
If the devices contain any existing data, back up the data.
To set up a physical device as a physical volume, use the pvcreate command:
# pvcreate [options] device ...
For example, set up /dev/sdb, /dev/sdc, /dev/sdd, and /dev/sde as physical volumes:
# pvcreate -v /dev/sd[bcde]
Set up physical volume for “/dev/sdb” with 6313482 available
sectors
Zeroing start of device /dev/sdb
Physical volume “/dev/sdb” successfully created
...
To display information about physical volumes, you can use the pvdisplay, pvs, and pvscan
commands.
To remove a physical volume from the control of LVM, use the pvremove command:
# pvremove device
Other commands that are available for managing physical volumes include pvchange, pvck, pvmove,
and pvresize.
For more information, see the lvm(8), pvcreate(8), and other LVM manual pages.
17.3.2 Creating and Managing Volume Groups
Having initialized the physical volumes, you can add them to a new or existing volume group.
To create a volume group, use the vgcreate command:
# vgcreate [options] volume_group physical_volume ...
For example, create the volume group myvg from the physical volumes /dev/sdb, /dev/sdc, /dev/
sdd, and /dev/sde:
# vgcreate -v myvg /dev/sd[bcde]
Wiping cache of LVM-capable devices
Adding physical volume ‘/dev/sdb’ to volume group ‘myvg’
Adding physical volume ‘/dev/sdc’ to volume group ‘myvg’
Adding physical volume ‘/dev/sdd’ to volume group ‘myvg’
Adding physical volume ‘/dev/sde’ to volume group ‘myvg’
Archiving volume group “myvg” metadata (seqno 0).
Creating volume group backup “/etc/lvm/backup/myvg” (seqno 1).
Volume group “myvg” successfully created
LVM divides the storage space within a volume group into physical extents, which are the smallest unit that
LVM uses when allocating storage to logical volumes. The default size of an extent is 4 MB.
The allocation policy for the volume group and logical volume determines how LVM allocates extents from
a volume group. The default allocation policy for a volume group is normal, which applies rules such as
not placing parallel stripes on the same physical volume. The default allocation policy for a logical volume
is inherit, which means that the logical volume uses the same policy as for the volume group. You
168
Creating and Managing Logical Volumes
can change the default allocation policies by using the lvchange or vgchange commands, or you can
override the allocation policy when you create a volume group or logical volume. Other allocation policies
include anywhere, contiguous and cling.
To add physical volumes to a volume group, use the vgextend command:
# vgextend [options] volume_group physical_volume ...
To remove physical volumes from a volume group, use the vgreduce command:
# vgreduce [options] volume_group physical_volume ...
To display information about volume groups, you can use the vgdisplay, vgs, and vgscan commands.
To remove a volume group from LVM, use the vgremove command:
# vgremove volume_group
Other commands that are available for managing volume groups include vgchange, vgck, vgexport,
vgimport, vgmerge, vgrename, and vgsplit.
For more information, see the lvm(8), vgcreate(8), and other LVM manual pages.
17.3.3 Creating and Managing Logical Volumes
Having create a volume group of physical volumes, you can create logical volumes from the storage space
that is available in the volume group.
To create a logical volume, use the lvcreate command:
# lvcreate [options] --size size --name logical_volume volume_group
For example, create the logical volume mylv of size 2 GB in the volume group myvg:
# lvcreate -v --size 2g --name mylv myvg
Setting logging type to disk
Finding volume group “myvg”
Archiving volume group “myvg” metadata (seqno 1).
Creating logical volume mylv
Create volume group backup “/etc/lvm/backup/myvg” (seqno 2).
...
lvcreate uses the device mapper to create a block device file entry under /dev for each logical volume
and uses udev to set up symbolic links to this device file from /dev/mapper and /dev/volume_group.
For example, the device that corresponds to the logical volume mylv in the volume group myvg might be /
dev/dm-3, which is symbolically linked by /dev/mapper/myvolg-myvol and /dev/myvolg/myvol.
Note
Always use the devices in /dev/mapper or /dev/volume_group. These names
are persistent and are created automatically by the device mapper early in the
boot process. The /dev/dm-* devices are not guaranteed to be persistent across
reboots.
Having created a logical volume, you can configure and use it in the same way as you would a physical
storage device. For example, you can configure a logical volume as a file system, swap partition,
Automatic Storage Management (ASM) disk, or raw device.
You can also use lvcreate to create a snapshot of an existing logical volume such as mylv in the
volume group myvg, for example:
# lvcreate --size 500m –-snapshot –-name mylv-snapshot myvg/mylv
169
About Software RAID
Logical volume “mylv-snapshot” created
You can mount and modify the contents of the snapshot independently of the original volume or preserve it
as a record of the state of the original volume at the time that you took the snapshot. The snapshot usually
takes up less space than the original volume, depending on how much the contents of the volumes diverge
over time. In the example, we assume that the snapshot only requires one quarter of the space of the
original volume. You can use the value shown by the Snap% column in the output from the lvs command
to see how much data is allocated to the snapshot. If the value of Snap% approaches 100%, indicating that
a snapshot is running out of storage, use lvresize to grow it. Alternatively, you can reduce a snapshot's
size to save storage space. To merge a snapshot with its original volume, use the lvconvert command,
specifying the --merge option.
To display information about logical volumes, you can use the lvdisplay, lvs, and lvscan commands.
To remove a logical volume from a volume group, use the lvremove command:
# lvremove volume_group/logical_volume
Note
You must specify both the name of the volume group and the logical volume.
Other commands that are available for managing logical volumes include lvchange, lvconvert,
lvmdiskscan, lvmsadc, lvmsar, lvrename, and lvresize.
For more information, see the lvm(8), lvcreate(8), and other LVM manual pages.
17.4 About Software RAID
The Redundant Array of Independent Disks (RAID) feature allows you to spread data across the drives to
increase capacity, implement data redundancy, and increase performance. RAID is usually implemented
either in hardware on intelligent disk storage that exports the RAID volumes as LUNs, or in software by the
operating system. Oracle Linux kernel uses the multidisk (MD) driver to support software RAID by creating
virtual devices from two or more physical storage devices. You can use MD to organize disk drives into
RAID devices and implement different RAID levels.
The following software RAID levels are commonly used with Oracle Linux:
Linear RAID (spanning)
Combines drives as a larger virtual drive. There is no data redundancy
or performance benefit. Resilience decreases because the failure of a
single drive renders the array unusable.
RAID-0 (striping)
Increases performance but does not provide data redundancy. Data is
broken down into units (stripes) and written to all the drives in the array.
Resilience decreases because the failure of a single drive renders the
array unusable.
RAID-1 (mirroring)
Provides data redundancy and resilience by writing identical data
to each drive in the array. If one drive fails, a mirror can satisfy I/
O requests. Mirroring is an expensive solution because the same
information is written to all of the disks in the array.
RAID-5 (striping with distributed
parity)
Increases read performance by using striping and provides data
redundancy. The parity is distributed across all the drives in an array
but it does not take up as much space as a complete mirror. Write
performance is reduced to some extent from RAID-0 by having to
calculate parity information and write this information in addition to
170
Creating Software RAID Devices
the data. If one disk in the array fails, the parity information is used to
reconstruct data to satisfy I/O requests. In this mode, read performance
and resilience are degraded until you replace the failed drive and it is
repopulated with data and parity information. RAID-5 is intermediate in
expense between RAID-0 and RAID-1.
RAID-6 (striping with double
distributed parity)
A more resilient variant of RAID-5 that can recover from the loss of
two drives in an array. RAID-6 is used when data redundancy and
resilience are important, but performance is not. RAID-6 is intermediate
in expense between RAID-5 and RAID-1.
RAID 0+1 (mirroring of striped
disks)
Combines RAID-0 and RAID-1 by mirroring a striped array to provide
both increased performance and data redundancy. Failure of a single
disk causes one of the mirrors to be unusable until you replace the disk
and repopulate it with data. Resilience is degraded while only a single
mirror remains available. RAID 0+1 is usually as expensive as or slightly
more expensive than RAID-1.
RAID 1+0 (striping of mirrored
disks or RAID-10)
Combines RAID-0 and RAID-1 by striping a mirrored array to provide
both increased performance and data redundancy. Failure of a single
disk causes part of one mirror to be unusable until you replace the
disk and repopulate it with data. Resilience is degraded while only a
single mirror retains a complete copy of the data. RAID 1+0 is usually as
expensive as or slightly more expensive than RAID-1.
17.4.1 Creating Software RAID Devices
To create a software RAID device:
1. Use the mdadm command to create the MD RAID device:
# mdadm --create md_device --level=RAID_level [options] --raid-devices=N device ...
For example, to create a RAID-1 device /dev/md0 from /dev/sdf and /dev/sdg:
# mdadm --create /dev/md0 --level=1 –raid-devices=2 /dev/sd[fg]
Create a RAID-5 device /dev/md1 from /dev/sdb, /dev/sdc, and dev/sdd:
# mdadm --create /dev/md1 --level=5 –raid-devices=3 /dev/sd[bcd]
If you want to include spare devices that are available for expansion, reconfiguration, or replacing failed
drives, use the --spare-devices option to specify their number, for example:
# mdadm --create /dev/md1 --level=5 –raid-devices=3 --spare-devices=1 /dev/sd[bcde]
Note
The number of RAID and spare devices must equal the number of devices that
you specify.
2. Add the RAID configuration to /etc/mdadm.conf:
# mdadm --examine --scan >> /etc/mdadm.conf
Note
This step is optional. It helps mdadm to assemble the arrays at boot time.
171
Creating Encrypted Block Devices
For example, the following entries in /etc/mdadm.conf define the devices and arrays that
correspond to /dev/md0 and /dev/md1:
DEVICE /dev/sd[c-g]
ARRAY /dev/md0 devices=/dev/sdf,/dev/sdg
ARRAY /dev/md1 spares=1 devices=/dev/sdb,/dev/sdc,/dev/sdd,/dev/sde
For more examples, see the sample configuration file /usr/share/doc/mdadm-3.2.1/
mdadm.conf-example.
Having created an MD RAID device, you can configure and use it in the same way as you would a physical
storage device. For example, you can configure it as an LVM physical volume, file system, swap partition,
Automatic Storage Management (ASM) disk, or raw device.
You can view /proc/mdstat to check the status of the MD RAID devices, for example:
# cat /proc/mdstat
Personalities : [raid1]
mdo : active raid1 sdg[1] sdf[0]
To display summary and detailed information about MD RAID devices, you can use the --query and -detail options with mdadm.
For more information, see the md(4), mdadm(8), and mdadm.conf(5) manual pages.
17.5 Creating Encrypted Block Devices
The device mapper supports the creation of encrypted block devices using the dm-crypt device driver.
You can access data on encrypted devices at boot time only if you enter the correct password. As the
underlying block device is encrypted and not the file system, you can use dm-crypt to encrypt disk
partitions, RAID volumes, and LVM physical volumes, regardless of their contents.
When you install Oracle Linux, you have the option of configure encryption on system volumes other than
the partition from which the system boots. If you want to protect the bootable partition, consider using any
password protection mechanism that is built into the BIOS or setting up a GRUB password.
You use the cryptsetup utility to set up Linux Unified Key Setup (LUKS) encryption on the device and to
manage authentication.
To set up the mapped device for an encrypted volume:
1. Initialize a LUKS partition on the device and set up the initial key, for example:
# cryptsetup luksFormat /dev/sdd
WARNING!
========
This will overwrite data on /dev/sdd irrevocably.
Are you sure? (Type uppercase yes): YES
Enter LUKS passphrase: passphrase
Verify passphrase: passphrase
2. Open the device and create the device mapping:
# cryptsetup luksOpen /dev/sdd cryptfs
Enter passphrase for /dev/sdd: passphrase
In this example, the encrypted volume is accessible as /dev/mapper/cryptsfs.
3. Create an entry for the encrypted volume in /etc/crypttab, for example:
172
About iSCSI Storage
# <target name>
cryptfs
<source device>
/dev/sdd
<key file>
none
<options>
luks
This entry causes the operating system to prompt you to enter the passphrase at boot time.
Having created an encrypted volume and its device mapping, you can configure and use it in the same way
as you would a physical storage device. For example, you can configure it as an LVM physical volume,
file system, swap partition, Automatic Storage Management (ASM) disk, or raw device. For example, you
would create an entry in the /etc/fstab to mount the mapped device (/dev/mapper/cryptsfs), not
the physical device (/dev/sdd).
To verify the status of an encrypted volume, use the following command:
# cryptsetup status cryptfs
/dev/mapper/cryptfs is active.
type: LUKS1
cipher: aes-cbs-essiv:sha256
keysize: 256 bits
device: /dev/xvdd1
offset: 4096 sectors
size:
6309386 sectors
mode:
read/write
Should you need to remove the device mapping, unmount any file system that the encrypted volume
contains, and run the following command:
# cryptsetup luksClose /dev/mapper/cryptfs
For more information, see the crypsetup(8) and crypttab(5) manual pages.
17.6 About iSCSI Storage
The Internet Small Computer System Interface (iSCSI) is an IP-based standard for connecting storage
devices. iSCSI encapsulates SCSI commands in IP network packets, which allows data transfer over long
distances and sharing of storage by client systems. As iSCSI uses the existing IP infrastructure, it does
not require the purchase and installation of fiber-optic cabling and interface adapters that are needed to
implement Fibre Channel (FC) storage area networks.
A client system (iSCSI initiator) accesses the storage server (iSCSI target) over an IP network. To an
iSCSI initiator, the storage appears to be locally attached.
Figure 17.1 shows a simple network where several iSCSI initiators are able to access the shared storage
that is attached to an iSCSI target.
Figure 17.1 iSCSI Initiators and an iSCSI Target Connected via an IP-based Network
173
Configuring an iSCSI Target
A hardware-based iSCSI initiator uses a dedicated iSCSI HBA. Oracle Linux supports iSCSI initiator
functionality in software. The kernel-resident device driver uses the existing network interface card (NIC)
and network stack to emulate a hardware iSCSI initiator. As the iSCSI initiator functionality is not available
at the level of the system BIOS, you cannot boot an Oracle Linux system from iSCSI storage .
To improve performance, some network cards implement TCP/IP Offload Engines (TOE) that can create a
TCP frame for the iSCSI packet in hardware. Oracle Linux does not support TOE, although suitable drivers
may be available directly from the card vendor.
17.6.1 Configuring an iSCSI Target
An iSCSI target is typically a dedicated, network-connected storage device but it can also be a generalpurpose computer. The procedure in this section demonstrates how to set up a simple iSCSI target.
To configure an Oracle Linux system as an iSCSI target:
1. Install the scsi-target-utils package:
# yum install scsi-target-utils
2. Edit /etc/tgt/targets.conf and create entries for the iSCSI target and the storage devices
(LUNs) that it will make available, for example:
<target iqn.2012-01.com.mydom.host01:target1>
direct-store /dev/sdb # LUN 1
direct-store /dev/sdc # LUN 2
</target>
The /etc/tgt/targets.conf file contains several sample configurations that you can use as
templates.
In the example, the target is uniquely identified by its iSCSI Qualified Name (IQN), which takes the
format:
iqn.YYYY-MM.reverse_FQDN[:target_name]
where:
YYYY-MM
Specifies the year and month that the naming authority took ownership of the
domain.
reverse_FQDN
Specifies the reverse fully qualified domain name of the naming authority.
target_name
Specifies an optional target name, which identifies the target at a site.
3. Start the iSCSI target service, tgtd, and configure it to start after the system reboots:
# service tgtd start
# chkconfig tgtd on
4. Use the tgtadm command to verify that the iSCSI target is available:
# tgtadm -o show -m target
Target 1: iqn.2012-01.com.mydom.host01:target1
System information:
Driver: iscsi
State: ready
I_T nexus information:
LUN information:
LUN: 0
174
Configuring an iSCSI Initiator
Type: controller
SCSI ID: deadbeaf1:0
SCSI SN: beaf10
Size: 0 MB
Online: Yes
Removable media: No
Backing store: No backing store
LUN: 1
Type: disk
SCSI ID: deadbeaf1:1
SCSI SN: beaf11
Size: 10737 MB
Online: Yes
Removable media: No
Backing store: No
...
You can use the tgtadm utility to monitor and configure iSCSI targets. In addition, the tgt-admin script
provides a simplifed interface to the tgtadm commands that create, delete, and show target information.
The tgt-setup-lun script allows you to create targets, add devices to targets, and define which iSCSI
initiators are allowed to connect to a target.
For more information, see the targets.conf(5), tgt-admin(8), tgt-setup-lun(8), and
tgtadm(8) manual pages.
17.6.2 Configuring an iSCSI Initiator
To configure an Oracle Linux system as an iSCSI initiator:
1. Install the iscsi-initiator-utils package:
# yum install iscsi-initiator-utils
2. Use the SendTargets discovery method to discover the iSCSI targets at a specified IP address:
# iscsiadm -m discovery --type sendtargets –p 10.150.30.72
Starting iscsid:
[ OK ]
10.150.30.72:3260,1 iqn.2012-01.com.mydom.host01:target1
10.150.30.72:3260,1 iqn.2012-01.com.mydom.host01:target2
Note
An alternate discovery method is Internet Storage Name Service (iSNS).
The command also starts the iscsid service if it is not already running.
The following command displays information about the targets that is now stored in the discovery
database:
# iscsiadm -m discoverydb –t st –p 10.150.30.72
# BEGIN RECORD 2.0-872.41.el6
discovery.startup = manual
discovery.type = sendtargets
discovery.sendtargets.address = 10.150.30.72
discovery.sendtargets.port = 3260
discovery.sendtargets.auth.authmethod = None
discovery.sendtargets.auth.username_in = <empty>
discovery.sendtargets.auth.password_in = <empty>
discovery.sendtargets.timeo.login_timeout = 15
discovery.sendtargets.use_discoveryd = No
discovery.sendtargets.discoveryd_poll_inval = 30
discovery.sendtargets.repoen_max = 5
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Configuring an iSCSI Initiator
discovery.sendtargets.timeo.auth_timeout = 45
discovery.sendtargets.timeo.active_timeout = 30
discovery.sendtargets.iscsi.MaxRecvDataSegmentLength = 32768
3. Establish a session and log in to a specific target:
# iscsiadm -m node --targetname iqn.2012-01.com.mydom.host01:target1 \
–p 10.150.30.72:3260 -l
Login to [iface: default, target: iqn.2012-01.com.mydom.host01:target1,
portal: 10.150.30.72:3260] successful.
4. Verify that the session is active, and display the available LUNs:
# iscsiadm -m session –P 3
Target: iqn.2012-01.com.mydom.host01:target1
Current Portal: 10.150.30.72:3260,1
Persistent Portal: 10.150.30.72:3260,1
**********
Interface:
**********
Iface Name: default
Iface Transport: tcp
Iface Initiatorname: iqn.1988-12.com.mydom:392a7cee2f
Iface IPaddress: 192.0.2.101
Iface HWaddress: <empty>
Iface Netdev: <empty>
SID: 1
iSCSI Connection State: LOGGED IN
iSCSI Session State: LOGGED IN
Internal iscsid Session State: NO CHANGE
.
.
.
************************
Attached SCSI devices:
************************
Host Number: 4 State: running
scsi10 Channel 00 Id 0 Lun:0
scsi10 Channel 00 Id 0 Lun:1
Attached scsi disk sdb
State: running
scsi10 Channel 00 Id 0 Lun:2
Attached scsi disk sdc
State: running
The LUNs are represented as SCSI block devices (sd*) in the local /dev directory, for example:
# fdisk –l | grep /dev/sd[bc]
Disk /dev/sdb: 10.7 GB, 10737418240 bytes
Disk /dev/sdc: 10.7 GB, 10737418240 bytes
To distinguish between target LUNs, examine their paths under /dev/disk/by-path:
# ls -l /dev/disk/by-path/
lrwxrwxrwx 1 root root 9 May 15 21:05
ip-10.150.30.72:3260-iscsi-iqn.2012-01.com.mydom.host01:02:
084591f8-6b8b-c857-f002-ecf8a3b387f3-lun-1 -> ../../sdb
lrwxrwxrwx 1 root root 9 May 15 21:05
ip-10.150.30.72:3260-iscsi-iqn.2012-01.com.mydom.host01:02:
084591f8-6b8b-c857-f002-ecf8a3b387f3-lun-2 -> ../../sdc
You can view the initialization messages for the LUNs in the /var/log/messages file:
# grep -i scsi /var/log/messages
Apr 8 15:08:53 host02 kernel: scsi12 : iSCSI Initiator over TCP/IP
Apr 8 15:08:53 host02 kernel: sd 4:0:0:1: [sdb] Attached SCSI disk
176
Updating the Discovery Database
Apr 8 15:08:53 host02 kernel: sd 4:0:0:2: [sdc] Attached SCSI disk
You can configure and use a LUN in the same way as you would any other physical storage device.
For example, you can configure it as an LVM physical volume, file system, swap partition, Automatic
Storage Management (ASM) disk, or raw device.
Specify the _netdev option when creating mount entries for iSCSI LUNs in /etc/fstab, for example:
UUID=084591f8-6b8b-c857-f002-ecf8a3b387f3
/iscsi_mount_point
ext4
_netdev
0
0
This option indicates the file system resides on a device that requires network access, and prevents the
system from attempting to mount the file system until the network has been enabled.
Note
Specify an iSCSI LUN in /etc/fstab by using UUID=UUID rather than the
device path. A device path can change after re-connecting the storage or
rebooting the system. You can use the blkid command to display the UUID of
a block device.
Any discovered LUNs remain available across reboots provided that the target
continues to serve those LUNs and you do not log the system off the target.
For more information, see the iscsiadm(8) and iscsid(8) manual pages.
17.6.3 Updating the Discovery Database
If the LUNs that are available on an iSCSI target change, you can use the iscsiadm command on an
iSCSI initiator to update the entries in its discovery database. The following example assume that the
target supports the SendTargets discovery method
To add new records that are not currently in the database:
# iscsiadm -m discoverydb –t st –p 10.150.30.72 –o new --discover
To update existing records in the database:
# iscsiadm -m discoverydb –t st –p 10.150.30.72 –o update --discover
To delete records from the database that are no longer supported by the target:
# iscsiadm -m discoverydb –t st –p 10.150.30.72 –o delete --discover
For more information, see the iscsiadm(8) manual page.
17.7 About Device Multipathing
Multiple paths to storage devices can provide connection redundancy, failover capability, load balancing,
and improved performance. Device-Mapper Multipath (DM-Multipath) is a multipathing tool that allows you
to represent multiple I/O paths between a server and a storage device as a single path.
You would be most likely to configure multipathing with a system that can access storage on a Fibre
Channel-based storage area network (SAN). You can also use multipathing on an iSCSI initiator if
redundant network connections exist between the initiator and the target. However, Oracle VM does not
support multipathing over iSCSI.
Figure 17.2 shows a simple DM-Multipath configuration where two I/O paths are configured between a
server and a disk on a SAN-attached storage array:
177
Configuring Multipathing
• Between host bus adapter hba1 on the server and controller ctrl1 on the storage array.
• Between host bus adapter hba2 on the server and controller ctrl2 on the storage array.
Figure 17.2 DM-Multipath Mapping of Two Paths to a Disk over a SAN
Without DM-Multipath, the system treats each path as being separate even though it connects the server
to the same storage device. DM-Multipath creates a single multipath device, /dev/mapper/mpathN, that
subsumes the underlying devices, /dev/sdc and /dev/sdf.
You can configure the multipathing service (multipathd) to handle I/O from and to a multipathed device
in one of the following ways:
Active/Active
I/O is distributed across all available paths, either by round-robin
assignment or dynamic load-balancing.
Active/Passive (standby
failover)
I/O uses only one path. If the active path fails, DM-Multipath switches I/
O to a standby path. This is the default configuration.
Note
DM-Multipath can provide failover in the case of path failure, such as in a SAN
fabric. Disk media failure must be handled by using either a software or hardware
RAID solution.
17.7.1 Configuring Multipathing
The procedure in this section demonstrates how to set up a simple multipath configuration.
To configure multipathing on a server with access to SAN-attached storage:
1. Install the device-mapper-multipath package:
# yum install device-mapper-multipath
2. You can now choose one of two configuration paths:
178
Configuring Multipathing
• To set up a basic standby failover configuration without editing the /etc/multipath.conf
configuration file, enter the following command:
# mpathconf --enable --with_multipathd y --with_chkconfig y
This command also starts the multipathd service and configures the service to start after system
reboots.
Skip the remaining steps of this procedure.
• To edit /etc/multipath.conf and set up a more complex configuration such as active/active,
follow the remaining steps in this procedure.
3. Initialize the /etc/multipath.conf file:
# mpathconf --enable
4. Edit /etc/multipath.conf and define defaults, blacklist, blacklist_exceptions,
multipaths, and devices sections as required, for example:
defaults {
udev_dir
polling_interval
path_selector
path_grouping_policy
getuid_callout
prio
path_checker
rr_min_io
max_fds
rr_weight
failback
no_path_retry
user_friendly_names
}
/dev
10
"round-robin 0"
multibus
"/lib/udev/scsi_id --whitelisted --device=/dev/%n"
alua
readsector0
100
8192
priorities
immediate
fail
yes
blacklist {
# Blacklist by WWID
wwid "*"
# Blacklist by device name
devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"
# Blacklist by device type
device {
vendor
"COMPAQ "
product
"HSV110 (C)COMPAQ"
}
}
blacklist_exceptions {
wwid "3600508b4000156d700012000000b0000"
wwid "360000970000292602744533032443941"
}
multipaths {
multipath {
wwid
alias
path_grouping_policy
path_checker
path_selector
failback
rr_weight
3600508b4000156d700012000000b0000
blue
multibus
readsector0
"round-robin 0"
manual
priorities
179
Configuring Multipathing
no_path_retry
}
multipath {
wwid
alias
}
5
360000970000292602744533032443941
green
}
devices {
device {
vendor
product
path_grouping_policy
getuid_callout
path_selector
features
hardware_handler
path_checker
prio
rr_weight
rr_min_io
}
}
"SUN"
"(StorEdge 3510|T4"
multibus
"/sbin/scsi_id --whitelisted --device=/dev/%n"
"round-robin 0"
"0"
"0"
directio
const
uniform
1000
The sections have the following purposes:
defaults
Defines default multipath settings, which can be overridden by settings in
the devices section, and which in turn can be overridden by settings in
the multipaths section.
blacklist
Defines devices that are excluded from multipath topology discovery.
Blacklisted devices cannot subsumed by a multipath device.
The example shows the three ways that you can use to exclude devices:
by WWID (wwid), by device name (devnode), and by device type
(device).
blacklist_exceptions
Defines devices that are included in multipath topology discovery, even if
the devices are implicitly or explicitly listed in the blacklist section.
multipaths
Defines settings for a multipath device that is identified by its WWID.
The alias attribute specifies the name of the multipath device as it will
appear in /dev/mapper instead of a name based on either the WWID or
the multipath group number.
To obtain the WWID of a SCSI device, use the scsi_id command:
# scsi_id --whitelisted --replace-whitespace --device=device_name
devices
Defines settings for individual types of storage controller. Each controller
type is identified by the vendor, product, and optional revision
settings, which must match the information in sysfs for the device.
You can find details of the storage arrays that DM-Multipath supports
and their default configuration values in /usr/share/doc/devicemapper-multipath-version/multipath.conf.defaults, which
you can use as the basis for entries in /etc/multipath.conf.
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Configuring Multipathing
To add a storage device that DM-Multipath does not list as being
supported, obtain the vendor, product, and revision information from the
vendor, model, and rev files under /sys/block/device_name/
device.
The following entries in /etc/multipath.conf would be appropriate for setting up active/passive
multipathing to an iSCSI LUN with the specified WWID.
defaults {
user_friendly_names
getuid_callout
}
yes
"/bin/scsi_id --whitelisted --replace-whitespace --device=/dev/%n”
multipaths {
multipath {
wwid 360000970000292602744533030303730
}
}
In this standby failover configuration, I/O continues through a remaining active network interface if a
network interfaces fails on the iSCSI initiator.
For more information about configuring entries in /etc/multipath.conf, refer to the
multipath.conf(5) manual page.
5. Start the multipathd service and configure the service to start after system reboots:
# service multipathd start
# chkconfig multipathd on
Multipath devices are identified in /dev/mapper by their World Wide Identifier (WWID), which is globally
unique. Alternatively, if you set the value of user_friendly_names to yes in the defaults section of
/etc/multipath.conf or by specifying the --user_friendly_names n option to mpathconf, the
device is named mpathN where N is the multipath group number. An alias attribute in the multipaths
section of /etc/multipath.conf specifies the name of the multipath device instead of a name based
on either the WWID or the multipath group number.
You can use the multipath device in /dev/mapper to reference the storage in the same way as you would
any other physical storage device. For example, you can configure it as an LVM physical volume, file
system, swap partition, Automatic Storage Management (ASM) disk, or raw device.
To display the status of DM-Multipath, use the mpathconf command, for example:
# mpathconf
multipath is enabled
find_multipaths is enabled
user_friendly_names is enabled
dm_multipath modules is loaded
multipathd is chkconfiged on
To display the current multipath configuration, specify the -ll option to the multipath command, for
example:
# multipath -ll
mpath1(360000970000292602744533030303730) dm-0 SUN,(StorEdge 3510|T4
size=20G features=‘0’ hwhandler=‘0’ wp=rw
|-+- policy=‘round-robin 0’ prio=1 status=active
| ‘- 5:0:0:2 sdb 8:16
active ready running
‘-+- policy=‘round-robin 0’ prio=1 status=active
‘- 5:0:0:3 sdc 8:32
active ready running
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Configuring Multipathing
In this example, /dev/mapper/mpath1 subsumes two paths (/dev/sdb and /dev/sdc) to 20 GB of
storage in an active/active configuration using round-robin I/O path selection. The WWID that identifies the
storage is 360000970000292602744533030303730 and the name of the multipath device under sysfs
is dm-0.
If you edit /etc/multipath.conf, restart the multipathd service to make it re-read the file:
# service multipathd restart
For more information, see the mpathconf(8), multipath(8), multipathd(8),
multipath.conf(5), and scsi_id(8) manual pages.
182
Chapter 18 File System Administration
Table of Contents
18.1 Making File Systems ...............................................................................................................
18.2 Mounting File Systems ............................................................................................................
18.2.1 About Mount Options ....................................................................................................
18.3 About the File System Mount Table .........................................................................................
18.4 Configuring the Automounter ...................................................................................................
18.5 Mounting a File Containing a File System Image ......................................................................
18.6 Creating a File System on a File .............................................................................................
18.7 Checking and Repairing a File System ....................................................................................
18.7.1 Changing the Frequency of File System Checking .........................................................
18.8 About Access Control Lists ......................................................................................................
18.8.1 Configuring ACL Support ..............................................................................................
18.8.2 Setting and Displaying ACLs .........................................................................................
18.9 About Disk Quotas ..................................................................................................................
18.9.1 Enabling Disk Quotas on File Systems ..........................................................................
18.9.2 Assigning Disk Quotas to Users and Groups .................................................................
18.9.3 Setting the Grace Period ..............................................................................................
18.9.4 Displaying Disk Quotas .................................................................................................
18.9.5 Enabling and Disabling Disk Quotas .............................................................................
18.9.6 Reporting on Disk Quota Usage ...................................................................................
18.9.7 Maintaining the Accuracy of Disk Quota Reporting .........................................................
183
184
185
186
187
188
188
189
190
190
191
191
192
193
193
194
194
194
194
195
This chapter describes how to create, mount, check, and repair file systems, how to configure Access
Control Lists, how to configure and manage disk quotas.
18.1 Making File Systems
The mkfs command build a file system on a block device:
# mkfs [options] device
mkfs is a front end for builder utilities in /sbin such as mkfs.ext4. You can use either the mkfs
command with the -t fstype option or the builder utility to specify the type of file system to build. For
example, the following commands are equivalent ways of creating an ext4 file system with the label
Projects on the device /dev/sdb1:
# mkfs -t ext4 -L Projects /dev/sdb1
# mkfs.ext4 -L Projects /dev/sdb1
If you do not specify the file system type to makefs , it creates an ext2 file system.
To display the type of a file system, use the blkid command:
# blkid /dev/sdb1
/dev/sdb1: UUID="ad8113d7-b279-4da8-b6e4-cfba045f66ff" TYPE="ext4" LABEL="Projects"
The blkid command also display information about the device such as its UUID and label.
Each file system type supports a number of features that you can enable or disable by specifying additional
options to mkfs or the build utility. For example, you can use the -J option to specify the size and location
of the journal used by the ext3 and ext4 file system types.
For more information, see the blkid(8), mkfs(8), and mkfs.fstype(8) manual pages.
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Mounting File Systems
18.2 Mounting File Systems
To access a file system's contents, you must attach its block device to a mount point in the directory
hierarchy. You can use the mkdir command to create a directory for use as a mount point, for example:
# mkdir /var/projects
You can use an existing directory as a mount point, but its contents are hidden until you unmount the
overlying file system.
The mount command attaches the device containing the file system to the mount point:
# mount [options] device mount_point
You can specify the device by its name, UUID, or label. For example, the following commands are
equivalent ways of mounting the file system on the block device /dev/sdb1:
# mount /dev/sdb1 /var/projects
# mount UUID="ad8113d7-b279-4da8-b6e4-cfba045f66ff" /var/projects
# mount LABEL="Projects" /var/projects
If you do not specify any arguments, mount displays all file systems that the system currently has
mounted, for example:
# mount
/dev/mapper/vg_host01-lv_root on / type ext4 (rw)
...
In this example, the LVM logical volume /dev/mapper/vg_host01-lv_root is mounted on /. The file
system type is ext4 and is mounted for both reading and writing. (You can also use the command cat /
proc/mounts to display information about mounted file systems.)
The df command displays information about home much space remains on mounted file systems, for
example:
# df -h
Filesystem
/dev/mapper/vg_host01-lv_root
...
Size
36G
Used Avail Use% Mounted on
12G
22G 36% /
You can use the -B (bind) option to the mount command to attach a block device at multiple mount points.
You can also remount part of a directory hierarchy, which need not be a complete file system, somewhere
else. For example, the following command mounts /var/projects/project1 on /mnt:
# mount -B /var/projects/project1 /mnt
Each directory hierarchy acts as a mirror of the other. The same files are accessible in either location,
although any submounts are not replicated. These mirrors do not provide data redundancy.
You can also mount a file over another file, for example:
# touch /mnt/foo
# mount -B /etc/hosts /mnt/foo
In this example, /etc/hosts and /mnt/foo represent the same file. The existing file that acts as a
mount point is not accessible until you unmount the overlying file.
The -B option does not recursively attach any submounts below a directory hierarchy. To include
submounts in the mirror, use the -R (recursive bind) option instead.
When you use -B or -R, the file system mount options remain the same as those for the original mount
point. To modify, the mount options, use a separate remount command, for example:
184
About Mount Options
# mount -o remount,ro /mnt/foo
You can mark the submounts below a mount point as being shared, private, or slave:
mount --make-shared
mount_point
Any mounts or unmounts below the specified mount point propagate to
any mirrors that you create, and this mount hierarchy reflects mounts or
unmount changes that you make to other mirrors.
mount --make-private
mount_point
Any mounts or unmounts below the specified mount point do not
propagate to other mirrors, nor does this mount hierarchy reflect mounts
or unmount changes that you make to other mirrors.
mount --make-slave
mount_point
Any mounts or unmounts below the specified mount point do not
propagate to other mirrors, but this mount hierarchy does reflect mounts
or unmount changes that you make to other mirrors.
To prevent a mount from being mirrored by using the -B or -R options, mark its mount point as being
unbindable:
# mount --make-unbindable mount_point
To move a mounted file system, directory hierarchy, or file between mount points, use the -M option, for
example:
# touch /mnt/foo
# mount -M /mnt/foo /mnt/bar
To unmount a file system, use the umount command, for example:
# umount /var/projects
Alternatively, you can specify the block device provided that it is mounted on only one mount point.
For more information, see the mount(8) and umount(8) manual pages.
18.2.1 About Mount Options
To modify the behavior of mount, use the –o flag followed by a comma-separated list of options or specify
the options in the /etc/fstab file. The following are some of the options that are available:
auto
Allows the file system to be mounted automatically by using the mount –a command.
exec
Allows the execution of any binary files located in the file system.
loop
Uses a loop device (/dev/loop*) to mount a file that contains a file system image. See
Section 18.5, “Mounting a File Containing a File System Image”, Section 18.6, “Creating a File
System on a File”, and the losetup(8) manual page.
Note
The default number of available loop devices is 8. You can use the
kernel boot parameter max_loop=N to configure up to 255 devices.
Alternatively, add the following entry to /etc/modprobe.conf:
options loop max_loop=N
where N is the number of loop devices that you require (from 0 to 255),
and reboot the system.
185
About the File System Mount Table
noauto
Disallows the file system from being mounted automatically by using mount –a.
noexec
Disallows the execution of any binary files located in the file system.
nouser
Disallows any user other than root from mounting or unmounting the file system.
remount
Remounts the file system if it is already mounted. You would usually combine this option with
another option such as ro or rw to change the behavior of a mounted file system.
ro
Mounts a file system as read-only.
rw
Mounts a file system for reading and writing.
user
Allows any user to mount or unmount the file system.
For example, mount /dev/sdd1 as /test with read-only access and only root permitted to mount or
unmount the file system:
# mount –o nouser,ro /dev/sdd1 /test
Mount an ISO image file on /mount/cdrom with read-only access by using the loop device:
# mount -o ro,loop ./OracleLinux-R6-U1-Server-x86_64-dvd.iso /media/cdrom
Remount the /test file system with both read and write access, but do not permit the execution of any
binary files that are located in the file system:
# mount -o remount,rw,noexec /test
18.3 About the File System Mount Table
The /etc/fstab file contains the file system mount table, and provides all the information that the mount
command needs to mount block devices or to implement binding of mounts. If you add a file system, create
the appropriate entry in /etc/fstab to ensure that the file system is mounted at boot time. The following
are sample entries from /etc/fstab:
/dev/sda1
/dev/sda2
/dev/sda3
/boot
/
swap
ext4
ext4
swap
defaults
defaults
defaults
1 2
1 1
0 0
The first field is the device to mount specified by the device name, UUID, or device label, or the
specification of a remote file system. A UUID or device label is preferable to a device name if the device
name could change, for example:
LABEL=Projects
/var/projects
ext4
defaults
1 2
The second field is either the mount point for a file system or swap to indicate a swap partition.
The third field is the file system type, for example ext4 or swap.
The fourth field specifies any mount options.
The fifth column is used by the dump command. A value of 1 means dump the file system; 0 means the file
system does not need to be dumped.
The sixth column is used by the file system checker, fsck, to determine in which order to perform file
system checks at boot time. The value should be 1 for the root file system, 2 for other file systems. A
value of 0 skips checking, as is appropriate for swap, file systems that are not mounted at boot time, or for
binding of existing mounts.
186
Configuring the Automounter
For bind mounts, only the first four fields are specified, for example:
path
mount_point
none
bind
The first field specifies the path of the file system, directory hierarchy, or file that is to be mounted on
the mount point specified by the second field. The mount point must be a file if the path specifies a file;
otherwise, it must be a directory. The third and fourth fields are specified as none and bind.
For more information, see the fstab(5) manual page.
18.4 Configuring the Automounter
The automounter mounts file systems when they are accessed, rather than maintaining connections for
those mounts at all times. When a file system becomes inactive for more than a certain period of time,
the automounter unmounts it. Using automounting frees up system resources and improves system
performance.
The automounter consists of two components: the autofs kernel module and the automount user-space
daemon.
To configure a system to use automounting:
1. Install the autofs package and any other packages that are required to support remote file systems:
# yum install autofs
2. Edit the /etc/auto.master configuration file to define map entries. Each map entry specifies a
mount point and a map file that contains definitions of the remote file systems that can be mounted, for
example:
//misc
/net
/etc/auto.direct
/etc/auto.misc
-hosts
Here, the /-, /misc, and /net entries are examples of a direct map, an indirect map, and a host map
respectively. Direct map entries always specify /- as the mount point. Host maps always specify the
keyword -hosts instead of a map file.
A direct map contains definitions of directories that are automounted at the specified absolute path. In
the example, the auto.direct map file might contain an entry such as:
/usr/man
-fstype=nfs,ro,soft
host01:/usr/man
This entry mounts the file system /usr/man exported by host01 using the options ro and soft, and
creates the /usr/man mount point if it does not already exist. If the mount point already exists , the
mounted file system hides any existing files that it contains.
As the default file system type is NFS, the previous example can be shortened to read:
/usr/man
-ro,soft
host01:/usr/man
An indirect map contains definitions of directories (keys) that are automounted relative to the mount
point (/misc) specified in /etc/auto.master. In the example, the /etc/auto.misc map file might
contain entries such as the following:
xyz
cd
abc
fenetres
-ro,soft
host01:/xyz
-fstype=iso9600,ro,nosuid,nodev
:/dev/cdrom
-fstype=ext3
:/dev/hda1
-fstype=cifs,credentials=credfile
://fenetres/c
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Mounting a File Containing a File System Image
The /misc directory must already exist, but the automounter creates a mount point for the keys xyz,
cd , and so on if they does not already exist, and removes them when it unmounts the file system. For
example, entering a command such as ls /misc/xyz causes the automounter to the mount the /
xyz directory exported by host01 as /misc/xyz.
The cd and abc entries mount local file systems: an ISO image from the CD-ROM drive on /misc/cd
and an ext3 file system from /dev/hda1 on /misc/abc. The fenetres entry mounts a Samba share
as /misc/fenetres.
If a host map entry exists and a command references an NFS server by name relative to the mount
point (/net), the automounter mounts all directories that the server exports below a subdirectory of
the mount point named for the server. For example, the command cd /net/host03 causes the
automounter to mount all exports from host03 below the /net/host03 directory. By default, the
automounter uses the mount options nosuid,nodev,intr options unless you override the options in
the host map entry, for example:
/net
-hosts
-suid,dev,nointr
Note
The name of the NFS server must be resolvable to an IP address in DNS or in
the /etc/hosts file.
For more information, including details of using maps with NIS, NIS+, and LDAP, see the
hosts.master(5) manual page.
3. Start the autofs service, and configure the service to start following a system reboot:
# service autofs start
# chkconfig autofs on
You can configure various settings for autofs in /etc/sysconfig/autofs, such as the idle timeout
value after which a file system is automatically unmounted.
If you modify /etc/auto.master or /etc/sysconfig/autofs, restart the autofs service to make it
re-read these files:
# service autofs restart
For more information, see the automount(8), autofs(5), and auto.master(5) manual pages.
18.5 Mounting a File Containing a File System Image
A loop device allows you to access a file as a block device. For example, to mount a file that contains a
DVD ISO image on the directory mount point /ISO:
# mount -t iso9660 -o ro,loop /var/ISO_files/V33411-01.iso /ISO
If required, create a permanent entry for the file system in /etc/fstab:
/var/ISO_files/V33411-01.iso
/ISO
iso9660
18.6 Creating a File System on a File
To create a file system on a file within another file system:
1. Create an empty file of the required size, for example:
188
ro,loop
0 0
Checking and Repairing a File System
# dd if=/dev/zero of=/fsfile bs=1024 count=1000000
1000000+0 records in
1000000+0 records out
1024000000 bytes (1.0 GB) copied, 8.44173 s, 121 MB/s
2. Create a file system on the file:
# mkfs.ext4 -F /fsfile
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
62592 inodes, 250000 blocks
12500 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=260046848
8 block groups
32768 blocks per group, 32768 fragments per group
7824 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 33 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
3. Mount the file as a file system by using a loop device:
# mount -o loop /fsfile /mnt
The file appears as a normal file system:
# mount
...
/fsfile on /mnt type ext4 (rw,loop=/dev/loop0)
# df -h
Filesystem
Size Used Avail Use% Mounted on
...
/fsfile
962M
18M 896M
2% /mnt
If required, create a permanent entry for the file system in /etc/fstab:
/fsfile
/mnt
ext4
rw,loop
0 0
18.7 Checking and Repairing a File System
The fsck utility checks and repairs file systems. For file systems other than / (root) and /boot, mount
invokes file system checking if more than a certain number of mounts have occurred or more than 180
days have elapsed without checking having being performed. You might want to run fsck manually if a file
system has not been checked for several months.
Warning
Running fsck on a mounted file system can corrupt the file system and cause data
loss.
To check and repair a file system:
189
Changing the Frequency of File System Checking
1. Unmount the file system:
# umount filesystem
2. Use the fsck command to check the file system:
# fsck [-y] filesystem
filesystem be a device name, a mount point, or a label or UUID specifier, for example:
# fsck UUID=ad8113d7-b279-4da8-b6e4-cfba045f66ff
By default, fsck prompts you to choose whether it should apply a suggested repair to the file system. If
you specify the -y option, fsck assumes a yes response to all such questions.
For the ext2, ext3, and ext4 file system types, other commands that are used to perform file system
maintenance include dumpe2fs and debugfs. dumpe2fs prints super block and block group information
for the file system on a specified device. debugfs is an interactive file system debugger that requires
expert knowledge of the file system architecture. Similar commands exist for most file system types and
also require expert knowledge.
For more information, see the fsck(8) manual page.
18.7.1 Changing the Frequency of File System Checking
To change the number of mounts before the system automatically checks the file system for consistency:
# tune2fs -c mount_count device
where device specifies the block device corresponding to the file system.
A mount_count of 0 or -1 disables automatic checking based on the number of mounts.
Tip
Specifying a different value of mount_count for each file system reduces the
probability that the system checks all the file systems at the same time.
To specify the maximum interval between file system checks:
# tune2fs -i interval[unit] device
The unit can be d, w, or m for days, weeks, or months. The default unit is d for days. An interval of 0
disables checking that is based on the time that has elapsed since the last check. Even if the interval is
exceeded, the file system is not checked until it is next mounted.
For more information, see the tune2fs(8) manual page.
18.8 About Access Control Lists
POSIX Access Control Lists (ACLs) provide a richer access control model than traditional UNIX
Discretionary Access Control (DAC) that sets read, write, and execute permissions for the owner, group,
and all other system users. You can configure ACLs that define access rights for more than just a single
user or group, and specify rights for programs, processes, files, and directories. If you set a default ACL on
a directory, its descendents inherit the same rights automatically. You can use ACLs with btrfs, ext3, ext4,
OCFS2, and XFS file systems and with mounted NFS file systems.
An ACL consists of a set of rules that specify how a specific user or group can access the file or directory
with which the ACL is associated. A regular ACL entry specifies access information for a single file or
190
Configuring ACL Support
directory. A default ACL entry is set on directories only, and specifies default access information for any file
within the directory that does not have an access ACL.
18.8.1 Configuring ACL Support
To enable ACL support:
1. Install the acl package:
# yum install acl
2. Edit /etc/fstab and change the entries for the file systems with which you want to use ACLs so that
they include the appropriate option that supports ACLs, for example:
LABEL=/work
/work
ext4
acl
0 0
For mounted Samba shares, use the cifsacl option instead of acl.
3. Remount the file systems, for example:
# mount -o remount /work
18.8.2 Setting and Displaying ACLs
To add or modify the ACL rules for file, use the setfacl command:
# setfacl -m rules file ...
The rules take the following forms:
[d:]u:user[:permissions]
Sets the access ACL for the user specified by name or user ID. The
permissions apply to the owner if a user is not specified.
[d:]g:group[:permissions]
Sets the access ACL for a group specified by name or group ID. The
permissions apply to the owning group if a group is not specified.
[d:]m[:][:permissions]
Sets the effective rights mask, which is the union of all permissions of
the owning group and all of the user and group entries.
[d:]o[:][:permissions]
Sets the access ACL for other (everyone else to whom no other rule
applies).
The permissions are r, w, and x for read, write, and execute as used with chmod.
The d: prefix is used to apply the rule to the default ACL for a directory.
To display a file's ACL, use the getfacl command, for example:
# getfacl foofile
# file: foofile
# owner: bob
# group: bob
user::rwuser::fiona:r-user::jack:rwuser::jill:rwgroup::r-mask::r-other::r--
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About Disk Quotas
If extended ACLs are active on a file, the -l option to ls displays a plus sign (+) after the permissions, for
example:
# ls -l foofile
-rw-r--r--+ 1 bob bob
105322 Apr 11 11:02 foofile
The following are examples of how to set and display ACLs for directories and files.
Grant read access to a file or directory by a user.
# setfacl -m u:user:r file
Display the name, owner, group, and ACL for a file or directory.
# getfacl file
Remove write access to a file for all groups and users by modifying the effective rights mask rather than
the ACL.
# setfacl -m m::rx file
The -x option removes rules for a user or group.
Remove the rules for a user from the ACL of a file.
# setfacl -x u:user file
Remove the rules for a group from the ACL of a file.
# setfacl -x g:group file
The -b option removes all extended ACL entries from a file or directory.
# setfacl –b file
Copy the ACL of file f1 to file f2.
# getfacl f1 | setfacl --set-file=- f2
Set a default ACL of read and execute access for other on a directory:
# setfacl -m d:o:rx directory
Promote the ACL settings of a directory to default ACL settings that can be inherited.
# getfacl --access directory | setfacl -d -M- directory
The -k option removes the default ACL from a directory.
# setfacl –k directory
For more information, see the acl(5), setfacl(1), and getfacl(1) manual pages.
18.9 About Disk Quotas
Note
For information about how to configure quotas for the XFS file system, see
Section 19.23, “Setting Quotas on an XFS File System”.
You can set disk quotas to restrict the amount of disk space (blocks) that users or groups can use, to limit
the number of files (inodes) that users or groups can create, and to notify you when usage is reaching a
192
Enabling Disk Quotas on File Systems
specified limit. A hard limit specifies the maximum number of blocks or inodes available to a user or group
on the file system. Users or groups can exceed a soft limit for a period of time known as a grace period.
18.9.1 Enabling Disk Quotas on File Systems
To enable user or group disk quotas on a file system:
1. Install or update the quota package:
# yum install quota
2. Include the usrquota or grpquota options in the file system's /etc/fstab entry, for example:
/dev/sdb1
/home
ext4
usrquota,grpquota
0 0
3. Remount the file system:
# mount –o remount /home
4. Create the quota database files:
# quotacheck –cug /home
This command creates the files aquota.user and aquota.group in the root of the file system (/
home in this example).
For more information, see the quotacheck(8) manual page.
18.9.2 Assigning Disk Quotas to Users and Groups
To configure the disk quota for a user:
1. Enter the following command for a user:
# edquota username
or for a group:
# edquota –g group
The command opens a text file opens in the default editor defined by the EDITOR environment variable,
allowing you to specify the limits for the user or group, for example:
Disk quotas for user guest (uid 501)
Filesystem blocks soft hard inodes
/dev/sdb1
10325
0
0
1054
soft
0
hard
0
The blocks and inodes entries show the user's currently usage on a file system.
Tip
Setting a limit to 0 disables quota checking and enforcement for the
corresponding blocks or inodes category.
2. Edit the soft and hard block limits for number of blocks and inodes, and save and close the file.
Alternatively, you can use the setquota command to configure quota limits from the command-line. The –
p option allows you to apply quota settings from one user or group to another user or group.
For more information, see the edquota(8) and setquota(8) manual pages.
193
Setting the Grace Period
18.9.3 Setting the Grace Period
To configure the grace period for soft limits:
1. Enter the following command:
# edquota -t
The command opens a text file opens in the default editor defined by the EDITOR environment variable,
allowing you to specify the grace period, for example:
Grace period before enforcing soft limits for users:
Time units may be: days, hours, minutes, or seconds
Filesystem
Block grace period
Inode grace period
/dev/sdb1
7days
7days
2. Edit the grace periods for the soft limits on the number of blocks and inodes, and save and close the
file.
For more information, see the edquota(8) manual page.
18.9.4 Displaying Disk Quotas
To display a user's disk usage:
# quota username
To display a group's disk usage:
# quota -g group
To display information about file systems where usage is over the quota limits:
# quota -q
Users can also use the quota command to display their own and their group's usage.
For more information, see the quota(1) manual page.
18.9.5 Enabling and Disabling Disk Quotas
To disable disk quotas for all users, groups on a specific file system:
# quotaoff -guv filesystem
To disable disk quotas for all users, groups, and file systems:
# quotaoff -aguv
To re-enable disk quotas for all users, groups, and file systems:
# quotaon -aguv
For more information, see the quotaon(1) manual page.
18.9.6 Reporting on Disk Quota Usage
To display the disk quota usage for a file system:
# repquota filesystem
194
Maintaining the Accuracy of Disk Quota Reporting
To display the disk quota usage for all file systems:
# repquota -a
For more information, see the repquota(8) manual page.
18.9.7 Maintaining the Accuracy of Disk Quota Reporting
Uncontrolled system shutdowns can lead to inaccuracies in disk quota reports.
To rebuild the quota database for a file system:
1. Disable disk quotas for the file system:
# quotaoff -guv filesystem
2. Unmount the file system:
# umount filesystem
3. Enter the following command to rebuild the quota databases:
# quotacheck -guv filesystem
4. Mount the file system:
# mount filesystem
5. Enable disk quotas for the file system:
# quotaoff -guv filesystem
For more information, see the quotacheck(8) manual page.
195
196
Chapter 19 Local File System Administration
Table of Contents
19.1
19.2
19.3
19.4
19.5
19.6
19.7
About Local File Systems ........................................................................................................ 198
About the Btrfs File System ..................................................................................................... 199
Creating a Btrfs File System .................................................................................................... 199
Modifying a Btrfs File System .................................................................................................. 201
Compressing and Defragmenting a Btrfs File System ................................................................ 201
Resizing a Btrfs File System ................................................................................................... 202
Creating Subvolumes and Snapshots ....................................................................................... 202
19.7.1 Cloning Virtual Machine Images and Linux Containers ................................................... 204
19.8 Using the Send/Receive Feature ............................................................................................. 204
19.8.1 Using Send/Receive to Implement Incremental Backups ................................................. 205
19.9 Using Quota Groups ............................................................................................................... 205
19.10 Replacing Devices on a Live File System ............................................................................... 206
19.11 Creating Snapshots of Files ................................................................................................... 206
19.12 Converting an Ext2, Ext3, or Ext4 File System to a Btrfs File System ....................................... 206
19.12.1 Converting a Non-root File System .............................................................................. 207
19.12.2 Converting the root File System .................................................................................. 207
19.12.3 Mounting the Image of the Original File System ........................................................... 209
19.12.4 Deleting the Snapshot of the Original File System ........................................................ 209
19.12.5 Recovering an Original Non-root File System ............................................................... 209
19.13 Installing a Btrfs root File System .......................................................................................... 210
19.13.1 Setting up a New NFS Server ..................................................................................... 210
19.13.2 Configuring an Existing NFS Server ............................................................................ 211
19.13.3 Setting up a New HTTP Server ................................................................................... 211
19.13.4 Configuring an Existing HTTP Server .......................................................................... 212
19.13.5 Setting up a Network Installation Server ...................................................................... 213
19.13.6 Installing from a Network Installation Server ................................................................. 214
19.13.7 About the Installation root File System ......................................................................... 215
19.13.8 Creating Snapshots of the root File System ................................................................. 216
19.13.9 Mounting Alternate Snapshots as the root File System ................................................. 216
19.13.10 Deleting Snapshots of the root File System ................................................................ 216
19.14 Converting a Non-root Ext2 File System to Ext3 ..................................................................... 217
19.15 Converting a root Ext2 File System to Ext3 ............................................................................ 217
19.16 Creating a Local OCFS2 File System ..................................................................................... 219
19.17 About the XFS File System ................................................................................................... 219
19.17.1 About External XFS Journals ...................................................................................... 220
19.17.2 About XFS Write Barriers ........................................................................................... 221
19.17.3 About Lazy Counters .................................................................................................. 221
19.18 Installing the XFS Packages .................................................................................................. 221
19.19 Creating an XFS File System ................................................................................................ 221
19.20 Modifying an XFS File System ............................................................................................... 222
19.21 Growing an XFS File System ................................................................................................. 223
19.22 Freezing and Unfreezing an XFS File System ........................................................................ 223
19.23 Setting Quotas on an XFS File System .................................................................................. 223
19.23.1 Setting Project Quotas ................................................................................................ 224
19.24 Backing up and Restoring XFS File Systems .......................................................................... 225
19.25 Defragmenting an XFS File System ....................................................................................... 227
19.26 Checking and Repairing an XFS File System ......................................................................... 227
197
About Local File Systems
This chapter describes administration tasks for the btrfs, ext3, ext4, OCFS2, and XFS local file systems.
19.1 About Local File Systems
Oracle Linux supports a large number of local file system types that you can configure on block devices,
including:
btrfs
Btrfs is a copy-on-write file system that is designed to address the expanding scalability
requirements of large storage subsystems. It supports snapshots, a roll-back capability,
checksum functionality for data integrity, transparent compression, and integrated logical volume
management.
The maximum supported file or file system size is 16 EB, although these limits are untested. Btrfs
requires the Unbreakable Enterprise Kernel Release 2 (2.6.39) or the Unbreakable Enterprise
Kernel Release 3 (3.8.13).
For more information, see Section 19.2, “About the Btrfs File System”.
ext3
The ext3 file system includes journaling capabilities to improve reliability and availability.
Consistency checks after a power failure or an uncontrolled system shutdown are unnecessary.
ext2 file systems are upgradeable to ext3 without reformatting.
See Section 19.14, “Converting a Non-root Ext2 File System to Ext3” and Section 19.15,
“Converting a root Ext2 File System to Ext3”.
The maximum supported file and file system sizes are 2 TB and 16 TB.
ext4
In addition to the features of ext3, the ext4 file system supports extents (contiguous physical
blocks), pre-allocation, delayed allocation, faster file system checking, more robust journaling, and
other enhancements.
The maximum supported file or file system size is 16 TB.
ocfs2
Although intended as a general-purpose, high-performance, high-availability, shared-disk file
system intended for use in clusters, it is possible to use Oracle Cluster File System version 2
(OCFS2) as a standalone, non-clustered file system.
Although it might seem that there is no benefit in mounting OCFS2 locally as compared to
alternative file systems such as ext4 or btrfs, you can use the reflink command with OCFS2
to create copy-on-write clones of individual files in a similar way to using the cp --reflink
command with the btrfs file system. Typically, such clones allow you to save disk space when
storing multiple copies of very similar files, such as VM images or Linux Containers. In addition,
mounting a local OCFS2 file system allows you to subsequently migrate it to a cluster file system
without requiring any conversion.
See Section 19.16, “Creating a Local OCFS2 File System”.
The maximum supported file or file system size is 16 TB.
vfat
The vfat file system (also known as FAT32) was originally developed for MS-DOS. It does not
support journaling and lacks many of the features that are available with other file system types. It
is mainly used to exchange data between Microsoft Windows and Oracle Linux systems.
The maximum supported file size or file system size is 2 GB.
198
About the Btrfs File System
xfs
XFS is a high-performance journaling file system, which provides high scalability for I/O threads,
file system bandwidth, file and file system size, even when the file system spans many storage
devices.
The maximum supported file or file system size is 100 TB. XFS is supported only on the
x86_64 architecture and requires the Unbreakable Enterprise Kernel Release 2 (2.6.39) or the
Unbreakable Enterprise Kernel Release 3 (3.8.13).
For more information, see Section 19.17, “About the XFS File System”.
To see what file system types your system supports, use the following command:
# ls /sbin/mkfs.*
/sbin/mkfs.btrfs
/sbin/mkfs.cramfs
/sbin/mkfs.ext2
/sbin/mkfs.ext3
/sbin/mkfs.ext4
/sbin/mkfs.ext4dev
/sbin/mkfs.msdos
/sbin/mkfs.vfat
/sbin/mkfs.xfs
These executables are used to make the file system type specified by their extension. mkfs.msdos and
mkfs.vfat are alternate names for mkdosfs. mkfs.cramfs creates a compressed ROM, read-only
cramfs file system for use by embedded or small-footprint systems.
19.2 About the Btrfs File System
The btrfs file system is designed to meet the expanding scalability requirements of large storage
subsystems. As the btrfs file system uses B-trees in its implementation, its name derives from the name of
those data structures, although it is not a true acronym. A B-tree is a tree-like data structure that enables
file systems and databases to efficiently access and update large blocks of data no matter how large the
tree grows.
The btrfs file system provides the following important features:
• Copy-on-write functionality allows you to create both readable and writable snapshots, and to roll back a
file system to a previous state, even after you have converted it from an ext3 or ext4 file system.
• Checksum functionality ensures data integrity.
• Transparent compression saves disk space.
• Transparent defragmentation improves performance.
• Integrated logical volume management allows you to implement RAID 0, RAID 1, or RAID 10
configurations, and to dynamically add and remove storage capacity.
Starting with Oracle Linux 6 Update 3, the UEK Boot ISO (which boots the Unbreakable Enterprise Kernel
as the installation kernel) allows you to configure a btrfs root file system. Prior to Oracle Linux 6 Update 3,
you could not create a btrfs root file system during installation. For more information, see Section 19.13,
“Installing a Btrfs root File System”.
You can find more information about the btrfs file system at https://btrfs.wiki.kernel.org/index.php/
Main_Page.
19.3 Creating a Btrfs File System
Note
If the btrfs-progs package is not already installed on your system, use yum to
install it.
199
Creating a Btrfs File System
You can use the mkfs.btrfs command to create a btrfs file system that is laid out across one or more
block devices. The default configuration is to stripe the file system data and to mirror the file system
metadata across the devices. If you specify a single device, the metadata is duplicated on that device
unless you specify that only one copy of the metadata is to be used. The devices can be simple disk
partitions, loopback devices (that is, disk images in memory), multipath devices, or LUNs that implement
RAID in hardware.
The following table illustrates how to use the mkfs.btrfs command to create various btrfs configurations.
Command
Description
mkfs.btrfs block_device
Create a btrfs file system on a single device. For example:
mkfs.btrfs /dev/sdb1
mkfs.btrfs -L label block_device
Create a btrfs file system with a label that you can use
when mounting the file system. For example:
mkfs.btrfs -L myvolume /dev/sdb2
Note
The device must correspond to a
partition if you intend to mount it by
specifying the name of its label.
mkfs.btrfs -m single block_device
Create a btrfs file system on a single device, but do not
duplicate the metadata on that device. For example:
mkfs.btrfs -m single /dev/sdc
mkfs.btrfs block_device1
block_device2 ...
Stripe the file system data and mirror the file system
metadata across several devices. For example:
mkfs.btrfs /dev/sdd /dev/sde
mkfs.btrfs -m raid0 block_device1
block_device2 ...
Stripe both the file system data and metadata across
several devices. For example:
mkfs.btrfs -m raid0 /dev/sdd /dev/sde
mkfs.btrfs -d raid1 block_device1
block_device2 ...
Mirror both the file system data and metadata across
several devices. For example:
mkfs.btrfs -d raid1 /dev/sdd /dev/sde
mkfs.btrfs -d raid10 -m raid10
block_device1 block_device2
block_device3 block_device4
Stripe the file system data and metadata across several
mirrored devices. You must specify an even number of
devices, of which there must be at least four. For example:
mkfs.btrfs -d raid10 -m raid10 /dev/sdf \
/dev/sdg /dev/sdh /dev/sdi /dev/sdj /dev/
sdk
When you want to mount the file system, you can specify it by any of its component devices, for example:
# mkfs.btrfs -d raid10 -m raid10 /dev/sd[fghijk]
# mount /dev/sdf /raid10_mountpoint
To find out the RAID configuration of a mounted btrfs file system, use this command:
200
Modifying a Btrfs File System
# btrfs filesystem df mountpoint
Note
The btrfs filesystem df command displays more accurate information about
the space used by a btrfs file system than the df command does.
Use the following form of the btrfs command to display information about all the btrfs file systems on a
system:
# btrfs filesystem show
19.4 Modifying a Btrfs File System
The following table shows how you can use the btrfs command to add or remove devices, and to
rebalance the layout of the file system data and metadata across the devices.
Command
Description
btrfs device add device mountpoint
Add a device to the file system that is mounted on
the specified mount point. For example:
btrfs device add /dev/sdd /myfs
btrfs device delete device mountpoint
Remove a device from a mounted file system. For
example:
btrfs device delete /dev/sde /myfs
btrfs device delete missing mountpoint
Remove a failed device from the file system that is
mounted in degraded mode. For example:
btrfs device remove missing /myfs
To mount a file system in degraded mode, specify
the -o degraded option to the mount command.
For a RAID configuration, if the number of devices
would fall below the minimum number that are
required, you must add the replacement device
before removing the failed device.
btrfs filesystem balance mountpoint
After adding or removing devices, redistribute the
file system data and metadata across the available
devices.
19.5 Compressing and Defragmenting a Btrfs File System
You can compress a btrfs file system to increase its effective capacity, and you can defragment it to
increase I/O performance.
To enable compression of a btrfs file system, specify one of the following mount options:
Mount Option
Description
compress=lzo
Use LZO compression.
compress=zlib
Use zlib compression.
LZO offers a better compression ratio, while zlib offers faster compression.
201
Resizing a Btrfs File System
You can also compress a btrfs file system at the same time that you defragment it.
To defragment a btrfs file system, use the following command:
# btrfs filesystem defragment filesystem_name
To defragment a btrfs file system and compress it at the same time:
# btrfs filesystem defragment -c filesystem_name
You can also defragment, and optionally compress, individual file system objects, such as directories and
files, within a btrfs file system.
# btrfs filesystem defragment [-c] file_name ...
Note
You can set up automatic defragmentation by specifying the autodefrag option
when you mount the file system. However, automatic defragmentation is not
recommended for large databases or for images of virtual machines.
Defragmenting a file or a subvolume that has a copy-on-write copy results breaks
the link between the file and its copy. For example, if you defragment a subvolume
that has a snapshot, the disk usage by the subvolume and its snapshot will increase
because the snapshot is no longer a copy-on-write image of the subvolume.
19.6 Resizing a Btrfs File System
You can use the btrfs command to increase the size of a mounted btrfs file system if there is space on
the underlying devices to accommodate the change, or to decrease its size if the file system has sufficient
available free space. The command does not have any effect on the layout or size of the underlying
devices.
For example, to increase the size of /mybtrfs1 by 2 GB:
# btrfs filesystem resize +2g /mybtrfs1
Decrease the size of /mybtrfs2 by 4 GB:
# btrfs filesystem resize -4g /mybtrfs2
Set the size of /mybtrfs3 to 20 GB:
# btrfs filesystem resize 20g /mybtrfs3
19.7 Creating Subvolumes and Snapshots
The top level of a btrfs file system is a subvolume consisting of a named b-tree structure that contains
directories, files, and possibly further btrfs subvolumes that are themselves named b-trees that contain
directories and files, and so on. To create a subvolume, change directory to the position in the btrfs file
system where you want to create the subvolume and enter the following command:
# btrfs subvolume create subvolume_name
Snapshots are a type of subvolume that records the contents of their parent subvolumes at the time that
you took the snapshot. If you take a snapshot of a btrfs file system and do not write to it, the snapshot
records the state of the original file system and forms a stable image from which you can make a backup.
If you make a snapshot writable, you can treat it as a alternate version of the original file system. The copyon-write functionality of btrfs file system means that snapshots are quick to create, and consume very little
disk space initially.
202
Creating Subvolumes and Snapshots
Note
Taking snapshots of a subvolume is not a recursive process. If you create a
snapshot of a subvolume, every subvolume or snapshot that the subvolume
contains is mapped to an empty directory of the same name inside the snapshot.
The following table shows how to perform some common snapshot operations:
Command
Description
btrfs subvolume snapshot pathname
pathname/snapshot_path
Create a snapshot snapshot_path of a parent
subvolume or snapshot specified by pathname. For
example:
btrfs subvolume snapshot /mybtrfs /
mybtrfs/snapshot1
List the subvolumes or snapshots of a subvolume or
snapshot specified by pathname. For example:
btrfs subvolume list pathname
btrfs subvolume list /mybtrfs
Note
You can use this command
to determine the ID of a
subvolume or snapshot.
btrfs subvolume set-default ID pathname By default, mount the snapshot or subvolume
specified by its ID instead of the parent subvolume.
For example:
btrfs subvolume set-default 4 /mybtrfs
btrfs subvolume get-default pathname
Displays the ID of the default subvolume that is
mounted for the specified subvolume. For example:
btrfs subvolume get-default /mybtrfs
You can mount a btrfs subvolume as though it were a disk device. If you mount a snapshot instead of its
parent subvolume, you effectively roll back the state of the file system to the time that the snapshot was
taken. By default, the operating system mounts the parent btrfs volume, which has an ID of 0, unless you
use set-default to change the default subvolume. If you set a new default subvolume, the system will
mount that subvolume instead in future. You can override the default setting by specifying either of the
following mount options:
Mount Option
Description
subvolid=snapshot_ID
Mount the subvolume or snapshot specified by its subvolume
ID instead of the default subvolume.
subvol=pathname/snapshot_path
Mount the subvolume or snapshot specified by its pathname
instead of the default subvolume.
Note
The subvolume or snapshot must
be located in the root of the btrfs file
system.
203
Cloning Virtual Machine Images and Linux Containers
When you have rolled back a file system by mounting a snapshot, you can take snapshots of the snapshot
itself to record its state.
When you no longer require a subvolume or snapshot, use the following command to delete it:
# btrfs subvolume delete subvolume_path
Note
Deleting a subvolume deletes all subvolumes that are below it in the b-tree
hierarchy. For this reason, you cannot remove the topmost subvolume of a btrfs file
system, which has an ID of 0.
19.7.1 Cloning Virtual Machine Images and Linux Containers
You can use a btrfs file system to provide storage space for virtual machine images and Linux Containers.
The ability to quickly clone files and create snapshots of directory structures makes btrfs an ideal candidate
for this purpose. For details of how to use the snapshot feature of btrfs to implement Linux Containers, see
the Oracle Linux Administrator's Solutions Guide.
19.8 Using the Send/Receive Feature
Note
The send/receive feature requires that you boot the system using UEK R3.
The send operation compares two subvolumes and writes a description of how to convert one subvolume
(the parent subvolume) into the other (the sent subvolume). You would usually direct the output to a file for
later use or pipe it to a receive operation for immediate use.
The simplest form of the send operation writes a complete description of a subvolume:
# btrfs send [-v] [-f sent_file] ... subvol
You can specify multiple instances of the -v option to display increasing amounts of debugging output. The
-f option allows you to save the output to a file. Both of these options are implicit in the following usage
examples.
The following form of the send operation writes a complete description of how to convert one subvolume
into another:
# btrfs send -p parent_subvol sent_subvol
If a subvolume such as a snapshot of the parent volume, known as a clone source, will be available during
the receive operation from which some of the data can be recovered, you can specify the clone source to
reduce the size of the output file:
# btrfs send [-p parent_subvol] -c clone_src [-c clone_src] ... subvol
You can specify the -c option multiple times if there is more than one clone source. If you do not specify
the parent subvolume, btrfs chooses a suitable parent from the clone sources.
You use the receive operation to regenerate the sent subvolume at a specified path:
# btrfs receive [-f sent_file] mountpoint
204
Using Send/Receive to Implement Incremental Backups
19.8.1 Using Send/Receive to Implement Incremental Backups
The following procedure is a suggestion for setting up an incremental backup and restore process for a
subvolume.
1. Create a read-only snapshot of the subvolume to serve as an initial reference point for the backup:
# btrfs subvolume snapshot -r /vol /vol/backup_0
2. Run sync to ensure that the snapshot has been written to disk:
# sync
3. Create a subvolume or directory on a btrfs file system as a backup area to receive the snapshot, for
example, /backupvol.
4. Send the snapshot to /backupvol:
# btrfs send /vol/backup_0 | btrfs receive /backupvol
This command creates the subvolume /backupvol/backup_0.
Having created the reference backup, you can then create incremental backups as required.
5. To create an incremental backup:
a. Create a new snapshot of the subvolume:
# btrfs subvolume snapshot -r /vol /vol/backup_1
b. Run sync to ensure that the snapshot has been written to disk:
# sync
c. Send only the differences between the reference backup and the new backup to the backup area:
# btrfs send -p /vol/backup_0 /vol/backup_1 | btrfs receive /backupvol
This command creates the subvolume /backupvol/backup_1.
19.9 Using Quota Groups
Note
The quota groups feature requires that you boot the system using UEK R3.
To enable quotas, use the following command on a newly created btrfs file system before any creating any
subvolumes:
# btrfs quota enable volume
To assign a quota-group limit to a subvolume, use the following command:
# btrfs qgroup limit size /volume/subvolume
For example:
# btrfs qgroup limit 1g /myvol/subvol1
# btrfs qgroup limit 512m /myvol/subvol2
205
Replacing Devices on a Live File System
To find out the quota usage for a subvolume, use the btrfs qgroup show path command:
19.10 Replacing Devices on a Live File System
Note
The device replacement feature requires that you boot the system using UEK R3.
You can replace devices on a live file system. You do not need to unmount the file system or stop any
tasks that are using it. If the system crashes or loses power while the replacement is taking place, the
operation resumes when the system next mounts the file system.
Use the following command to replace a device on a mounted btrfs file system:
# btrfs replace start source_dev target_dev [-r] mountpoint
source_dev and target_dev specify the device to be replaced (source device) and the replacement
device (target device). mountpoint specifies the file system that is using the source device. The target
device must be the same size as or larger than the source device. If the source device is no longer
available or you specify the -r option, the data is reconstructed by using redundant data obtained from
other devices (such as another available mirror). The source device is removed from the file system when
the operation is complete.
You can use the btrfs replace status mountpoint and btrfs replace cancel mountpoint
commands to check the progress of the replacement operation or to cancel the operation.
19.11 Creating Snapshots of Files
You can use the --reflink option to the cp command to create lightweight copies of a file within the
same subvolume of a btrfs file system. The copy-on-write mechanism saves disk space and allows copy
operations to be almost instantaneous. The btrfs file system creates a new inode that shares the same
disk blocks as the existing file, rather than creating a complete copy of the file's data or creating a link that
points to the file's inode. The resulting file appears to be a copy of the original file, but the original data
blocks are not duplicated. If you subsequently write to one of the files, the btrfs file system makes copies of
the blocks before they are written to, preserving the other file's content.
For example, the following command creates the snapshot bar of the file foo:
# cp -reflink foo bar
19.12 Converting an Ext2, Ext3, or Ext4 File System to a Btrfs File
System
You can use the btrfs-convert utility to convert an ext2, ext3, or ext4 file system to btrfs. The
utility preserves an image of the original file system in a snapshot named ext2_saved. This snapshot
allows you to roll back the conversion, even if you have made changes to the btrfs file system.
If you convert the root file system to btrfs, you can use snapshots to roll back changes such as upgrades
that you have made to the file system.
Note
You cannot convert a bootable partition, such as /boot, to a btrfs file system.
206
Converting a Non-root File System
19.12.1 Converting a Non-root File System
Caution
Before performing a file system conversion, make a backup of the file system from
which you can restore its state.
To convert an ext2, ext3, or ext4 file system other than the root file system to btrfs:
1. Unmount the file system.
# umount mountpoint
2. Run the correct version of fsck (for example, fsck.ext4) on the underlying device to check and
correct the integrity of file system.
# fsck.extN -f device
3. Convert the file system to a btrfs file system.
# btrfs-convert device
4. Edit the file /etc/fstab, and change the file system type of the file system to btrfs, for example:
/dev/sdb
/myfs
btrfs
defaults
0 0
5. Mount the converted file system on the old mount point.
# mount device mountpoint
19.12.2 Converting the root File System
Caution
Before performing a root file system conversion, make a full system backup from
which you can restore its state.
To convert an ext2, ext3, or ext4 root file system to btrfs:
1. Run the mount command to determine the device that is currently mounted as the root file system, and
the type of the file system.
In the following example, the root file system is configured as an LVM logical volume lv_root in the
volume group vg_hostol6, and the file system type is ext4. Using the ls -l command confirms
that the mapped device corresponds to /dev/vg_hostol6/lv_root.
# mount
...
/dev/mapper/vg_hostol6-lv_root on / type ext4 (rw)
...
# ls -l /dev/mapper/vg_hostol6-lv_root
lrwxrwxrwx. 1 root root 7 Sep 14 14:00 /dev/mapper/vg_hostol6-lv_root -> ../dm-0
# ls -l /dev/vg_hostol6/lv_root
lrwxrwxrwx. 1 root root 7 Sep 14 14:00 /dev/vg_hostol6/lv_root -> ../dm-0
In the next example, the root file system corresponds to the disk partition /dev/sda2:
# mount
...
/dev/sda2 on / type ext4 (rw)
...
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Converting the root File System
2. Shut down the system.
3. Boot the system from an Oracle Linux 6 Update 3 or later UEK Boot ISO (which you can burn to CD or
DVD if necessary). You can download the UEK Boot ISO from https://edelivery.oracle.com/linux.
Note
You must use the UEK Boot ISO. You cannot use the RHCK Boot ISO to
perform the conversion.
4. From the installation menu, select Rescue Installed System. When prompted, choose a language
and keyboard, select Local CD/DVD as the installation media, select No to bypass starting the network
interface, and select Skip to bypass selecting a rescue environment.
5. Select Start shell to obtain a bash shell prompt (bash-4.1#) at the bottom of the screen.
6. If the existing root file system is configured as an LVM volume, use the following command to start the
volume group (for example, vg_hostol6):
bash-4.1# lvchange -ay vg_hostol6
7. Run the correct version of fsck (for example, fsck.ext3 or fsck.ext4) to check and correct the
integrity of the file system.
bash-4.1# fsck.extN -f device
where device is the root file system device (for example, /dev/vg_hostol6/lv_root or /dev/
sda2).
8. Convert the file system to a btrfs file system.
bash-4.1# btrfs-convert device
9. Create a mount point (/mnt1) and mount the converted root file system on it.
bash-4.1# mkdir /mnt1
bash-4.1# mount -t btrfs device /mnt1
10. Use the vi command to edit the file /mnt1/etc/fstab, and change the file system type of the root
file system to btrfs, for example:
/dev/mapper/vg_hostol6-lv_root
/
btrfs
defaults
1 1
11. Create the file .autorelabel in the root of the mounted file system.
bash-4.1# touch /mnt1/.autorelabel
The presence of the .autorelabel file in / instructs SELinux to recreate the security attributes of all
files on the file system.
Note
If you do not create the .autorelabel file, you might not be able to boot
the system successfully. If you forget to create the file and the reboot fails,
either disable SELinux temporarily by specifying selinux=0 to the kernel boot
parameters, or run SELinux in permissive mode by specifying enforcing=0.
12. Unmount the converted root file system.
bash-4.1# umount /mnt1
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Mounting the Image of the Original File System
13. Remove the boot CD, DVD, or ISO, and reboot the system.
19.12.3 Mounting the Image of the Original File System
To mount the image of the original file system read-only:
1. Mount the snapshot of the original file system on a temporary mount point.
# mount -t btrfs -o subvol=ext2_saved device temp_mountpoint1
2. Mount the image of the original file system read-only on another temporary mount point, specifying the
correct file system type (ext2, ext3, or ext4) to the -t option.
# mount -t extN -o loop,ro temp_mountpoint1/image temp_mountpoint2
19.12.4 Deleting the Snapshot of the Original File System
Caution
If you delete the snapshot of the original file system to save storage space, you will
no longer be able to recover the original file system.
To delete the snapshot of the original file system and recover the space that it uses:
1. Delete the ext2_saved subvolume.
# btrfs subvolume delete mountpoint/ext2_saved
For example, if you converted the root file system (/) file system, you would enter:
# btrfs subvolume delete //ext2_saved
For another file system, such as /usr, you would enter:
# btrfs subvolume delete /usr/ext2_saved
2. Rebalance the btrfs file system.
# btrfs filesystem balance device
19.12.5 Recovering an Original Non-root File System
Caution
If you roll back a conversion, you will lose any changes that you have made to the
btrfs file system. Make a back up of the changes that you want to reapply to the
restored file system.
To roll back the conversion of the file system and recover the original file system:
1. Unmount the btrfs file system and all of its snapshots and images in the reverse order from which you
originally mounted them.
# umount temp_mountpoint2
# umount temp_mountpoint1/image
# umount mountpoint
2. Roll back the conversion.
# btrfs-convert -r device
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Installing a Btrfs root File System
3. Mount the original file system.
# mount -t extN device mountpoint
19.13 Installing a Btrfs root File System
For compatibility reasons, the default installation image of Oracle Linux boots the Red Hat compatible
kernel to perform the installation. Oracle provides an alternative installation image (UEK Boot ISO) that
supports the installation of Oracle Linux 6 Update 3 or later using the Unbreakable Enterprise Kernel (UEK)
as the installation kernel. This installation method allows you to create a btrfs root file system.
As the UEK Boot ISO contains only the bootable installation image, you must set up a network installation
server for the RPM packages. This server must have sufficient storage space to host the full Oracle Linux
Release 6 Update 3 or later Media Pack DVD image (approximately 3.5 GB), and you must configure it to
serve the image files using either NFS or HTTP to the target system on which you want to install Oracle
Linux 6 Update 3 or later.
• Section 19.13.1, “Setting up a New NFS Server”
• Section 19.13.2, “Configuring an Existing NFS Server”
• Section 19.13.3, “Setting up a New HTTP Server”
• Section 19.13.4, “Configuring an Existing HTTP Server”
• Section 19.13.5, “Setting up a Network Installation Server”
• Section 19.13.6, “Installing from a Network Installation Server”
19.13.1 Setting up a New NFS Server
Note
This procedure assumes that you are setting up an Oracle Linux 6 system as an
NFSv4 server. Using NFSv4 greatly simplifies firewall configuration as you need
only configure a single rule for TCP port 2049.
To set up an NFS server:
1. Install the nfs-utils package.
# yum install nfs-utils
2. Create the directory where you will copy the full Oracle Linux Release 6 Media Pack DVD image, for
example /var/OSimage/OL6.5:
# mkdir -p /var/OSimage/OL6.5
3. Edit the configuration file, /etc/exports, as follows.
a. Add an entry for the directory where you will copy the DVD image.
The following example allows read-only access to the directory /var/OSimage/OL6.5 for any
NFS client on the 192.168.1 subnet:
/var/OSimage/OL6.5 192.168.1.0/24(ro)
b. Save your changes to the file.
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Configuring an Existing NFS Server
4. Start the NFS server, and configure it to start after a reboot.
#
#
#
#
#
#
service rpcbind start
service nfs start
service nfslock start
chkconfig rpcbind on
chkconfig nfs on
chkconfig nfslock on
5. If you have configured a firewall on your system, configure it to allow incoming NFSv4 requests from
NFS clients.
For example, use the following commands to configure iptables to allow NFSv4 connections and
save the change to the firewall configuration:
# iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 2049 -j ACCEPT
# service iptables save
19.13.2 Configuring an Existing NFS Server
To configure an existing NFS server:
1. Create the directory where you will copy the full Oracle Linux Release 6 Media Pack DVD image, for
example /var/OSimage/OL6.5:
# mkdir -p /var/OSimage/OL6.5
2. Use the exportfs command to export the directory.
# exportfs -i -o options client:export_dir
For example, to allow read-only access to the directory /var/OSimage/OL6.5 for any NFS client on
the 192.168.1 subnet:
# exportfs -i -o ro 192.168.1.0/24:/var/OSimage/OL6.5
19.13.3 Setting up a New HTTP Server
Note
These instructions assume that you are setting up an Oracle Linux 6 system as an
Apache HTTP server.
To set up an HTTP server:
1. Install the Apache HTTP server package.
# yum install httpd
2. Create the directory where you will copy the full Oracle Linux Release 6 Media Pack DVD image, for
example /var/www/html/OSimage/OL6.5:
# mkdir -p /var/www/html/OSimage/OL6.5
Note
If SELinux is enabled in enforcing mode on your system, create the
directory under the /var/www/html directory hierarchy so that the
httpd_sys_content_t file type is set automatically on all the files in the
repository.
211
Configuring an Existing HTTP Server
3. Edit the HTTP server configuration file, /etc/httpd/conf/httpd.conf, as follows:
a. Specify the resolvable domain name of the server in the argument to ServerName.
ServerName server_addr:80
If the server does not have a resolvable domain name, enter its IP address instead. For example,
the following entry would be appropriate for an HTTP server with the IP address 192.168.1.100.
ServerName 192.168.1.100:80
b. If the directory to which you will copy the DVD image in not under /var/www/html, change the
default setting of DocumentRoot.
In this example, the DVD image will be copied to /var/www/html/OSimage/OL6.5 so the setting
of DocumentRoot can remain unchanged.
DocumentRoot "/var/www/html"
c. Verify that the <Directory> setting points to the same setting as DocumentRoot.
#
# This should be changed to whatever you set DocumentRoot to.
#
<Directory "/var/www/html">
d. If you want to be able to browse the directory hierarchy, verify that the Options directive specifies
the Indexes option, for example:
Options Indexes FollowSymLinks
Note
The Indexes option is not required for installation.
e. Save your changes to the file.
4. Start the Apache HTTP server, and configure it to start after a reboot.
# service httpd start
# chkconfig httpd on
5. If you have enabled a firewall on your system, configure it to allow incoming HTTP connection requests
on TCP port 80.
For example, the following command configures iptables to allow incoming HTTP connection
requests and saves the change to the firewall configuration:
# iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
# service iptables save
19.13.4 Configuring an Existing HTTP Server
To configure an existing Apache HTTP server:
1. Under the DocumentRoot hierarchy that is defined in the HTTP server configuration file (/etc/
httpd/conf/httpd.conf), create the directory where you will copy the full Oracle Linux Release 6
Media Pack DVD image, for example /var/www/html/OSimage/OL6.5:
# mkdir -p /var/www/html/OSimage/OL6.5
212
Setting up a Network Installation Server
2. Edit the HTTP server configuration file, /etc/httpd/conf/httpd.conf, and add a <Directory>
section, for example:
<Directory "/var/www/html/OSimage/OL6.5">
Options Indexes FollowSymLinks
AllowOverride None
Order allow,deny
Allow from all
</Directory>
Place this section after the closing </Directory> statement for the <Directory DocumentRoot>
section.
Note
The Indexes option is not required for installation. Specify this option if you
want to be able to browse the directory hierarchy.
19.13.5 Setting up a Network Installation Server
Note
This procedure assumes that you have set up the system as an NFS or HTTP
server.
To set up a network installation server:
1. Download the full Oracle Linux Media Pack DVD image (for example, V41362-01.iso for x86_64
(64 bit) Oracle Linux Release 6 Update 5) from the Oracle Software Delivery Cloud at http://
edelivery.oracle.com/linux.
2. Mount the DVD image on a suitable mount point (for example, /mnt):
# mount -t iso9660 -o loop V41362-01.iso mount_dir
3. Use the following command to extract the contents of the DVD image into a directory (output_dir)
whose contents are shareable using NFS or HTTP:
# cp -a -T mount_dir output_dir
For example, to copy the DVD image mounted on /mnt to /var/OSimage/OL6.5:
# cp -a -T /mnt /var/OSimage/OL6.5
or to /var/www/html/OSimage/OL6.5:
# cp -a -T /mnt /var/www/html/OSimage/OL6.5
4. Unmount the DVD image:
# umount mount_dir
5. Download the UEK Boot ISO image for the desired architecture (for example, V41364-01.iso for
x86_64 (64 bit)).
6. Mount the UEK Boot ISO image:
# mount -t iso9660 -o loop V41364-01.iso
7. Replace the contents of the images directory that you copied from the DVD image with the contents of
the images directory from the UEK Boot ISO image:
213
Installing from a Network Installation Server
# rm -rf output_dir/images
# cp -r mount_dir/images output_dir
For example, to replace /var/OSimage/OL6.5/images:
# rm -rf /var/OSimage/OL6.5/images
# cp -r /mnt/images /var/OSimage/OL6.5
or to replace /var/www/html/OSimage/OL6.5/images:
# rm -rf /var/www/html/OSimage/OL6.5/images
# cp -r /mnt/images /var/www/html/OSimage/OL6.5
8. If SELinux is enabled in enforcing mode on your system and you have configured the system as an
HTTP server but you did not copy the DVD image to a directory under /var/www/html:
a. Use the semanage command to define the default file type of the directory hierarchy as
httpd_sys_content_t:
# /usr/sbin/semanage fcontext -a -t httpd_sys_content_t "/var/OSimage(/.*)?"
b. Use the restorecon command to apply the file type to the entire directory hierarchy.
# /sbin/restorecon -R -v /var/OSimage
Note
The semanage and restorecon commands are provided by the
policycoreutils-python and policycoreutils packages.
9. Copy the UEK Boot ISO image to a suitable medium from which you can boot the target system on
which you want to install Oracle Linux 6 Update 5.
10. Unmount the UEK Boot ISO image:
# umount mount_dir
19.13.6 Installing from a Network Installation Server
To install a target system from a network installation server:
1. Boot the target system using the UEK Boot ISO.
2. Select Install or upgrade an existing system, press Tab, and enter askmethod as an additional
parameter on the boot command line:
> vmlinuz initrd=initrd.img askmethod
3. On the Installation Method screen, select either NFS directory or URL depending on whether you
configured your installation server to use NFS or HTTP respectively.
4. After configuring the network settings, enter the settings for the NFS or HTTP installation server.
For installation using NFS, enter the path of the full DVD image, for example /var/OSimage/OL6.5.
For installation using HTTP, enter the URL of the full DVD image, for example
http://192.168.1.100/OSimage/OL6.5.
5. The default disk layout creates a btrfs root file system.
214
About the Installation root File System
Note
You cannot configure a bootable partition, such as /boot, as a btrfs file system.
19.13.7 About the Installation root File System
The mounted root file system is a snapshot (named install) of the root file system taken at the end of
installation. To find out the ID of the parent of the root file system subvolume, use the following command:
# btrfs subvolume list /
ID 258 top level 5 path install
In this example, the installation root file system subvolume has an ID of 5. The subvolume with ID 258
(install) is currently mounted as /. Figure 19.1, “Layout of the root File System Following Installation”
illustrates the layout of the file system:
Figure 19.1 Layout of the root File System Following Installation
The top-level subvolume with ID 5 records the contents of the root file system file system at the end of
installation. The default subvolume (install) with ID 258 is currently mounted as the active root file
system.
The mount command shows the device that is currently mounted as the root file system:
# mount
/dev/mapper/vg_btrfs-lv_root on / type btrfs (rw)
...
To mount the installation root file system volume, you can use the following commands:
# mkdir /instroot
# mount -o subvolid=5 /dev/mapper/vg_btrfs-lv_root /instroot
If you list the contents of /instroot, you can see both the contents of the installation root file system
volume and the install snapshot, for example:
# ls /instroot
bin
cgroup etc
boot dev
home
install
lib
lib64
media
misc
mnt
net
opt
215
proc
root
sbin
selinux
srv
sys
tmp
usr
var
Creating Snapshots of the root File System
The contents of / and /instroot/install are identical as demonstrated in the following example
where a file (foo) created in /instroot/install is also visible in /:
# touch /instroot/install/foo
# ls /
bin
cgroup etc home
lib
boot dev
foo instroot lib64
# ls /instroot/install
bin
cgroup etc home
lib
boot dev
foo instroot lib64
# rm -f /foo
# ls /
bin
cgroup etc
instroot lib64
boot dev
home lib
media
# ls /instroot/install
bin
cgroup etc
instroot lib64
boot dev
home lib
media
media
misc
mnt
net
opt
proc
root
sbin
selinux
srv
sys
tmp
usr
var
media
misc
mnt
net
opt
proc
root
sbin
selinux
srv
sys
tmp
usr
var
misc
mnt
net
opt
proc
root
sbin
selinux
srv
sys
tmp
usr
var
misc
mnt
net
opt
proc
root
sbin
selinux
srv
sys
tmp
usr
var
19.13.8 Creating Snapshots of the root File System
To take a snapshot of the current root file system:
1. Mount the top level of the root file system on a suitable mount point.
# mount -o subvolid=5 /dev/mapper/vg_btrfs-lv_root /mnt
2. Change directory to the mount point and take the snapshot. In this example, the install subvolume
is currently mounted as the root file system system.
# cd /mnt
# btrfs subvolume snapshot install root_snapshot_1
Create a snapshot of 'install' in './root_snapshot_1'
3. Change directory to / and unmount the top level of the file system.
# cd /
# umount /mnt
The list of subvolumes now includes the newly created snapshot.
# btrfs subvolume list /
ID 258 top level 5 path install
ID 260 top level 5 path root_snapshot_1
19.13.9 Mounting Alternate Snapshots as the root File System
If you want to roll back changes to your system, you can mount a snapshot as the root file system by
specifying its ID as the default subvolume, for example:
# btrfs subvolume set-default 260 /
Reboot the system for the change to take effect.
19.13.10 Deleting Snapshots of the root File System
To delete a snapshot:
1. Mount the top level of the file system, for example:
# mount -o subvolid=5 /dev/mapper/vg_btrfs-lv_root /mnt
2. Change directory to the mount point and delete the snapshot.
216
Converting a Non-root Ext2 File System to Ext3
# cd /mnt
# btrfs subvolume delete install
Delete subvolume '/mnt/install'
3. Change directory to / and unmount the top level of the file system.
# cd /
# umount /mnt
The list of subvolumes now does not include install.
# btrfs subvolume list /
ID 260 top level 5 path root_snapshot_1
19.14 Converting a Non-root Ext2 File System to Ext3
Caution
Before performing a file system conversion, make a backup of the file system from
which you can restore its state.
To convert a non-root ext2 file system to ext3:
1. Unmount the ext2 file system:
# umount filesystem
2. Use fsck.ext2 to check the file system.
bash-4.1# fsck.ext2 -f device
3. Use the following command with the block device corresponding to the ext2 file system:
# tune2fs -j device
The command adds an ext3 journal inode to the file system.
4. Use fsck.ext3 to check the file system.
bash-4.1# fsck.ext3 -f device
5. Correct any entry for the file system in /etc/fstab so that its type is defined as ext3 instead of
ext2.
6. You can now remount the file system whenever convenient:
# mount filesystem
For more information, see the tune2fs(8) manual page.
19.15 Converting a root Ext2 File System to Ext3
Caution
Before performing a root file system conversion, make a full system backup from
which you can restore its state.
To convert a root ext2 file system to ext3:
1. Use the following command with the block device corresponding to the root file system:
217
Converting a root Ext2 File System to Ext3
# tune2fs -j device
The command adds an ext3 journal to the file system as the file /.journal.
2. Run the mount command to determine the device that is currently mounted as the root file system.
In the following example, the root file system corresponds to the disk partition /dev/sda2:
# mount
/dev/sda2 on / type ext2 (rw)
3. Shut down the system.
4. Boot the system from an Oracle Linux boot CD, DVD or ISO. You can download the ISO from https://
edelivery.oracle.com/linux.
5. From the installation menu, select Rescue Installed System. When prompted, choose a language
and keyboard, select Local CD/DVD as the installation media, select No to bypass starting the network
interface, and select Skip to bypass selecting a rescue environment.
6. Select Start shell to obtain a bash shell prompt (bash-4.1#) at the bottom of the screen.
7. If the existing root file system is configured as an LVM volume, use the following command to start the
volume group (for example, vg_host01):
bash-4.1# lvchange -ay vg_host01
8. Use fsck.ext3 to check the file system.
bash-4.1# fsck.ext3 -f device
where device is the root file system device (for example, /dev/sda2).
The command moves the .journal file to the journal inode.
9. Create a mount point (/mnt1) and mount the converted root file system on it.
bash-4.1# mkdir /mnt1
bash-4.1# mount -t ext3 device /mnt1
10. Use the vi command to edit /mnt1/etc/fstab, and change the file system type of the root file
system to ext3, for example:
/dev/sda2
/
ext3
defaults
1 1
11. Create the file .autorelabel in the root of the mounted file system.
bash-4.1# touch /mnt1/.autorelabel
The presence of the .autorelabel file in / instructs SELinux to recreate the security attributes of all
files on the file system.
Note
If you do not create the .autorelabel file, you might not be able to boot
the system successfully. If you forget to create the file and the reboot fails,
either disable SELinux temporarily by specifying selinux=0 to the kernel boot
parameters, or run SELinux in permissive mode by specifying enforcing=0.
12. Unmount the converted root file system.
218
Creating a Local OCFS2 File System
bash-4.1# umount /mnt1
13. Remove the boot CD, DVD, or ISO, and reboot the system.
For more information, see the tune2fs(8) manual page.
19.16 Creating a Local OCFS2 File System
To create an OCFS2 file system that will be locally mounted and not associated with a cluster, use the
following command:
# mkfs.ocfs2 -M local --fs-features=local -N 1 [options] device
For example, create a locally mountable OCFS2 volume on /dev/sdc1 with one node slot and the label
localvol:
# mkfs.ocfs2 -M local --fs-features=local -N 1 -L "localvol" /dev/sdc1
You can use the tunefs.ocfs2 utility to convert a local OCTFS2 file system to cluster use, for example:
# umount /dev/sdc1
# tunefs.ocfs2 -M cluster --fs-features=cluster -N 8 /dev/sdc1
This example also increases the number of node slots from 1 to 8 to allow up to eight nodes to mount the
file system.
19.17 About the XFS File System
Note
You must have an Oracle Linux Premier Support account to obtain technical
support for XFS with Oracle Linux.
The XFS file system is supported for the Unbreakable Enterprise Kernel Release 2
(2.6.39) and the Unbreakable Enterprise Kernel Release 3 (3.8.13) on the x86_64
architecture only.
XFS is a high-performance journaling file system that was initially created by Silicon Graphics, Inc. for
the IRIX operating system and later ported to Linux. The parallel I/O performance of XFS provides high
scalability for I/O threads, file system bandwidth, file and file system size, even when the file system spans
many storage devices.
A typical use case for XFS is to implement a several-hundred terabyte file system across multiple storage
servers, each server consisting of multiple FC-connected disk arrays.
XFS is not supported for use with the root (/) or boot file systems on Oracle Linux.
XFS has a large number of features that make it suitable for deployment in an enterprise-level computing
environment that requires the implementation of very large file systems:
• On x86_64 systems, XFS supports a maximum file system size and maximum file size of nearly 8 EB.
The maximum supported limit for XFS on Oracle Linux is 100 TB.
• XFS implements journaling for metadata operations, which guarantees the consistency of the file
system following loss of power or a system crash. XFS records file system updates asynchronously
to a circular buffer (the journal) before it can commit the actual data updates to disk. The journal can
be located either internally in the data section of the file system, or externally on a separate device to
reduce contention for disk access. If the system crashes or loses power, it reads the journal when the file
219
About External XFS Journals
system is remounted, and replays any pending metadata operations to ensure the consistency of the file
system. The speed of this recovery does not depend on the size of the file system.
• XFS is internally partitioned into allocation groups, which are virtual storage regions of fixed size. Any
files and directories that you create can span multiple allocation groups. Each allocation group manages
its own set of inodes and free space independently of other allocation groups to provide both scalability
and parallelism of I/O operations. If the file system spans many physical devices, allocation groups
can optimize throughput by taking advantage of the underlying separation of channels to the storage
components.
• XFS is an extent-based file system. To reduce file fragmentation and file scattering, each file's blocks
can have variable length extents, where each extent consists of one or more contiguous blocks. XFS's
space allocation scheme is designed to efficiently locate free extents that it can use for file system
operations. XFS does not allocate storage to the holes in sparse files. If possible, the extent allocation
map for a file is stored in its inode. Large allocation maps are stored in a data structure maintained by
the allocation group.
• To maximize throughput for XFS file systems that you create on an underlying striped, software or
hardware-based array, you can use the su and sw arguments to the -d option of the mkfs.xfs
command to specify the size of each stripe unit and the number of units per stripe. XFS uses the
information to align data, inodes, and journal appropriately for the storage. On lvm and md volumes and
some hardware RAID configurations, XFS can automatically select the optimal stripe parameters for you.
• To reduce fragmentation and increase performance, XFS implements delayed allocation, reserving file
system blocks for data in the buffer cache, and allocating the block when the operating system flushes
that data to disk.
• XFS supports extended attributes for files, where the size of each attribute's value can be up to 64 KB,
and each attribute can be allocated to either a root or a user name space.
• Direct I/O in XFS implements high throughput, non-cached I/O by performing DMA directly between an
application and a storage device, utilising the full I/O bandwidth of the device.
• To support the snapshot facilities that volume managers, hardware subsystems, and databases provide,
you can use the xfs_freeze command to suspend and resume I/O for an XFS file system. See
Section 19.22, “Freezing and Unfreezing an XFS File System”.
• To defragment individual files in an active XFS file system, you can use the xfs_fsr command. See
Section 19.25, “Defragmenting an XFS File System”.
• To grow an XFS file system, you can use the xfs_growfs command. See Section 19.21, “Growing an
XFS File System”.
• To back up and restore a live XFS file system, you can use the xfsdump and xfsrestore commands.
See Section 19.24, “Backing up and Restoring XFS File Systems”.
• XFS supports user, group, and project disk quotas on block and inode usage that are initialized when
the file system is mounted. Project disk quotas allow you to set limits for individual directory hierarchies
within an XFS file system without regard to which user or group has write access to that directory
hierarchy.
You can find more information about XFS at http://xfs.org/index.php/XFS_Papers_and_Documentation.
19.17.1 About External XFS Journals
The default location for an XFS journal is on the same block device as the data. As synchronous metadata
writes to the journal must complete successfully before any associated data writes can start, such a
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About XFS Write Barriers
layout can lead to disk contention for the typical workload pattern on a database server. To overcome
this problem, you can place the journal on a separate physical device with a low-latency I/O path. As the
journal typically requires very little storage space, such an arrangement can significantly improve the file
system's I/O throughput. A suitable host device for the journal is a solid-state drive (SSD) device or a RAID
device with a battery-backed write-back cache.
To reserve an external journal with a specified size when you create an XFS file system, specify the l logdev=device,size=size option to the mkfs.xfs command. If you omit the size parameter,
mkfs.xfs selects a journal size based on the size of the file system. To mount the XFS file system so that
it uses the external journal, specify the -o logdev=device option to the mount command.
19.17.2 About XFS Write Barriers
A write barrier assures file system consistency on storage hardware that supports flushing of in-memory
data to the underlying device. This ability is particularly important for write operations to an XFS journal that
is held on a device with a volatile write-back cache.
By default, an XFS file system is mounted with a write barrier. If you create an XFS file system on a LUN
that has a battery-backed, non-volatile cache, using a write barrier degrades I/O performance by requiring
data to be flushed more often than necessary. In such cases, you can remove the write barrier by mounting
the file system with the -o nobarrier option to the mount command.
19.17.3 About Lazy Counters
With lazy-counters enabled on an XFS file system, the free-space and inode counters are maintained
in parts of the file system other than the superblock. This arrangement can significantly improve I/O
performance for application workloads that are metadata intensive.
Lazy counters are enabled by default, but if required, you can disable them by specifying the -l lazycount=0 option to the mkfs.xfs command.
19.18 Installing the XFS Packages
Note
You can also obtain the XFS packages from Public Yum.
To install the XFS packages on a system:
1. Log in to ULN, and subscribe your system to the ol6_x86_64_latest channel.
2. On your system, use yum to install the xfsprogs and xfsdump packages:
# yum install xfsprogs xfsdump
3. If required, use yum to install the XFS development and QA packages:
# yum install xfsprogs-devel xfsprogs-qa-devel
19.19 Creating an XFS File System
You can use the mkfs.xfs command to create an XFS file system, for example.
# mkfs.xfs /dev/vg0/lv0
meta-data=/dev/vg0/lv0
isize=256
agcount=32, agsize=8473312 blks
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Modifying an XFS File System
=
=
=
naming
=version 2
log
=internal log
=
realtime =none
data
sectsz=512
bsize=4096
sunit=0
bsize=4096
bsize=4096
sectsz=512
extsz=4096
attr=2, projid32bit=0
blocks=271145984, imaxpct=25
swidth=0 blks
ascii-ci=0
blocks=32768, version=2
sunit=0 blks, lazy-count=1
blocks=0, rtextents=0
To create an XFS file system with a stripe-unit size of 32 KB and 6 units per stripe, you would specify the
su and sw arguments to the -d option, for example:
# mkfs.xfs -d su=32k,sw=6 /dev/vg0/lv1
For more information, see the mkfs.xfs(8) manual page.
19.20 Modifying an XFS File System
Note
You cannot modify a mounted XFS file system.
You can use the xfs_admin command to modify an unmounted XFS file system. For example, you can
enable or disable lazy counters, change the file system UUID, or change the file system label.
To display the existing label for an unmounted XFS file system and then apply a new label:
# xfs_admin
label = ""
# xfs_admin
writing all
new label =
-l /dev/sdb
-L "VideoRecords" /dev/sdb
SBs
"VideoRecords"
Note
The label can be a maximum of 12 characters in length.
To display the existing UUID and then generate a new UUID:
# xfs_admin -u /dev/sdb
UUID = cd4f1cc4-15d8-45f7-afa4-2ae87d1db2ed
# xfs_admin -U generate /dev/sdb
writing all SBs
new UUID = c1b9d5a2-f162-11cf-9ece-0020afc76f16
To clear the UUID altogether:
# xfs_admin -U nil /dev/sdb
Clearing log and setting UUID
writing all SBs
new UUID = 00000000-0000-0000-0000-000000000000
To disable and then re-enable lazy counters:
# xfs_admin -c 0 /dev/sdb
Disabling lazy-counters
# xfs_admin -c 1 /dev/sdb
Enabling lazy-counters
For more information, see the mkfs_admin(8) manual page.
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Growing an XFS File System
19.21 Growing an XFS File System
Note
You cannot grow an XFS file system that is currently unmounted.
There is currently no command to shrink an XFS file system.
You can use the xfs_growfs command to increase the size of a mounted XFS file system if there is
space on the underlying devices to accommodate the change. The command does not have any effect on
the layout or size of the underlying devices. If necessary, use the underlying volume manager to increase
the physical storage that is available. For example, you can use the vgextend command to increase the
storage that is available to an LVM volume group and lvextend to increase the size of the logical volume
that contains the file system.
You cannot use the parted command to resize a partition that contains an XFS file system. You must
instead recreate the partition with a larger size and restore its contents from a backup if you deleted the
original partition or from the contents of the original partition if you did not delete it to free up disk space.
For example, to increase the size of /myxfs1 to 4 TB, assuming a block size of 4 KB:
# xfs_growfs -D 1073741824 /myxfs1
To increase the size of the file system to the maximum size that the underlying device supports, specify the
-d option:
# xfs_growfs -d /myxfs1
For more information, see the xfs_growfs(8) manual page.
19.22 Freezing and Unfreezing an XFS File System
If you need to take a hardware-based snapshot of an XFS file system, you can temporarily stop write
operations to it.
Note
You do not need to explicitly suspend write operations if you use the lvcreate
command to take an LVM snapshot.
To freeze and unfreeze an XFS file system, use the -f and -u options with the xfs_freeze command,
for example:
# xfs_freeze -f /myxfs
# # ... Take snapshot of file system ...
# xfs_freeze -u /myxfs
Note
You can also use the xfs_freeze command with btrfs, ext3, and ext4 file
systems.
For more information, see the xfs_freeze(8) manual page.
19.23 Setting Quotas on an XFS File System
The following table shows the mount options that you can specify to enable quotas on an XFS file system:
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Setting Project Quotas
Mount Option
Description
gqnoenforce
Enable group quotas. Report usage, but do not enforce usage limits.
gquota
Enable group quotas and enforce usage limits.
pqnoenforce
Enable project quotas. Report usage, but do not enforce usage limits.
pquota
Enable project quotas and enforce usage limits.
uqnoenforce
Enable user quotas. Report usage, but do not enforce usage limits.
uquota
Enable user quotas and enforce usage limits.
To show the block usage limits and the current usage in the myxfs file system for all users, use the
xfs_quota command:
# xfs_quota -x -c 'report -h' /myxfs
User quota on /myxfs (/dev/vg0/lv0)
Blocks
User ID
Used
Soft
Hard Warn/Grace
---------- --------------------------------root
0
0
0 00 [------]
guest
0
200M
250M 00 [------]
The following forms of the command display the free and used counts for blocks and inodes respectively in
the manner of the df -h command:
# xfs_quota -c 'df -h' /myxfs
Filesystem
Size
Used Avail Use% Pathname
/dev/vg0/lv0 200.0G 32.2M 20.0G
1% /myxfs
# xfs_quota -c 'df -ih' /myxfs
Filesystem
Inodes
Used
Free Use% Pathname
/dev/vg0/lv0 21.0m
4 21.0m
1% /myxfs
If you specify the -x option to enter expert mode, you can use subcommands such as limit to set soft
and hard limits for block and inode usage by an individual user, for example:
# xfs_quota -x -c 'limit bsoft=200m bhard=250m isoft=200 ihard=250 guest' /myxfs
Of course, this command requires that you mounted the file system with user quotas enabled.
To set limits for a group on an XFS file system that you have mounted with group quotas enabled, specify
the -g option to limit, for example:
# xfs_quota -x -c 'limit -g bsoft=5g bhard=6g devgrp' /myxfs
For more information, see the xfs_quota(8) manual page.
19.23.1 Setting Project Quotas
User and group quotas are supported by other file systems, such as ext4. The XFS file system
additionally allows you to set quotas on individual directory hierarchies in the file system that are known
as managed trees. Each managed tree is uniquely identified by a project ID and an optional project name.
Being able to control the disk usage of a directory hierarchy is useful if you do not otherwise want to set
quota limits for a privileged user (for example, /var/log) or if many users or groups have write access to
a directory (for example, /var/tmp).
To define a project and set quota limits on it:
1. Mount the XFS file system with project quotas enabled:
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Backing up and Restoring XFS File Systems
# mount -o pquota device mountpoint
For example, to enable project quotas for the /myxfs file system:
# mount -o pquota /dev/vg0/lv0 /myxfs
2. Define a unique project ID for the directory hierarchy in the /etc/projects file:
# echo project_ID:mountpoint/directory >> /etc/projects
For example, to set a project ID of 51 for the directory hierarchy /myxfs/testdir:
# echo 51:/myxfs/testdir >> /etc/projects
3. Create an entry in the /etc/projid file that maps a project name to the project ID:
# echo project_name:project_ID >> /etc/projid
For example, to map the project name testproj to the project with ID 51:
# echo testproj:51 >> /etc/projid
4. Use the project subcommand of xfs_quota to define a managed tree in the XFS file system for the
project:
# xfs_quota -x -c ’project -s project_name’ mountpoint
For example, to define a managed tree in the /myxfs file system for the project testproj, which
corresponds to the directory hierarchy /myxfs/testdir:
# xfs_quota -x -c ’project -s testproj’ /myxfs
5. Use the limit subcommand to set limits on the disk usage of the project:
# xfs_quota -x -c ’limit -p arguments project_name’ mountpoint
For example, to set a hard limit of 10 GB of disk space for the project testproj:
# xfs_quota -x -c ’limit -p bhard=10g testproj’ /myxfs
For more information, see the projects(5), projid(5), and xfs_quota(8) manual pages.
19.24 Backing up and Restoring XFS File Systems
The xfsdump package contains the xfsdump and xfsrestore utilities. xfsdump examines the files
in an XFS file system, determines which files need to be backed up, and copies them to the storage
medium. Any backups that you create using xfsdump are portable between systems with different endian
architectures. xfsrestore restores a full or incremental backup of an XFS file system. You can also
restore individual files and directory hierarchies from backups.
Note
Unlike an LVM snapshot, which immediately creates a sparse clone of a volume,
xfsdump takes time to make a copy of the file system data.
You can use the xfsdump command to create a backup of an XFS file system on a device such as a tape
drive, or in a backup file on a different file system. A backup can span multiple physical media that are
written on the same device, and you can write multiple backups to the same medium. You can write only
a single backup to a file. The command does not overwrite existing XFS backups that it finds on physical
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Backing up and Restoring XFS File Systems
media. You must use the appropriate command to erase a physical medium if you need to overwrite any
existing backups.
For example, the following command writes a level 0 (base) backup of the XFS file system, /myxfs to the
device /dev/st0 and assigns a session label to the backup:
# xfsdump -l 0 -L "Backup level 0 of /myxfs `date`" -f /dev/st0 /myxfs
You can make incremental dumps relative to an existing backup by using the command:
# xfsdump -l level -L "Backup level level of /myxfs `date`" -f /dev/st0 /myxfs
A level 1 backup records only file system changes since the level 0 backup, a level 2 backup records only
the changes since the latest level 1 backup, and so on up to level 9.
If you interrupt a backup by typing Ctrl-C and you did not specify the -J option (suppress the dump
inventory) to xfsdump , you can resume the dump at a later date by specifying the -R option:
# xfsdump -R -l 1 -L "Backup level 1 of /myxfs `date`" -f /dev/st0 /myxfs
In this example, the backup session label from the earlier, interrupted session is overridden.
You use the xfsrestore command to find out information about the backups you have made of an XFS
file system or to restore data from a backup.
The xfsrestore -I command displays information about the available backups, including the session ID
and session label. If you want to restore a specific backup session from a backup medium, you can specify
either the session ID or the session label.
For example, to restore an XFS file system from a level 0 backup by specifying the session ID:
# xfsrestore -f /dev/st0 -S c76b3156-c37c-5b6e-7564-a0963ff8ca8f /myxfs
If you specify the -r option, you can cumulatively recover all data from a level 0 backup and the higherlevel backups that are based on that backup:
# xfsrestore -r -f /dev/st0 -v silent /myxfs
The command searches the archive looking for backups based on the level 0 backup, and prompts you to
choose whether you want to restore each backup in turn. After restoring the backup that you select, the
command exits. You must run this command multiple times, first selecting to restore the level 0 backup,
and then subsequent higher-level backups up to and including the most recent one that you require to
restore the file system data.
Note
After completing a cumulative restoration of an XFS file system, you should delete
the housekeeping directory that xfsrestore creates in the destination directory.
You can recover a selected file or subdirectory contents from the backup medium, as shown in the
following example, which recovers the contents of /myxfs/profile/examples to /tmp/profile/
examples from the backup with a specified session label:
# xfsrestore -f /dev/sr0 -L "Backup level 0 of /myxfs Sat Mar 2 14:47:59 GMT 2013" \
-s profile/examples /usr/tmp
Alternatively, you can interactively browse a backup by specifying the -i option:
# xfsrestore -f /dev/sr0 -i
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Defragmenting an XFS File System
This form of the command allows you browse a backup as though it were a file system. You can change
directories, list files, add files, delete files, or extract files from a backup.
To copy the entire contents of one XFS file system to another, you can combine xfsdump and
xfsrestore, using the -J option to suppress the usual dump inventory housekeeping that the commands
perform:
# xfsdump -J - /myxfs | xfsrestore -J - /myxfsclone
For more information, see the xfsdump(8) and xfsrestore(8) manual pages.
19.25 Defragmenting an XFS File System
You can use the xfs_fsr command to defragment whole XFS file systems or individual files within an
XFS file system. As XFS is an extent-based file system, it is usually unnecessary to defragment a whole
file system, and doing so is not recommended.
To defragment an individual file, specify the name of the file as the argument to xfs_fsr.
# xfs_fsr pathname
If you run the xfs_fsr command without any options, the command defragments all currently mounted,
writeable XFS file systems that are listed in /etc/mtab. For a period of two hours, the command
passes over each file system in turn, attempting to defragment the top ten percent of files that have
the greatest number of extents. After two hours, the command records its progress in the file /var/
tmp/.fsrlast_xfs, and it resumes from that point if you run the command again.
For more information, see the xfs_fsr(8) manual page.
19.26 Checking and Repairing an XFS File System
Note
If you have an Oracle Linux Premier Support account and encounter a problem
mounting an XFS file system, send a copy of the /var/log/messages file to
Oracle Support and wait for advice.
If you cannot mount an XFS file system, you can use the xfs_check command to check its consistency.
Usually, you would only run this command on the device file of an unmounted file system that you believe
has a problem. If xfs_check displays any output when you do not run it in verbose mode, the file system
has an inconsistency.
# xfscheck device
If you can mount the file system and you do not have a suitable backup, you can use xfsdump to attempt
to back up the existing file system data, However, the command might fail if the file system's metadata has
become too corrupted.
You can use the xfs_repair command to attempt to repair an XFS file system specified by its device
file. The command replays the journal log to fix any inconsistencies that might have resulted from the
file system not being cleanly unmounted. Unless the file system has an inconsistency, it is usually not
necessary to use the command, as the journal is replayed every time that you mount an XFS file system.
# xfs_repair device
If the journal log has become corrupted, you can reset the log by specifying the -L option to xfs_repair.
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Checking and Repairing an XFS File System
Warning
Resetting the log can leave the file system in an inconsistent state, resulting in data
loss and data corruption. Unless you are experienced in debugging and repairing
XFS file systems using xfs_db, it is recommended that you instead recreate the
file system and restore its contents from a backup.
If you cannot mount the file system or you do not have a suitable backup, running xfs_repair is the only
viable option unless you are experienced in using xfs_db.
xfs_db provides an internal command set that allows you to debug and repair an XFS file system
manually. The commands allow you to perform scans on the file system, and to navigate and display its
data structures. If you specify the -x option to enable expert mode, you can modify the data structures.
# xfs_db [-x] device
For more information, see the xfs_check(8), xfs_db(8) and xfs_repair(8) manual pages, and the
help command within xfs_db.
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Chapter 20 Shared File System Administration
Table of Contents
20.1 About Shared File Systems ..................................................................................................... 229
20.2 About NFS .............................................................................................................................. 229
20.2.1 Configuring an NFS Server ........................................................................................... 231
20.2.2 Mounting an NFS File System ...................................................................................... 234
20.3 About Samba .......................................................................................................................... 234
20.3.1 Configuring a Samba Server ......................................................................................... 234
20.3.2 About Samba Configuration for Windows Workgroups and Domains ............................... 236
20.3.3 Accessing Samba Shares from a Windows Client .......................................................... 239
20.3.4 Accessing Samba Shares from an Oracle Linux Client ................................................... 239
This chapter describes administration tasks for the NFS and Samba shared file systems.
20.1 About Shared File Systems
Oracle Linux supports the following shared file system types:
NFS
The Network File System (NFS) is a distributed file system that allows a client computer to access
files over a network as though the files were on local storage. See Section 20.2, “About NFS”.
Samba
Samba enables the provision of file and print services for Microsoft Windows clients and can
integrate with a Windows workgroup, NT4 domain, or Active Directory domain. See Section 20.3,
“About Samba”.
20.2 About NFS
A Network File System (NFS) server can share directory hierarchies in its local file systems with remote
client systems over an IP-based network. After an NFS server exports a directory, NFS clients mount this
directory if they have been granted permission to do so. The directory appears to the client systems as
if it were a local directory. NFS centralizes storage provisioning and can improves data consistency and
reliability.
Oracle Linux supports three versions of the NFS protocol:
• NFS version 2 (NFSv2), specified in RFC 1094.
• NFS version 3 (NFSv3), specified in RFC 1813.
• NFS version 4 (NFSv4), specified in RFC 3530.
NFSv2 and NFSv3 rely on Remote Procedure Call (RPC) services, which are controlled by the rpcbind
service. rpcbind responds to requests for an RPC service and sets up connections for the requested
service. In addition, separate lockd and rpc.statd services are used to handle locking and mounting
protocols. Configuring a firewall to cope with the various ranges of ports that are used by all these services
is complex and error prone.
NFSv4 does not use rpcbind as the NFS server itself listens on TCP port 2049 for service requests. The
mounting and locking protocols are also integrated into the NFSv4 protocol, so the lockd and rpc.statd
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About NFS
services are also not required. These refinements mean that firewall configuration for NFSv4 is no more
difficult than for a service such as HTTP.
The following table describes the various services that are used with versions 2, 3, and 4 of NFS:
Service
Used in Version
Description
lockd
2 and 3
Handles the RPC processes that allow NFS clients to obtain
locks on files on the server.
Started by the nfslock service.
nfs
2, 3, and 4
Starts all services that are required to implement shared NFS
file systems.
If only NFSv4 clients can access the server, this is the only
NFS service that needs to be started explicitly.
nfsd
2, 3, and 4
Implements the kernel-space part of the NFS service.
Started by the nfs service.
nfslock
2 and 3
Starts the RPC processes that allow NFS clients to lock files on
the server.
Start this service after the nfs service to support NFSv2 and
NFSv3 clients.
rpcbind
2 and 3
Responds to requests for an RPC service and sets up
connections for the requested service.
Start this service before the nfs service to support NFSv2 and
NFSv3 clients.
For more information, see the rpcbind(8) manual page.
rpc.gssd and
rpc.svcgssd
2,3, and 4
Implement the RPCSEC_GSS protocol, which provides
authentication only (krb5), integrity protection (krb5i), or
privacy protection (krb5p) security for protocols that use
RPC. Before a client can send any RPC requests, it must first
establish a security context with the server.
Started by the nfs service if cryptographic security is enabled.
For more information, see the exports(5), rpc.gssd(8),
and rpc.svcgssd(8) manual pages.
rpc.idmapd
4
Provides mapping between NFSv4 names (strings of the form
[email protected]) and local UIDs and GIDs, using definitions in /
etc/idmapd.conf.
Started by the nfs service.
For more information, see the idmapd.conf(5) and
rpc.idmapd(8) manual pages.
rpc.mountd
2,3, and 4
Handles mount requests from NFSv2 and NFSv3 clients by
checking that the NFS server exports the requested NFS share
and that the client is allowed to access it.
For NFSv4, this service is required only to set up exports.
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Configuring an NFS Server
Service
Used in Version
Description
Started by the nfs service.
For more information, see the rpc.mountd(8) manual page.
rpc.nfsd
2,3, and 4
Implements the user-space part of the NFS service, which
specifies on what sort of sockets the kernel service should
listen, what NFS versions it supports, and how many kernel
threads it should use. The number of threads is visible and
settable via /proc/fs/nfsd/threads.
Started by the nfs service.
For more information, see the rpc.nfsd(8) manual page.
rpc.rquotad
2,3, and 4
Provides quota information for the quota command to
display user quotas for remote file systems and the edquota
command to set quotas on remote file systems.
Started by the nfs service.
For more information, see the rpc.rquotad(8) manual
page.
rpc.statd
2 and 3
Implements the Network Status Monitor (NSM) RPC protocol,
which notifies NFS clients when an NFS server has restarted
after an uncontrolled shutdown or system crash.
Started by the nfslock service.
For more information, see the rpc.statd(8) manual page.
20.2.1 Configuring an NFS Server
To configure an NFS server:
1. Install the nfs-utils package:
# yum install nfs-utils
2. Edit the /etc/exports file to define the directories that the server will make available for clients to
mount, for example:
/var/folder 192.0.2.102(rw,async)
/usr/local/apps *(all_squash,anonuid=501,anongid=501,ro)
/var/projects/proj1 192.168.1.0/24(ro) mgmtpc(rw)
Each entry consists of the local path to the exported directory, followed by a list of clients that can
mount the directory with client-specific mount options in parentheses. If this example:
• The client system with the IP address 192.0.2.102 can mount /var/folder with read and write
permissions. All writes to the disk are asynchronous, which means that the server does not wait for
write requests to be written to disk before responding to further requests from the client.
• All clients can mount /usr/local/apps read-only, and all connecting users including root are
mapped to the local unprivileged user with UID 501 and GID 501.
• All clients on the 192.168.1.0 subnet can mount /var/projects/proj1 read-only, and the client
system named mgmtpc can mount the directory with read-write permissions.
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Configuring an NFS Server
Note
There is no space between a client specifier and the parenthesized list of
options.
For more information, see the exports(5) manual page.
3. If the server will serve NFSv2 and NFSv3 clients, start the rpcbind service, and configure the service
to start following a system reboot:
# service rpcbind start
# chkconfig rpcbind on
4. Start the nfs service, and configure the service to start following a system reboot:
# service nfs start
# chkconfig nfs on
5. If the server will serve NFSv2 and NFSv3 clients, start the nfslock service, and configure the service
to start following a system reboot:
# service nfslock start
# chkconfig nfslock on
6. If the server will serve NFSv4 clients, edit /etc/idmapd.conf and edit the definition for the Domain
parameter to specify the DNS domain name of the server, for example:
Domain = mydom.com
This setting prevents the owner and group being unexpectedly listed as the anonymous user or group
(nobody or nogroup) on NFS clients when the all_squash mount option has not been specified.
7. If you need to allow access through the firewall for NFSv4 clients only, use the following commands to
configure iptables to allow NFSv4 connections and save the change to the firewall configuration:
# iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 2049 -j ACCEPT
# service iptables save
This configuration assumes that rpc.nfsd listens for client requests on TCP port 2049.
8. If you need to allow access through the firewall for NFSv2 and NFSv3 clients as well as NFSv4 clients:
a. Stop the firewall service:
# service iptables stop
b. Edit /etc/sysconfig/nfs and create entries for the following port settings:
# TCP port rpc.lockd should listen on.
LOCKD_TCPPORT=32803
# UDP port rpc.lockd should listen on.
LOCKD_UDPPORT=32769
# Port rpc.mountd should listen on.
MOUNTD_PORT=892
# Port rpc.statd should listen on.
STATD_PORT=662
The port values shown in this example are the default settings that are commented-out in the file.
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Configuring an NFS Server
c. To verify that none of the ports specified in /etc/sysconfig/nfs is in use, enter the following
commands:
#
#
#
#
lsof
lsof
lsof
lsof
-i
-i
-i
-i
tcp:32803
udp:32769
:892
:662
If any port is in use, use the lsof -i command to determine an unused port and amend the
setting in /etc/sysconfig/nfs.
d. Stop and restart the nfslock and nfs services:
#
#
#
#
service
service
service
service
nfslock stop
nfs stop
nfs start
nfslock start
NFS fails to start if one of the specified ports is in use, and reports an error in /var/log/
messages. Edit /etc/sysconfig/nfs to use a different port number for the service that could
not start, and attempt to restart the nfslock and nfs services. You can use the rpcinfo -p
command to confirm on which ports RPC services are listening.
e. Restart the firewall service, configure iptables to allow NFSv2 and NFSv3 connections, and save
the change to the firewall configuration:
#
#
#
#
#
#
#
#
#
#
#
#
service iptables stop
iptables -I INPUT -p tcp
iptables -I INPUT -p udp
iptables -I INPUT -p tcp
iptables -I INPUT -p udp
iptables -I INPUT -p tcp
iptables -I INPUT -p udp
iptables -I INPUT -p tcp
iptables -I INPUT -p udp
iptables -I INPUT -p tcp
iptables -I INPUT -p udp
service iptables save
-m
-m
-m
-m
-m
-m
-m
-m
-m
-m
state --state NEW -m tcp --dport
udp --dport 2049 -j ACCEPT
state --state NEW -m tcp --dport
udp --dport 111 -j ACCEPT
state --state NEW -m tcp --dport
udp --dport 32769 -j ACCEPT
state --state NEW -m tcp --dport
udp --dport 892 -j ACCEPT
state --state NEW -m tcp --dport
udp --dport 662 -j ACCEPT
2049 -j ACCEPT
111 -j ACCEPT
32803 -j ACCEPT
892 -j ACCEPT
662 -j ACCEPT
The port values shown in this example assume that the default port settings in /etc/sysconfig/
nfs are available for use by RPC services. This configuration also assumes that rpc.nfsd and
rpcbind listen on ports 2049 and 111 respectively.
9. Use the showmount –e command to display a list of the exported file systems, for example:
# showmount –e
Export list for host01.mydom.com
/var/folder 192.0.2.102
/usr/local/apps *
/var/projects/proj1 192.168.1.0/24 mgmtpc
showmount -a lists the current clients and the file systems that they have mounted, for example:
# showmount –a
mgmtpc.mydom.com:/var/projects/proj1
Note
To be able to use the showmount command from NFSv4 clients,
MOUNTD_PORT must be defined in /etc/sysconfig/nfs and a firewall rule
must allow access on this TCP port.
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Mounting an NFS File System
If you want to export or unexport directories without editing /etc/exports and restarting the NFS
service, use the exportfs command. The following example makes /var/dev available with read and
write access by all clients, and ignores any existing entries in /etc/exports.
# exportfs -i -o ro *:/var/dev
For more information, see the exportfs(8), exports(5), and showmount(8) manual pages.
20.2.2 Mounting an NFS File System
To mount an NFS file system on a client:
1. Install the nfs-utils package:
# yum install nfs-utils
2. Use showmount -e to discover what file systems an NFS server exports, for example:
# showmount –e host01.mydom.com
Export list for host01.mydom.com
/var/folder 192.0.2.102
/usr/local/apps *
/var/projects/proj1 192.168.1.0/24 mgmtpc
3. Use the mount command to mount an exported NFS file system on an available mount point:
# mount -t nfs -o ro,nosuid host01.mydoc.com:/usr/local/apps /apps
This example mounts /usr/local/apps exported by host01.mydoc.com with read-only
permissions on /apps. The nosuid option prevents remote users from gaining higher privileges by
running a setuid program.
4. To configure the system to mount an NFS file system at boot time, add an entry for the file system to /
etc/fstab, for example:
host01.mydoc.com:/usr/local/apps
/apps
nfs
ro,nosuid
0 0
For more information, see the mount(8), nfs(5), and showmount(8) manual pages.
20.3 About Samba
Samba is an open-source implementation of the Server Message Block (SMB) protocol that allows Oracle
Linux to interoperate with Windows systems as both a server and a client. Samba can share Oracle Linux
files and printers with Windows systems, and it enables Oracle Linux users to access files on Windows
systems. Samba uses the NetBIOS over TCP/IP protocol that allows computer applications that depend on
the NetBIOS API to work on TCP/IP networks.
20.3.1 Configuring a Samba Server
To configure a Samba server:
1. Install the samba and samba-winbind packages:
# yum install samba samba-winbind
2. Edit /etc/samba/smb.conf and configure the sections to support the required services, for example:
[global]
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Configuring a Samba Server
security = ADS
realm = MYDOM.REALM
password server = krbsvr.mydom.com
load printers = yes
printing = cups
printcap name = cups
[printers]
comment = All Printers
path = /var/spool/samba
browseable = no
guest ok = yes
writable = no
printable = yes
printer admin = root, @ntadmins, @smbprintadm
[homes]
comment = User home directories
valid users = @smbusers
browsable = no
writable = yes
guest ok = no
[apps]
comment = Shared /usr/local/apps directory
path = /usr/local/apps
browsable = yes
writable = no
guest ok = yes
The [global] section contains settings for the Samba server. In this example, the server is assumed
to be a member of an Active Directory (AD) domain that is running in native mode. Samba relies on
tickets issued by the Kerberos server to authenticate clients who want to access local services.
For more information, see Section 20.3.2, “About Samba Configuration for Windows Workgroups and
Domains”.
The [printers] section specifies support for print services. The path parameter specifies the
location of a spooling directory that receives print jobs from Windows clients before submitting them to
the local print spooler. Samba advertises all locally configured printers on the server.
The [homes] section provide a personal share for each user in the smbusers group. The settings for
browsable and writable prevent other users from browsing home directories, while allowing full
access to valid users.
The [apps] section specifies a share named apps, which grants Windows users browsing and readonly permission to the /usr/local/apps directory.
3. Allow incoming TCP connections to ports 139 and 445, and incoming UDP datagrams on ports 137 and
138 from the local network:
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m state --state NEW -m tcp –-dport 139 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m state --state NEW -m tcp –-dport 445 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m udp –-dport 137 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m udp –-dport 138 -j ACCEPT
# service iptables save
tcp \
tcp \
udp \
udp \
where subnet_addr/prefix_length specifies the network address, for example
192.168.2.0/24.
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About Samba Configuration for Windows Workgroups and Domains
Add similar rules for other networks from which Samba clients can connect.
The nmdb daemon services NetBIOS Name Service requests on UDP port 137 and NetBIOS Datagram
Service requests on UDP port 138.
The smbd daemon services NetBIOS Session Service requests on TCP port 139 and Microsoft
Directory Service requests on TCP port 445.
4. Start the smb service, and configure the service to start following a system reboot:
# service smb start
# chkconfig smb on
If you change the /etc/samba/smb.conf file and any files that it references, the smb service will
reload its configuration automatically after a delay of up to one minute. You can force smb to reload its
configuration by sending a SIGHUP signal to the service daemon:
# killall -SIGHUP smbd
Making smb reload its configuration has no effect on established connections. You must restart the smb
service or the existing users of the service must disconnect and then reconnect.
To restart the smb service, use the following command:
# service smb restart
For more information, see the smb.conf(5) and smbd(8) manual pages and http://www.samba.org/
samba/docs/.
20.3.2 About Samba Configuration for Windows Workgroups and Domains
Windows systems on an enterprise network usually belong either to a workgroup or to a domain.
Workgroups are usually only configured on networks that connect a small number of computers. A
workgroup environment is a peer-to-peer network where systems do not rely on each other for services
and there is no centralized management. User accounts, access control, and system resources are
configured independently on each system. Such systems can share resources only if configured to do so.
A Samba server can act as a standalone server within a workgroup.
More typically, corporate networks configure domains to allow large numbers of networked systems to be
administered centrally. A domain is a group of trusted computers that share security and access control.
Systems known as domain controllers provides centralized management and security. Windows domains
are usually configured to use Active Directory (AD), which uses the Lightweight Directory Access Protocol
(LDAP) to implement versions of Kerberos and DNS providing authentication, access control to domain
resources, and name service. Some Windows domains use Windows NT4 security, which does not use
Kerberos to perform authentication.
A Samba server can be a member of an AD or NT4 security domain, but it cannot operate as a domain
controller. As domain member Samba server must authenticate itself with a domain controller and so is
controlled by the security rules of the domain. The domain controller authenticates clients, and the Samba
server controls access to printers and network shares.
20.3.2.1 Configuring Samba as a Standalone Server
A standalone Samba server can be a member of a workgroup. The following [global] section from /
etc/samba/smb.conf shows an example of how to configure a standalone server using share-level
security:
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About Samba Configuration for Windows Workgroups and Domains
[global]
security = share
workgroup = workgroup_name
netbios name = netbios_name
The client provides only a password and not a user name to the server. Typically, each share is associated
with a valid users parameter and the server validates the password against the hashed passwords
stored in /etc/passwd, /etc/shadow, NIS, or LDAP for the listed users. Using share-level security is
discouraged in favor of user-level security, for example:
[global]
security = user
workgroup = workgroup_name
netbios name = netbios_name
In the user security model, a client must supply a valid user name and password. This model supports
encrypted passwords. If the server successfully validates the client's user name and password, the client
can mount multiple shares without being required to specify a password. Use the smbpasswd command to
create an entry for a user in the Samba password file, for example:
# smbpasswd –a guest
New SMB password: password
Retype new SMB password: password
Added user guest.
The user must already exist as a user on the system. If a user is permitted to log into the server, he or she
can use the smbpasswd command to change his or her password.
If a Windows user has a different user name from his or her user name on the Samba server, create a
mapping between the names in the /etc/samba/smbusers file, for example:
root = admin administrator root
nobody = guest nobody pcguest smbguest
eddie = ejones
fiona = fchau
The first entry on each line is the user name on the Samba server. The entries after the equals sign (=) are
the equivalent Windows user names.
Note
Only the user security model uses Samba passwords.
The server security model, where the Samba server relies on another server to authenticate user names
and passwords, is deprecated as it has numerous security and interoperability issues.
20.3.2.2 Configuring Samba as a Member of an ADS Domain
In the Activity Directory Server (ADS) security model, Samba acts as a domain member server in an
ADS realm, and clients use Kerberos tickets for Active Directory authentication. You must configure
Kerberos and join the server to the domain, which creates a machine account for your server on the
domain controller.
To add a Samba server to an Active Directory domain:
1. Edit /etc/samba/smb.conf and configure the [global] section to use ADS:
[global]
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About Samba Configuration for Windows Workgroups and Domains
security = ADS
realm = KERBEROS.REALM
It might also be necessary to specify the password server explicitly if different servers support AD
services and Kerberos authentication:
password server = kerberos_server.your_domain
2. Install the krb5-server package:
# yum install krb5-server
3. Create a Kerberos ticket for the Administrator account in the Kerberos domain, for example:
# kinit [email protected]
This command creates the Kerberos ticket that is required to join the server to the AD domain.
4. Join the server to the AD domain:
# net ads join -S winads.mydom.com -U Administrator%password
In this example, the AD server is winads.mydom.com and password is the password for the
Administrator account.
The command creates a machine account in Active Directory for the Samba server and allows it to join
the domain.
5. Restart the smb service:
# service smb restart
20.3.2.3 Configuring Samba as a Member of a Windows NT4 Security Domain
Note
If the Samba server acts as a Primary or Backup Domain Controller, do not use
the domain security model. Configure the system as a standalone server that uses
the user security model instead. See Section 20.3.2.1, “Configuring Samba as a
Standalone Server”.
The domain security model is used with domains that implement Windows NT4 security. The Samba
server must have a machine account in the domain (a domain security trust account). Samba authenticates
user names and passwords with either a primary or a secondary domain controller.
To add a Samba server to an NT4 domain:
1. On the primary domain controller, use the Server Manager to add a machine account for the Samba
server.
2. Edit /etc/samba/smb.conf and configure the [global] section to use ADS:
[global]
security = domain
workgroup = DOMAIN
netbios name = SERVERNAME
3. Join the server to the domain:
# net rpc join -S winpdc.mydom.com -U Administrator%password
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Accessing Samba Shares from a Windows Client
In this example, the primary domain controller is winpdc.mydom.com and password is the password
for the Administrator account.
4. Restart the smb service:
# service smb restart
5. Create an account for each user who is allowed access to shares or printers:
# useradd -s /sbin/nologin username
# passwd username
In this example, the account's login shell is set to /sbin/nologin to prevent direct logins.
20.3.3 Accessing Samba Shares from a Windows Client
To access a share on a Samba server from Windows, open Computer or Windows Explorer, and enter the
host name of the Samba server and the share name using the following format:
\\server_name\share_name
If you enter \\server_name, Windows displays the directories and printers that the server is sharing. You
can also use the same syntax to map a network drive to a share name.
20.3.4 Accessing Samba Shares from an Oracle Linux Client
Note
To be able to use the commands described in this section, use yum to install the
samba-client and cifs-utils packages.
You can use the findsmb command to query a subnet for Samba servers. The command displays the IP
address, NetBIOS name, workgroup, operating system and version for each server that it finds.
Alternatively, you can use the smbtree command, which is a text-based SMB network browser that
displays the hierarchy of known domains, servers in those domains, and shares on those servers.
The GNOME and KDE desktops provide browser-based file managers that you can use to view Windows
shares on the network. Enter smb: in the location bar of a file manager to browse network shares.
To connect to a Windows share from the command line, use the smbclient command:
$ smbclient //server_name/share_name [-U username]
After logging in, enter help at the smb:\> prompt to display a list of available commands.
To mount a Samba share, use a command such as the following:
# mount -t cifs //server_name/share_name mountpoint -o credentials=credfile
where the credentials file contains settings for username, password, and domain, for example:
username=eddie
password=clydenw
domain=MYDOMWKG
The argument to domain can be the name of a domain or a workgroup.
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Accessing Samba Shares from an Oracle Linux Client
Caution
As the credentials file contains a plain-text password, use chmod to make it
readable only by you, for example:
# chmod 400 credfile
If the Samba server is a domain member server in an AD domain and your current login session was
authenticated by the Kerberos server in the domain, you can use your existing session credentials by
specifying the sec=krb5 option instead of a credentials file:
# mount -t cifs //server_name/share_name mountpoint -o sec=krb5
For more information, see the findsmb(1), mount.cifs(8), smbclient(1), and smbtree(1)
manual pages.
240
Chapter 21 Oracle Cluster File System Version 2
Table of Contents
21.1 About OCFS2 .........................................................................................................................
21.2 Installing and Configuring OCFS2 ............................................................................................
21.2.1 Preparing a Cluster for OCFS2 .....................................................................................
21.2.2 Configuring the Firewall ................................................................................................
21.2.3 Configuring the Cluster Software ...................................................................................
21.2.4 Creating the Configuration File for the Cluster Stack ......................................................
21.2.5 Configuring the Cluster Stack .......................................................................................
21.2.6 Configuring the Kernel for Cluster Operation ..................................................................
21.2.7 Starting and Stopping the Cluster Stack ........................................................................
21.2.8 Creating OCFS2 volumes .............................................................................................
21.2.9 Mounting OCFS2 Volumes ...........................................................................................
21.2.10 Querying and Changing Volume Parameters ...............................................................
21.3 Troubleshooting OCFS2 ..........................................................................................................
21.3.1 Recommended Tools for Debugging .............................................................................
21.3.2 Mounting the debugfs File System ................................................................................
21.3.3 Configuring OCFS2 Tracing ..........................................................................................
21.3.4 Debugging File System Locks .......................................................................................
21.3.5 Configuring the Behavior of Fenced Nodes ....................................................................
21.4 Use Cases for OCFS2 ............................................................................................................
21.4.1 Load Balancing ............................................................................................................
21.4.2 Oracle Real Application Cluster (RAC) ..........................................................................
21.4.3 Oracle Databases .........................................................................................................
21.5 For More Information About OCFS2 .........................................................................................
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243
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244
244
247
248
249
249
251
251
251
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252
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256
This chapter describes how to configure and use the Oracle Cluster File System Version 2 (OCFS2) file
system.
21.1 About OCFS2
Oracle Cluster File System version 2 (OCFS2) is a general-purpose, high-performance, high-availability,
shared-disk file system intended for use in clusters. It is also possible to mount an OCFS2 volume on a
standalone, non-clustered system.
Although it might seem that there is no benefit in mounting ocfs2 locally as compared to alternative file
systems such as ext4 or btrfs, you can use the reflink command with OCFS2 to create copy-onwrite clones of individual files in a similar way to using the cp --reflink command with the btrfs file
system. Typically, such clones allow you to save disk space when storing multiple copies of very similar
files, such as VM images or Linux Containers. In addition, mounting a local OCFS2 file system allows you
to subsequently migrate it to a cluster file system without requiring any conversion.
Almost all applications can use OCFS2 as it provides local file-system semantics. Applications that are
cluster-aware can use cache-coherent parallel I/O from multiple cluster nodes to balance activity across
the cluster, or they can use of the available file-system functionality to fail over and run on another node in
the event that a node fails. The following examples typify some use cases for OCFS2:
• Oracle VM to host shared access to virtual machine images.
• Oracle VM and VirtualBox to allow Linux guest machines to share a file system.
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Installing and Configuring OCFS2
• Oracle Real Application Cluster (RAC) in database clusters.
• Oracle E-Business Suite in middleware clusters.
OCFS2 has a large number of features that make it suitable for deployment in an enterprise-level
computing environment:
• Support for ordered and write-back data journaling that provides file system consistency in the event of
power failure or system crash.
• Block sizes ranging from 512 bytes to 4 KB, and file-system cluster sizes ranging from 4 KB to 1 MB
(both in increments in power of 2). The maximum supported volume size is 16 TB, which corresponds to
the maximum possible for a cluster size of 4 KB. A volume size as large as 4 PB is theoretically possible
for a cluster size of 1 MB, although this limit has not been tested.
• Extent-based allocations for efficient storage of very large files.
• Optimized allocation support for sparse files, inline-data, unwritten extents, hole punching, reflinks, and
allocation reservation for high performance and efficient storage.
• Indexing of directories to allow efficient access to a directory even if it contains millions of objects.
• Metadata checksums for the detection of corrupted inodes and directories.
• Extended attributes to allow an unlimited number of name:value pairs to be attached to file system
objects such as regular files, directories, and symbolic links.
• Advanced security support for POSIX ACLs and SELinux in addition to the traditional file-access
permission model.
• Support for user and group quotas.
• Support for heterogeneous clusters of nodes with a mixture of 32-bit and 64-bit, little-endian (x86,
x86_64, ia64) and big-endian (ppc64) architectures.
• An easy-to-configure, in-kernel cluster-stack (O2CB) with a distributed lock manager (DLM), which
manages concurrent access from the cluster nodes.
• Support for buffered, direct, asynchronous, splice and memory-mapped I/O.
• A tool set that uses similar parameters to the ext3 file system.
21.2 Installing and Configuring OCFS2
The procedures in the following sections describe how to set up a cluster to use OCFS2.
• Section 21.2.1, “Preparing a Cluster for OCFS2”
• Section 21.2.2, “Configuring the Firewall”
• Section 21.2.3, “Configuring the Cluster Software”
• Section 21.2.4, “Creating the Configuration File for the Cluster Stack”
• Section 21.2.5, “Configuring the Cluster Stack”
• Section 21.2.6, “Configuring the Kernel for Cluster Operation”
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Preparing a Cluster for OCFS2
• Section 21.2.7, “Starting and Stopping the Cluster Stack”
• Section 21.2.9, “Mounting OCFS2 Volumes”
21.2.1 Preparing a Cluster for OCFS2
For best performance, each node in the cluster should have at least two network interfaces. One interface
is connected to a public network to allow general access to the systems. The other interface is used for
private communication between the nodes; the cluster heartbeat that determines how the cluster nodes
coordinate their access to shared resources and how they monitor each other's state. These interface must
be connected via a network switch. Ensure that all network interfaces are configured and working before
continuing to configure the cluster.
You have a choice of two cluster heartbeat configurations:
• Local heartbeat thread for each shared device. In this mode, a node starts a heartbeat thread when
it mounts an OCFS2 volume and stops the thread when it unmounts the volume. This is the default
heartbeat mode. There is a large CPU overhead on nodes that mount a large number of OCFS2
volumes as each mount requires a separate heartbeat thread. A large number of mounts also increases
the risk of a node fencing itself out of the cluster due to a heartbeat I/O timeout on a single mount.
• Global heartbeat on specific shared devices. You can configure any OCFS2 volume as a global
heartbeat device provided that it occupies a whole disk device and not a partition. In this mode, the
heartbeat to the device starts when the cluster comes online and stops when the cluster goes offline.
This mode is recommended for clusters that mount a large number of OCFS2 volumes. A node fences
itself out of the cluster if a heartbeat I/O timeout occurs on more than half of the global heartbeat
devices. To provide redundancy against failure of one of the devices, you should therefore configure at
least three global heartbeat devices.
Figure 21.1 shows a shows a cluster of four nodes connected via a network switch to a LAN and a network
storage server. The nodes and the storage server are also connected via a switch to a private network that
they use for the local cluster heartbeat.
Figure 21.1 Cluster Configuration Using a Private Network
It is possible to configure and use OCFS2 without using a private network but such a configuration
increases the probability of a node fencing itself out of the cluster due to an I/O heartbeat timeout.
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Configuring the Firewall
21.2.2 Configuring the Firewall
Configure or disable the firewall on each node to allow access on the interface that the cluster will use for
private cluster communication. By default, the cluster uses both TCP and UDP over port 7777.
To allow incoming TCP connections and UDP datagrams on port 7777 from the private network, use the
following commands:
# iptables -I INPUT -s subnet_addr/prefix_length -p tcp \
-m state --state NEW -m tcp -–dport 7777 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p udp \
-m udp -–dport 7777 -j ACCEPT
# service iptables save
where subnet_addr/prefix_length specifies the network address of the private network, for example
10.0.1.0/24.
21.2.3 Configuring the Cluster Software
Ideally, each node should be running the same version of the OCFS2 software and a compatible version
of the Oracle Linux Unbreakable Enterprise Kernel (UEK). It is possible for a cluster to run with mixed
versions of the OCFS2 and UEK software, for example, while you are performing a rolling update of a
cluster. The cluster node that is running the lowest version of the software determines the set of usable
features.
Use yum to install or upgrade the following packages to the same version on each node:
• kernel-uek
• ocfs2-tools
Note
If you want to use the global heartbeat feature, you must install ocfs2tools-1.8.0-11 or later.
21.2.4 Creating the Configuration File for the Cluster Stack
You can create the configuration file by using the o2cb command or a text editor.
To configure the cluster stack by using the o2cb command:
1. Use the following command to create a cluster definition.
# o2cb add-cluster cluster_name
For example, to define a cluster named mycluster with four nodes:
# o2cb add-cluster mycluster
The command creates the configuration file /etc/ocfs2/cluster.conf if it does not already exist.
2. For each node, use the following command to define the node.
# o2cb add-node cluster_name node_name --ip ip_address
The name of the node must be same as the value of system's HOSTNAME that is configured in /etc/
sysconfig/network. The IP address is the one that the node will use for private communication in
the cluster.
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Creating the Configuration File for the Cluster Stack
For example, to define a node named node0 with the IP address 10.1.0.100 in the cluster mycluster:
# o2cb add-node mycluster node0 --ip 10.1.0.100
3. If you want the cluster to use global heartbeat devices, use the following commands.
# o2cb add-heartbeat cluster_name device1
.
.
.
# o2cb heartbeat-mode cluster_name global
Note
You must configure global heartbeat to use whole disk devices. You cannot
configure a global heartbeat device on a disk partition.
For example, to use /dev/sdd, /dev/sdg, and /dev/sdj as global heartbeat devices:
#
#
#
#
o2cb
o2cb
o2cb
o2cb
add-heartbeat mycluster /dev/sdd
add-heartbeat mycluster /dev/sdg
add-heartbeat mycluster /dev/sdj
heartbeat-mode mycluster global
4. Copy the cluster configuration file /etc/ocfs2/cluster.conf to each node in the cluster.
Note
Any changes that you make to the cluster configuration file do not take effect
until you restart the cluster stack.
The following sample configuration file /etc/ocfs2/cluster.conf defines a 4-node cluster named
mycluster with a local heartbeat.
node:
name = node0
cluster = mycluster
number = 0
ip_address = 10.1.0.100
ip_port = 7777
node:
name = node1
cluster = mycluster
number = 1
ip_address = 10.1.0.101
ip_port = 7777
node:
name = node2
cluster = mycluster
number = 2
ip_address = 10.1.0.102
ip_port = 7777
node:
name = node3
cluster = mycluster
number = 3
ip_address = 10.1.0.103
ip_port = 7777
cluster:
245
Creating the Configuration File for the Cluster Stack
name = mycluster
heartbeat_mode = local
node_count = 4
If you configure your cluster to use a global heartbeat, the file also include entries for the global heartbeat
devices.
node:
name = node0
cluster = mycluster
number = 0
ip_address = 10.1.0.100
ip_port = 7777
node:
name = node1
cluster = mycluster
number = 1
ip_address = 10.1.0.101
ip_port = 7777
node:
name = node2
cluster = mycluster
number = 2
ip_address = 10.1.0.102
ip_port = 7777
node:
name = node3
cluster = mycluster
number = 3
ip_address = 10.1.0.103
ip_port = 7777
cluster:
name = mycluster
heartbeat_mode = global
node_count = 4
heartbeat:
cluster = mycluster
region = 7DA5015346C245E6A41AA85E2E7EA3CF
heartbeat:
cluster = mycluster
region = 4F9FBB0D9B6341729F21A8891B9A05BD
heartbeat:
cluster = mycluster
region = B423C7EEE9FC426790FC411972C91CC3
The cluster heartbeat mode is now shown as global, and the heartbeat regions are represented by the
UUIDs of their block devices.
If you edit the configuration file manually, ensure that you use the following layout:
• The cluster:, heartbeat:, and node: headings must start in the first column.
• Each parameter entry must be indented by one tab space.
• A blank line must separate each section that defines the cluster, a heartbeat device, or a node.
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Configuring the Cluster Stack
21.2.5 Configuring the Cluster Stack
To configure the cluster stack:
1. Run the following command on each node of the cluster:
# service o2cb configure
The following table describes the values for which you are prompted.
Prompt
Description
Load O2CB driver on boot (y/n)
Whether the cluster stack driver should be loaded at boot
time. The default response is n.
Cluster stack backing O2CB
The name of the cluster stack service. The default and
usual response is o2cb.
Cluster to start at boot (Enter Enter the name of your cluster that you defined in the
"none" to clear)
cluster configuration file, /etc/ocfs2/cluster.conf.
Specify heartbeat dead
threshold (>=7)
The number of 2-second heartbeats that must elapse
without response before a node is considered dead. To
calculate the value to enter, divide the required threshold
time period by 2 and add 1. For example, to set the
threshold time period to 120 seconds, enter a value of 61.
The default value is 31, which corresponds to a threshold
time period of 60 seconds.
Note
If your system uses multipathed
storage, the recommended value is
61 or greater.
Specify network idle timeout in The time in milliseconds that must elapse before a
ms (>=5000)
network connection is considered dead. The default value
is 30,000 milliseconds.
Note
For bonded network interfaces,
the recommended value is 30,000
milliseconds or greater.
Specify network keepalive delay The maximum delay in milliseconds between sending
in ms (>=1000)
keepalive packets to another node. The default and
recommended value is 2,000 milliseconds.
Specify network reconnect delay The minimum delay in milliseconds between reconnection
in ms (>=2000)
attempts if a network connection goes down. The default
and recommended value is 2,000 milliseconds.
To verify the settings for the cluster stack, enter the service o2cb status command:
# service o2cb status
Driver for "configfs": Loaded
Filesystem "configfs": Mounted
Stack glue driver: Loaded
Stack plugin "o2cb": Loaded
Driver for "ocfs2_dlmfs": Loaded
247
Configuring the Kernel for Cluster Operation
Filesystem "ocfs2_dlmfs": Mounted
Checking O2CB cluster "mycluster": Online
Heartbeat dead threshold: 61
Network idle timeout: 30000
Network keepalive delay: 2000
Network reconnect delay: 2000
Heartbeat mode: Local
Checking O2CB heartbeat: Active
In this example, the cluster is online and is using local heartbeat mode. If no volumes have been
configured, the O2CB heartbeat is shown as Not active rather than Active.
The next example shows the command output for an online cluster that is using three global heartbeat
devices:
# service o2cb status
Driver for "configfs": Loaded
Filesystem "configfs": Mounted
Stack glue driver: Loaded
Stack plugin "o2cb": Loaded
Driver for "ocfs2_dlmfs": Loaded
Filesystem "ocfs2_dlmfs": Mounted
Checking O2CB cluster "mycluster":
Heartbeat dead threshold: 61
Network idle timeout: 30000
Network keepalive delay: 2000
Network reconnect delay: 2000
Heartbeat mode: Global
Checking O2CB heartbeat: Active
7DA5015346C245E6A41AA85E2E7EA3CF
4F9FBB0D9B6341729F21A8891B9A05BD
B423C7EEE9FC426790FC411972C91CC3
Online
/dev/sdd
/dev/sdg
/dev/sdj
2. Configure the o2cb and ocfs2 services so that they start at boot time after networking is enabled:
# chkconfig o2cb on
# chkconfig ocfs2 on
These settings allow the node to mount OCFS2 volumes automatically when the system starts.
21.2.6 Configuring the Kernel for Cluster Operation
For the correct operation of the cluster, you must configure the kernel settings shown in the following table:
Kernel Setting
Description
panic
Specifies the number of seconds after a panic before a system will automatically reset
itself.
If the value is 0, the system hangs, which allows you to collect detailed information
about the panic for troubleshooting. This is the default value.
To enable automatic reset, set a non-zero value. If you require a memory image
(vmcore), allow enough time for Kdump to create this image. The suggested value is
30 seconds, although large systems will require a longer time.
panic_on_oops Specifies that a system must panic if a kernel oops occurs. If a kernel thread required
for cluster operation crashes, the system must reset itself. Otherwise, another node
might not be able to tell whether a node is slow to respond or unable to respond,
causing cluster operations to hang.
On each node, enter the following commands to set the recommended values for panic and
panic_on_oops:
248
Starting and Stopping the Cluster Stack
# sysctl kernel.panic = 30
# sysctl kernel.panic_on_oops = 1
To make the change persist across reboots, add the following entries to the /etc/sysctl.conf file:
# Define panic and panic_on_oops for cluster operation
kernel.panic = 30
kernel.panic_on_oops = 1
21.2.7 Starting and Stopping the Cluster Stack
The following table shows the commands that you can use to perform various operations on the cluster
stack.
Command
Description
service o2cb status
Check the status of the cluster stack.
service o2cb online
Start the cluster stack.
service o2cb offline
Stop the cluster stack.
service o2cb unload
Unload the cluster stack.
21.2.8 Creating OCFS2 volumes
You can use the mkfs.ocfs2 command to create an OCFS2 volume on a device. If you want to label the
volume and mount it by specifying the label, the device must correspond to a partition. You cannot mount
an unpartitioned disk device by specifying a label. The following table shows the most useful options that
you can use when creating an OCFS2 volume.
Command Option
Description
-b block-size
Specifies the unit size for I/O transactions to and from the file system,
and the size of inode and extent blocks. The supported block sizes
are 512 bytes, 1 KB, 2 KB, and 4 KB. The default and recommended
block size is 4K (4 KB).
--block-size block-size
-C cluster-size
--cluster-size clustersize
--fs-featurelevel=feature-level
--fs_features=feature
Specifies the unit size for space used to allocate file data. The
supported cluster sizes are 4KB, 8KB, 16 KB, 32 KB, 64 KB, 128 KB,
256 KB, 512 KB, and 1 MB. The default cluster size is 4K (4 KB). If
you intend the volume to store database files, do not specify a cluster
size that is smaller than the block size of the database.
Allows you select a set of file-system features:
default
Enables support for the sparse
files, unwritten extents, and inline
data features.
max-compat
Enables only those features that
are understood by older versions of
OCFS2.
max-features
Enables all features that OCFS2
currently supports.
Allows you to enable or disable individual features such as support
for sparse files, unwritten extents, and backup superblocks. For more
information, see the mkfs.ocfs2(8) manual page.
249
Creating OCFS2 volumes
Command Option
Description
-J size=journal-size
Specifies the size of the write-ahead journal. If not specified, the size
is determined from the file system usage type that you specify to the T option, and, otherwise, from the volume size. The default size of the
journal is 64M (64 MB) for datafiles, 256M (256 MB) for mail, and
128M (128 MB) for vmstore.
--journal-options
size=journal-size
-L volume-label
Specifies a descriptive name for the volume that allows you to identify
it easily on different cluster nodes.
--label volume-label
-N number
--node-slots number
-T file-system-usage-type
Determines the maximum number of nodes that can concurrently
access a volume, which is limited by the number of node slots for
system files such as the file-system journal. For best performance,
set the number of node slots to at least twice the number of nodes. If
you subsequently increase the number of node slots, performance can
suffer because the journal will no longer be contiguously laid out on
the outer edge of the disk platter.
Specifies the type of usage for the file system:
datafiles
Database files are typically few
in number, fully allocated, and
relatively large. Such files require
few metadata changes, and do not
benefit from having a large journal.
mail
Mail server files are typically many
in number, and relatively small.
Such files require many metadata
changes, and benefit from having a
large journal.
vmstore
Virtual machine image files are
typically few in number, sparsely
allocated, and relatively large. Such
files require a moderate number of
metadata changes and a medium
sized journal.
For example, create an OCFS2 volume on /dev/sdc1 labeled as myvol using all the default settings for
generic usage (4 KB block and cluster size, eight node slots, a 256 MB journal, and support for default filesystem features).
# mkfs.ocfs2 -L "myvol" /dev/sdc1
Create an OCFS2 volume on /dev/sdd2 labeled as dbvol for use with database files. In this case, the
cluster size is set to 128 KB and the journal size to 32 MB.
# mkfs.ocfs2 -L "dbvol" -T datafiles /dev/sdd2
Create an OCFS2 volume on /dev/sde1 with a 16 KB cluster size, a 128 MB journal, 16 node slots, and
support enabled for all features except refcount trees.
# mkfs.ocfs2 -C 16K -J size=128M -N 16 --fs-feature-level=max-features \
--fs-features=norefcount /dev/sde1
250
Mounting OCFS2 Volumes
Note
Do not create an OCFS2 volume on an LVM logical volume. LVM is not clusteraware.
You cannot change the block and cluster size of an OCFS2 volume after it
has been created. You can use the tunefs.ocfs2 command to modify other
settings for the file system with certain restrictions. For more information, see the
tunefs.ocfs2(8) manual page.
21.2.9 Mounting OCFS2 Volumes
As shown in the following example, specify the _netdev option in /etc/fstab if you want the system to
mount an OCFS2 volume at boot time after networking is started, and to unmount the file system before
networking is stopped.
myocfs2vol
/dbvol1
ocfs2
_netdev,defaults
0 0
Note
The file system will not mount unless you have enabled the o2cb and ocfs2
services to start after networking is started. See Section 21.2.5, “Configuring the
Cluster Stack”.
21.2.10 Querying and Changing Volume Parameters
You can use the tunefs.ocfs2 command to query or change volume parameters. For example, to find
out the label, UUID and the number of node slots for a volume:
# tunefs.ocfs2 -Q "Label = %V\nUUID = %U\nNumSlots =%N\n" /dev/sdb
Label = myvol
UUID = CBB8D5E0C169497C8B52A0FD555C7A3E
NumSlots = 4
Generate a new UUID for a volume:
# tunefs.ocfs2 -U /dev/sda
# tunefs.ocfs2 -Q "Label = %V\nUUID = %U\nNumSlots =%N\n" /dev/sdb
Label = myvol
UUID = 48E56A2BBAB34A9EB1BE832B3C36AB5C
NumSlots = 4
21.3 Troubleshooting OCFS2
The following sections describes some techniques that you can use for investigating any problems that you
encounter with OCFS2.
21.3.1 Recommended Tools for Debugging
To you want to capture an oops trace, it is recommended that you set up netconsole on the nodes.
If you want to capture the DLM's network traffic between the nodes, you can use tcpdump. For example, to
capture TCP traffic on port 7777 for the private network interface eth1, you could use a command such as
the following:
# tcpdump -i eth1 -C 10 -W 15 -s 10000 -Sw /tmp/`hostname -s`_tcpdump.log \
-ttt 'port 7777' &
251
Mounting the debugfs File System
You can use the debugfs.ocfs2 command, which is similar in behavior to the debugfs command for
the ext3 file system, and allows you to trace events in the OCFS2 driver, determine lock statuses, walk
directory structures, examine inodes, and so on.
For more information, see the debugfs.ocfs2(8) manual page.
The o2image command saves an OCFS2 file system's metadata (including information about inodes,
file names, and directory names) to an image file on another file system. As the image file contains only
metadata, it is much smaller than the original file system. You can use debugfs.ocfs2 to open the image
file, and analyze the file system layout to determine the cause of a file system corruption or performance
problem.
For example, the following command creates the image /tmp/sda2.img from the OCFS2 file system on
the device /dev/sda2:
# o2image /dev/sda2 /tmp/sda2.img
For more information, see the o2image(8) manual page.
21.3.2 Mounting the debugfs File System
OCFS2 uses the debugfs file system to allow access from user space to information about its in-kernel
state. You must mount the debugfs file system to be able to use the debugfs.ocfs2 command.
To mount the debugfs file system, add the following line to /etc/fstab:
debugfs
/sys/kernel/debug
debugfs
defaults
0 0
and run the mount -a command.
21.3.3 Configuring OCFS2 Tracing
The following table shows some of the commands that are useful for tracing problems in OCFS2.
252
Debugging File System Locks
Command
Description
debugfs.ocfs2 -l
List all trace bits and their statuses.
debugfs.ocfs2 -l SUPER allow
Enable tracing for the superblock.
debugfs.ocfs2 -l SUPER off
Disable tracing for the superblock.
debugfs.ocfs2 -l SUPER deny
Disallow tracing for the superblock, even if implicitly
enabled by another tracing mode setting.
debugfs.ocfs2 -l HEARTBEAT \
Enable heartbeat tracing.
ENTRY EXIT allow
Disable heartbeat tracing. ENTRY and EXIT are set
to deny as they exist in all trace paths.
debugfs.ocfs2 -l HEARTBEAT off \
ENTRY EXIT deny
Enable tracing for the file system.
debugfs.ocfs2 -l ENTRY EXIT \
NAMEI INODE allow
Disable tracing for the file system.
debugfs.ocfs2 -l ENTRY EXIT \
deny NAMEI INODE allow
Enable tracing for the DLM.
debugfs.ocfs2 -l ENTRY EXIT \
DLM DLM_THREAD allow
Disable tracing for the DLM.
debugfs.ocfs2 -l ENTRY EXIT \
deny DLM DLM_THREAD allow
One method for obtaining a trace its to enable the trace, sleep for a short while, and then disable the trace.
As shown in the following example, to avoid seeing unnecessary output, you should reset the trace bits to
their default settings after you have finished.
# debugfs.ocfs2 -l ENTRY EXIT NAMEI INODE allow && sleep 10 && \
debugfs.ocfs2 -l ENTRY EXIT deny NAMEI INODE off
To limit the amount of information displayed, enable only the trace bits that you believe are relevant to
understanding the problem.
If you believe a specific file system command, such as mv, is causing an error, the following example
shows the commands that you can use to help you trace the error.
#
#
#
#
debugfs.ocfs2 -l ENTRY EXIT NAMEI INODE allow
mv source destination & CMD_PID=$(jobs -p %-)
echo $CMD_PID
debugfs.ocfs2 -l ENTRY EXIT deny NAMEI INODE off
As the trace is enabled for all mounted OCFS2 volumes, knowing the correct process ID can help you to
interpret the trace.
For more information, see the debugfs.ocfs2(8) manual page.
21.3.4 Debugging File System Locks
If an OCFS2 volume hangs, you can use the following steps to help you determine which locks are busy
and the processes that are likely to be holding the locks.
1. Mount the debug file system.
253
Debugging File System Locks
# mount -t debugfs debugfs /sys/kernel/debug
2. Dump the lock statuses for the file system device (/dev/sdx1 in this example).
# echo "fs_locks" | debugfs.ocfs2 /dev/sdx1 >/tmp/fslocks 62
Lockres: M00000000000006672078b84822 Mode: Protected Read
Flags: Initialized Attached
RO Holders: 0 EX Holders: 0
Pending Action: None Pending Unlock Action: None
Requested Mode: Protected Read Blocking Mode: Invalid
The Lockres field is the lock name used by the DLM. The lock name is a combination of a lock-type
identifier, an inode number, and a generation number. The following table shows the possible lock
types.
Identifier
Lock Type
D
File data.
M
Metadata.
R
Rename.
S
Superblock.
W
Read-write.
3. Use the Lockres value to obtain the inode number and generation number for the lock.
# echo "stat <M00000000000006672078b84822>" | debugfs.ocfs2 -n /dev/sdx1
Inode: 419616
Mode: 0666
Generation: 2025343010 (0x78b84822)
...
4. Determine the file system object to which the inode number relates by using the following command.
# echo "locate <419616>" | debugfs.ocfs2 -n /dev/sdx1
419616 /linux-2.6.15/arch/i386/kernel/semaphore.c
5. Obtain the lock names that are associated with the file system object.
# echo "encode /linux-2.6.15/arch/i386/kernel/semaphore.c" | \
debugfs.ocfs2 -n /dev/sdx1
M00000000000006672078b84822 D00000000000006672078b84822 W00000000000006672078b84822
In this example, a metadata lock, a file data lock, and a read-write lock are associated with the file
system object.
6. Determine the DLM domain of the file system.
# echo "stats" | debugfs.ocfs2 -n /dev/sdX1 | grep UUID: | while read a b ; do echo $b ; done
82DA8137A49A47E4B187F74E09FBBB4B
7. Use the values of the DLM domain and the lock name with the following command, which enables
debugging for the DLM.
# echo R 82DA8137A49A47E4B187F74E09FBBB4B \
M00000000000006672078b84822 > /proc/fs/ocfs2_dlm/debug
8. Examine the debug messages.
# dmesg | tail
struct dlm_ctxt: 82DA8137A49A47E4B187F74E09FBBB4B, node=3, key=965960985
lockres: M00000000000006672078b84822, owner=1, state=0 last used: 0,
on purge list: no granted queue:
254
Configuring the Behavior of Fenced Nodes
type=3, conv=-1, node=3, cookie=11673330234144325711, ast=(empty=y,pend=n),
bast=(empty=y,pend=n)
converting queue:
blocked queue:
The DLM supports 3 lock modes: no lock (type=0), protected read (type=3), and exclusive (type=5).
In this example, the lock is mastered by node 1 (owner=1) and node 3 has been granted a protectedread lock on the file-system resource.
9. Run the following command, and look for processes that are in an uninterruptable sleep state as shown
by the D flag in the STAT column.
# ps -e -o pid,stat,comm,wchan=WIDE-WCHAN-COLUMN
At least one of the processes that are in the uninterruptable sleep state will be responsible for the hang
on the other node.
If a process is waiting for I/O to complete, the problem could be anywhere in the I/O subsystem from
the block device layer through the drivers to the disk array. If the hang concerns a user lock (flock()),
the problem could lie in the application. If possible, kill the holder of the lock. If the hang is due to lack of
memory or fragmented memory, you can free up memory by killing non-essential processes. The most
immediate solution is to reset the node that is holding the lock. The DLM recovery process can then clear
all the locks that the dead node owned, so letting the cluster continue to operate.
21.3.5 Configuring the Behavior of Fenced Nodes
If a node with a mounted OCFS2 volume believes that it is no longer in contact with the other cluster
nodes, it removes itself from the cluster in a process termed fencing. Fencing prevents other nodes from
hanging when they try to access resources held by the fenced node. By default, a fenced node restarts
instead of panicking so that it can quickly rejoin the cluster. Under some circumstances, you might want a
fenced node to panic instead of restarting. For example, you might want to use netconsole to view the
oops stack trace or to diagnose the cause of frequent reboots. To configure a node to panic when it next
fences, run the following command on the node after the cluster starts:
# echo panic > /sys/kernel/config/cluster/cluster_name/fence_method
where cluster_name is the name of the cluster. To set the value after each reboot of the system, add
this line to /etc/rc.local. To restore the default behavior, use the value reset instead of panic.
21.4 Use Cases for OCFS2
The following sections describe some typical use cases for OCFS2.
21.4.1 Load Balancing
You can use OCFS2 nodes to share resources between client systems. For example, the nodes could
export a shared file system by using Samba or NFS. To distribute service requests between the nodes, you
can use round-robin DNS, a network load balancer, or specify which node should be used on each client.
21.4.2 Oracle Real Application Cluster (RAC)
Oracle RAC uses its own cluster stack, Cluster Synchronization Services (CSS). You can use O2CB in
conjunction with CSS, but you should note that each stack is configured independently for timeouts, nodes,
and other cluster settings. You can use OCFS2 to host the voting disk files and the Oracle cluster registry
(OCR), but not the grid infrastructure user's home, which must exist on a local file system on each node.
255
Oracle Databases
As both CSS and O2CB use the lowest node number as a tie breaker in quorum calculations, you should
ensure that the node numbers are the same in both clusters. If necessary, edit the O2CB configuration file
/etc/ocfs2/cluster.conf to make the node numbering consistent, and update this file on all nodes.
The change takes effect when the cluster is restarted.
21.4.3 Oracle Databases
Specify the noatime option when mounting volumes that host Oracle datafiles, control files, redo logs,
voting disk, and OCR. The noatime option disables unnecessary updates to the access time on the
inodes.
Specify the nointr mount option to prevent signals interrupting I/O transactions that are in progress.
By default, the init.ora parameter filesystemio_options directs the database to perform direct I/O
to the Oracle datafiles, control files, and redo logs. You should also specify the datavolume mount option
for the volumes that contain the voting disk and OCR. Do not specify this option for volumes that host the
Oracle user's home directory or Oracle E-Business Suite.
To avoid database blocks becoming fragmented across a disk, ensure that the file system cluster size is at
least as big as the database block size, which is typically 8KB. If you specify the file system usage type as
datafiles to the mkfs.ocfs2 command, the file system cluster size is set to 128KB.
To allow multiple nodes to maximize throughput by concurrently streaming data to an Oracle datafile,
OCFS2 deviates from the POSIX standard by not updating the modification time (mtime) on the disk when
performing non-extending direct I/O writes. The value of mtime is updated in memory, but OCFS2 does
not write the value to disk unless an application extends or truncates the file, or performs a operation to
change the file metadata, such as using the touch command. This behavior leads to results in different
nodes reporting different time stamps for the same file. You can use the following command to view the ondisk timestamp of a file:
# debugfs.ocfs2 -R "stat /file_path" device | grep "mtime:"
21.5 For More Information About OCFS2
You can find more information about OCFS2 at https://oss.oracle.com/projects/ocfs2/documentation/.
256
Part IV Authentication and Security
This section contains the following chapters:
• Chapter 22, Authentication Configuration describes how to configure various authentication methods that Oracle
Linux can use, including NIS, LDAP, Kerberos, and Winbind, and how you can configure the System Security
Services Daemon feature to provide centralized identity and authentication management.
• Chapter 23, Local Account Configuration describes how to configure and manage local user and group accounts.
• Chapter 24, System Security Administration describes the subsystems that you can use to administer system
security, including SELinux, the Netfilter firewall, TCP Wrappers, chroot jails, auditing, system logging, and process
accounting.
• Chapter 25, OpenSSH Configuration describes how to configure OpenSSH to support secure communication
between networked systems.
Table of Contents
22 Authentication Configuration ....................................................................................................... 261
22.1 About Authentication ....................................................................................................... 261
22.2 About Local Oracle Linux Authentication .......................................................................... 262
22.2.1 Configuring Local Access ..................................................................................... 263
22.2.2 Configuring Fingerprint Reader Authentication ....................................................... 265
22.2.3 Configuring Smart Card Authentication .................................................................. 265
22.3 About IPA ....................................................................................................................... 266
22.3.1 Configuring IPA .................................................................................................... 266
22.4 About LDAP Authentication ............................................................................................. 266
22.4.1 About LDAP Data Interchange Format .................................................................. 267
22.4.2 Configuring an LDAP Server ................................................................................. 267
22.4.3 Replacing the Default Certificates ......................................................................... 270
22.4.4 Creating and Distributing Self-signed CA Certificates .............................................. 271
22.4.5 Initializing an Organization in LDAP ...................................................................... 274
22.4.6 Adding an Automount Map to LDAP ...................................................................... 275
22.4.7 Adding a Group to LDAP ...................................................................................... 275
22.4.8 Adding a User to LDAP ........................................................................................ 276
22.4.9 Adding Users to a Group in LDAP ........................................................................ 278
22.4.10 Enabling LDAP Authentication ............................................................................. 279
22.5 About NIS Authentication ................................................................................................ 283
22.5.1 About NIS Maps ................................................................................................... 284
22.5.2 Configuring an NIS Server .................................................................................... 284
22.5.3 Adding User Accounts to NIS ............................................................................... 288
22.5.4 Enabling NIS Authentication .................................................................................. 289
22.6 About Kerberos Authentication ......................................................................................... 291
22.6.1 Configuring a Kerberos Server .............................................................................. 294
22.6.2 Configuring a Kerberos Client ............................................................................... 296
22.6.3 Enabling Kerberos Authentication .......................................................................... 297
22.7 About Pluggable Authentication Modules .......................................................................... 300
22.7.1 Configuring Pluggable Authentication Modules ....................................................... 300
22.8 About the System Security Services Daemon ................................................................... 301
22.8.1 Configuring an SSSD Server ................................................................................ 302
22.9 About Winbind Authentication .......................................................................................... 304
22.9.1 Enabling Winbind Authentication ........................................................................... 304
23 Local Account Configuration ....................................................................................................... 307
23.1 About User and Group Configuration ............................................................................... 307
23.2 Changing Default Settings for User Accounts ................................................................... 308
23.3 Creating User Accounts ................................................................................................... 308
23.3.1 About umask and the setgid and Restricted Deletion Bits ....................................... 309
23.4 Locking an Account ......................................................................................................... 309
23.5 Modifying or Deleting User Accounts ............................................................................... 309
23.6 Creating Groups .............................................................................................................. 310
23.7 Modifying or Deleting Groups .......................................................................................... 310
23.8 Configuring Password Ageing .......................................................................................... 310
23.9 Granting sudo Access to Users ....................................................................................... 311
24 System Security Administration .................................................................................................. 313
24.1 About System Security .................................................................................................... 313
24.2 Configuring and Using SELinux ....................................................................................... 314
24.2.1 About SELinux Administration ............................................................................... 315
24.2.2 About SELinux Modes .......................................................................................... 317
24.2.3 Setting SELinux Modes ........................................................................................ 317
259
24.2.4 About SELinux Policies ......................................................................................... 317
24.2.5 About SELinux Context ......................................................................................... 319
24.2.6 About SELinux Users ........................................................................................... 321
24.2.7 Troubleshooting Access-Denial Messages ............................................................. 322
24.3 About Packet-filtering Firewalls ........................................................................................ 323
24.3.1 Controlling the Firewall Service ............................................................................. 325
24.3.2 Listing Firewall Rules ........................................................................................... 325
24.3.3 Inserting and Replacing Rules in a Chain .............................................................. 326
24.3.4 Deleting Rules in a Chain ..................................................................................... 327
24.3.5 Saving Rules ........................................................................................................ 327
24.4 About TCP Wrappers ...................................................................................................... 327
24.5 About chroot Jails ........................................................................................................... 329
24.5.1 Running DNS and FTP Services in a Chroot Jail ................................................... 329
24.5.2 Creating a Chroot Jail .......................................................................................... 329
24.5.3 Using a Chroot Jail .............................................................................................. 330
24.6 About Auditing ................................................................................................................ 330
24.7 About System Logging .................................................................................................... 331
24.7.1 Configuring Logwatch ........................................................................................... 334
24.8 About Process Accounting ............................................................................................... 335
24.9 Security Guidelines ......................................................................................................... 335
24.9.1 Minimizing the Software Footprint ......................................................................... 335
24.9.2 Configuring System Logging ................................................................................. 337
24.9.3 Disabling Core Dumps .......................................................................................... 337
24.9.4 Minimizing Active Services .................................................................................... 337
24.9.5 Locking Down Network Services ........................................................................... 340
24.9.6 Configuring a Packet-filtering Firewall .................................................................... 341
24.9.7 Configuring TCP Wrappers ................................................................................... 341
24.9.8 Configuring Kernel Parameters ............................................................................. 341
24.9.9 Restricting Access to SSH Connections ................................................................ 342
24.9.10 Configuring File System Mounts, File Permissions, and File Ownerships ................ 342
24.9.11 Checking User Accounts and Privileges ............................................................... 344
25 OpenSSH Configuration ............................................................................................................. 347
25.1 About OpenSSH ............................................................................................................. 347
25.2 OpenSSH Configuration Files .......................................................................................... 347
25.2.1 OpenSSH User Configuration Files ....................................................................... 348
25.3 Configuring an OpenSSH Server ..................................................................................... 349
25.4 Installing the OpenSSH Client Packages .......................................................................... 349
25.5 Using the OpenSSH Utilities ............................................................................................ 349
25.5.1 Using ssh to Connect to Another System .............................................................. 350
25.5.2 Using scp and sftp to Copy Files Between Systems ............................................... 351
25.5.3 Using ssh-keygen to Generate Pairs of Authentication Keys ................................... 352
25.5.4 Enabling Remote System Access Without Requiring a Password ............................ 352
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Chapter 22 Authentication Configuration
Table of Contents
22.1 About Authentication ...............................................................................................................
22.2 About Local Oracle Linux Authentication ..................................................................................
22.2.1 Configuring Local Access .............................................................................................
22.2.2 Configuring Fingerprint Reader Authentication ...............................................................
22.2.3 Configuring Smart Card Authentication ..........................................................................
22.3 About IPA ...............................................................................................................................
22.3.1 Configuring IPA ............................................................................................................
22.4 About LDAP Authentication .....................................................................................................
22.4.1 About LDAP Data Interchange Format ..........................................................................
22.4.2 Configuring an LDAP Server .........................................................................................
22.4.3 Replacing the Default Certificates .................................................................................
22.4.4 Creating and Distributing Self-signed CA Certificates .....................................................
22.4.5 Initializing an Organization in LDAP ..............................................................................
22.4.6 Adding an Automount Map to LDAP ..............................................................................
22.4.7 Adding a Group to LDAP ..............................................................................................
22.4.8 Adding a User to LDAP ................................................................................................
22.4.9 Adding Users to a Group in LDAP ................................................................................
22.4.10 Enabling LDAP Authentication .....................................................................................
22.5 About NIS Authentication ........................................................................................................
22.5.1 About NIS Maps ...........................................................................................................
22.5.2 Configuring an NIS Server ............................................................................................
22.5.3 Adding User Accounts to NIS .......................................................................................
22.5.4 Enabling NIS Authentication ..........................................................................................
22.6 About Kerberos Authentication .................................................................................................
22.6.1 Configuring a Kerberos Server ......................................................................................
22.6.2 Configuring a Kerberos Client .......................................................................................
22.6.3 Enabling Kerberos Authentication ..................................................................................
22.7 About Pluggable Authentication Modules ..................................................................................
22.7.1 Configuring Pluggable Authentication Modules ...............................................................
22.8 About the System Security Services Daemon ...........................................................................
22.8.1 Configuring an SSSD Server ........................................................................................
22.9 About Winbind Authentication ..................................................................................................
22.9.1 Enabling Winbind Authentication ...................................................................................
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This chapter describes how to configure various authentication methods that Oracle Linux can use,
including NIS, LDAP, Kerberos, and Winbind, and how you can configure the System Security Services
Daemon feature to provide centralized identity and authentication management.
22.1 About Authentication
Authentication is the verification of the identity of an entity, such as a user, to a system. A user logs in
by providing a user name and a password, and the operating system authenticates the user's identity
by comparing this information to data stored on the system. If the login credentials match and the user
account is active, the user is authenticated and can successfully access the system.
The information that verifies a user's identity can either be located on the local system in the /etc/
passwd and /etc/shadow files, or on remote systems using Identity Policy Audit (IPA), the Lightweight
Directory Access Protocol (LDAP), the Network Information Service (NIS), or Winbind. In addition, IPSv2,
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About Local Oracle Linux Authentication
LDAP, and NIS data files can use the Kerberos authentication protocol, which allows nodes communicating
over a non-secure network to prove their identity to one another in a secure manner.
You can use the Authentication Configuration GUI (system-config-authentication) to select the
authentication mechanism and to configure any associated authentication options. Alternatively, you can
use the authconfig command. Both the Authentication Configuration GUI and authconfig adjust
settings in the PAM configuration files that are located in the /etc/pam.d directory.
Figure 22.1 shows the Authentication Configuration GUI with Local accounts only selected.
Figure 22.1 Authentication Configuration of Local Accounts
22.2 About Local Oracle Linux Authentication
Unless you select a different authentication mechanism during installation or by using the Authentication
Configuration GUI or the authconfig command, Oracle Linux verifies a user's identity by using the
information that is stored in the /etc/passwd and /etc/shadow files.
The /etc/passwd file stores account information for each user such as his or her unique user ID (or UID,
which is an integer), user name, home directory, and login shell. A user logs in using his or her user name,
but the operating system uses the associated UID. When the user logs in, he or she is placed in his or her
home directory and his or her login shell runs.
The /etc/group file stores information about groups of users. A user also belongs to one or more
groups, and each group can contain one or more users. If you can grant access privileges to a group, all
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Configuring Local Access
members of the group receive the same access privileges. Each group account has a unique group ID
(GID, again an integer) and an associated group name.
By default, Oracle Linux implements the user private group (UPG) scheme where adding a user account
also creates a corresponding UPG with the same name as the user, and of which the user is the only
member.
Only the root user can add, modify, or delete user and group accounts. By default, both users and groups
use shadow passwords, which are cryptographically hashed and stored in /etc/shadow and /etc/
gshadow respectively. These shadow password files are readable only by the root user. root can set a
group password that a user must enter to become a member of the group by using the newgrp command.
If a group does not have a password, a user can only join the group by root adding him or her as a
member.
The /etc/login.defs file defines parameters for password aging and related security policies.
For more information about the content of these files, see the group(5), gshadow(5), login.defs(5),
passwd(5), and shadow(5) manual pages.
22.2.1 Configuring Local Access
You can use the User Manager GUI (system-config-users) to add or delete users and groups and to
modify settings such as passwords, home directories, login shells, and group membership. Alternatively,
you can use commands such as useradd and groupadd.
To enable local access control, select the Enable local access control check box on the Advanced
Options tab of the Authentication Configuration GUI (system-config-authentication). The system
can then read the /etc/security/access.conf file for local user authorization rules that specify login
combinations that the system accepts or refuses.
Figure 22.2 shows the Authentication Configuration GUI with the Advanced Options tab selected.
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Configuring Local Access
Figure 22.2 Authentication Configuration Advanced Options
Alternatively, use the following command:
# authconfig --enablepamaccess --update
Each entry in /etc/security/access.conf takes the form:
permission : users : origins [ except
where:
permission
Set to + or - to grant or deny login respectively.
users
Specifies a space-separated list of user or group names or ALL for any user or group.
Enclose group names in parentheses to distinguish them from user names. You can use
the EXCEPT operator to exclude a list of users from the rule.
origins
Specifies a space-separated list of host names, fully qualified domain names, network
addresses, terminal device names, ALL, or NONE. You can use the EXCEPT operator to
exclude a list of origins from the rule.
For example, the following rule denies login access by anyone except root from the network
192.168.2.0/24:
- : ALL except root : 192.168.2.0/24
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Configuring Fingerprint Reader Authentication
For more information, see the access.conf(5) manual page and Chapter 23, Local Account
Configuration.
22.2.2 Configuring Fingerprint Reader Authentication
If appropriate hardware is installed and supported, the system can use fingerprint scans to authenticate
users.
To enable fingerprint reader support, select the Enable fingerprint reader support check box on the
Advanced Options tab of the Authentication Configuration GUI (system-config-authentication).
Alternatively, use the following command:
# authconfig --enablefingerprint --update
22.2.3 Configuring Smart Card Authentication
If appropriate hardware is installed and supported, the system can use smart cards to authenticate users.
The pam_pkcs11 package provides a PAM login module that enables X.509 certificate-based user
authentication. The module uses the Name Service Switch (NSS) to manage and validate PKCS #11 smart
cards by using locally stored root CA certificates, online or locally accessible certificate revocation lists
(CRLs), and the Online Certificate Status Protocol (OCSP).
To enable smart card authentication:
1. Install the pam_pkcs11 package:
# yum install pam_pkcs11
2. Use the following command to install the root CA certificates in the NSS database:
# certutil -A -d /etc/pki/nssdb -t "TC,C,C" -n "Root CA certificates" -i CACert.pem
where CACert.pem is the base-64 format root CA certificate file.
3. Run the Authentication Configuration GUI:
# system-config-authentication
4. On the Advanced Options tab, select the Enable smart card support check box.
5. If you want to disable all other login authentication methods, select the Require smart card for login
check box.
Caution
Do not select this option until you have tested that can use a smart card to
authenticate with the system.
6. From the Card removal action menu, select the system's response if a user removes a smart card
while logged in to a session:
Ignore
The system ignores card removal for the current session.
Lock
The system locks the user out of the session .
You can also use the following command to configure smart card authentication:
# authconfig --enablesmartcard --update
To specify the system's response if a user removes a smart card while logged in to a session:
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About IPA
authconfig --smartcardaction=0|1 --update
Specify a value of 0 to --smartcardaction to lock the system if a card is removed. To ignore card
removal, use a value of 1.
Once you have tested that you can use a smart card to authenticate with the system, you can disable all
other login authentication methods.
# authconfig --enablerequiresmartcard --update
22.3 About IPA
IPA allows you to set up a domain controller for DNS, Kerberos, and authorization policies as an alternative
to Active Directory Services. You can enrol client machines with an IPA domain so that they can access
information for single sign-on authentication. IPA combines the capabilities of existing well-known
technologies such as certificate services, DNS, LDAP, Kerberos, LDAP, and NTP.
22.3.1 Configuring IPA
To be able to configure IPA authentication, use yum to install the ipa-client and ipa-admintools
packages.
If you use the Authentication Configuration GUI and select IPA v2 as the user account database, you are
prompted to enter the names of the IPA domain, realm, and server. You can also select to configure NTP
so that the system time is consistent with the IPA server. If you have initialized Kerberos, you can click
Join Domain to create a machine account on the IPA server and grant permission to join the domain.
For more information about configuring IPA, see http://freeipa.org/page/Documentation.
22.4 About LDAP Authentication
The Lightweight Directory Access Protocol (LDAP) allows client systems to access information stored on
LDAP servers over a network. An LDAP directory server stores information in a directory-based database
that is optimized for searching and browsing, and which also supports simple functions for accessing and
updating entries in the database.
Database entries are arranged in a hierarchical tree-like structure, where each directory can store
information such as names, addresses, telephone numbers, network service information, printer
information, and many other types of structured data. Systems can use LDAP for authentication, which
allows users to access their accounts from any machine on a network.
The smallest unit of information in an LDAP directory is an entry, which can have one or more attributes.
Each attribute of an entry has a name (also known as an attribute type or attribute description) and one
or more values. Examples of types are domain component (dc), common name (cn), organizational unit
(ou) and email address (mail). The objectClass attribute allows you to specify whether an attribute
is required or optional. An objectClass attribute's value specifies the schema rules that an entry must
obey.
A distinguished name (dn) uniquely identifies an entry in LDAP. The distinguished name consists of the
name of the entry (the relative distinguished name or RDN) concatenated with the names of its ancestor
entries in the LDAP directory hierarchy. For example, the distinguished name of a user with the RDN
uid=arc815 might be uid=arc815,ou=staff,dc=mydom,dc=com.
The following are examples of information stored in LDAP for a user:
# User arc815
dn: uid=arc815,ou=People,dc=mydom,dc=com
cn: John Beck
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About LDAP Data Interchange Format
givenName: John
sn: Beck
uid: arc815
uidNumber: 5159
gidNumber: 626
homeDirectory: /nethome/arc815
loginShell: /bin/bash
mail: [email protected]
objectClass: top
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
userPassword: {SSHA}QYrFtKkqOrifgk8H4EYf68B0JxIIaLga
and for a group:
# Group employees
dn: cn=employees,ou=Groups,dc=mydom,dc=com
cn: employees
gidNumber: 626
objectClass: top
objectClass: posixGroup
memberUid: arc815
memberUid: arc891
22.4.1 About LDAP Data Interchange Format
LDAP data itself is stored in a binary format. LDAP Data Interchange Format (LDIF) is a plain-text
representation of an LDAP entry that allows the import and export LDAP data, usually to transfer the data
between systems, but it also allows you to use a text editor to modify the content.
The data for an entry in an LDIF file takes the form:
[id] dn: distinguished_name
attribute_type: value | [attribute=]value[, [attribute=] value]...
...
objectClass: value
...
The optional id number is determined by the application that you use to edit the entry. Each attribute type
for an entry contains either a value or a comma-separated list of attribute and value pairs as defined in the
LDAP directory schema.
There must be a blank line between each dn definition section or include: line. There must not be any
other blank lines or any white space at the ends of lines. White space at the start of a line indicates a
continuation of the previous line.
22.4.2 Configuring an LDAP Server
OpenLDAP is an open-source implementation of LDAP that allows you configure an LDAP directory server.
To configure a system as an LDAP server:
1. Install the OpenLDAP packages:
# yum install openldap openldap-servers openldap-clients nss-pam-ldapd
The OpenLDAP configuration is stored in the following files below /etc/openldap:
ldap.conf
The configuration file for client applications.
slapd.d/cn=config.ldif
The default global configuration LDIF file for OpenLDAP.
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Configuring an LDAP Server
slapd.d/cn=config/*.ldif
Configuration LDIF files for the database and schema.
slapd.d/cn=config/
cn=schema/*.ldif
Schema configuration LDIF files. More information about the
OpenLDAP schema is available at http://www.openldap.org/doc/
admin/schema.html.
Note
You should never need to edit any files under /etc/openldap/slapd.d as
you can reconfigure OpenLDAP while the slapd service is running.
2. If you want configure slapd to listen on port 636 for connections over an SSL tunnel (ldaps://), edit
/etc/sysconfig/ldap, and change the value of SLAPD_LDAPS to yes:
SLAPD_LDAPS=yes
If required, you can prevent slapd listening on port 389 for ldap:// connections, by changing the
value of SLAPD_LDAP to no:
SLAPD_LDAP=no
3. Allow incoming TCP connections on port 389 from the local network:
# iptables -I INPUT -s subnet_addr/prefix_length -p tcp \
-m state --state NEW -m tcp –dport 389 -j ACCEPT
# service iptables save
where subnet_addr/prefix_length specifies the network address, for example
192.168.2.0/24.
The primary TCP port for LDAP is 389. If you configure LDAP to use an SSL tunnel (ldaps), substitute
the port number that the tunnel uses, which is usually 636, for example:
# iptables -I INPUT -s subnet_addr/prefix_length -p tcp \
-m state --state NEW -m tcp -–dport 636 -j ACCEPT
# service iptables save
Add similar rules for other networks from which LDAP clients can connect.
4. Change the user and group ownership of /var/lib/ldap and any files that it contains to ldap:
# cd /var/lib/ldap
# chown ldap:ldap ./*
5. Start the slapd service and configure it to start following system reboots:
# service slapd start
# chkconfig slapd on
6. Generate a hash of the LDAP password that you will use with the olcRootPW entry in the configuration
file for your domain database, for example:
# slappasswd -h {SSHA}
New password: password
Re-enter new password: password
{SSHA}lkMShz73MZBic19Q4pfOaXNxpLN3wLRy
7. Create an LDIF file with a name such as config-mydom-com.ldif that contains configuration
entries for your domain database based on the following example:
# Load the schema files required for accounts
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Configuring an LDAP Server
include file:///etc/ldap/schema/cosine.ldif
include file:///etc/ldap/schema/nis.ldif
include file:///etc/ldap/schema/inetorgperson.ldif
# Load the HDB (hierarchical database) backend modules
dn: cn=module,cn=config
objectClass: olcModuleList
cn: module
olcModulepath: /usr/lib/ldap
olcModuleload: back_hdb
# Configure the database settings
dn: olcDatabase=hdb,cn=config
objectClass: olcDatabaseConfig
objectClass: olcHdbConfig
olcDatabase: {1}hdb
olcSuffix: dc=mydom,dc=com
# The database directory must already exist
# and it should only be owned by ldap:ldap.
# Setting its mode to 0700 is recommended
olcDbDirectory: /var/lib/ldap
olcRootDN: cn=admin,dc=mydom,dc=com
olcRootPW: {SSHA}lkMShz73MZBic19Q4pfOaXNxpLN3wLRy
olcDbConfig: set_cachesize 0 10485760 0
olcDbConfig: set_lk_max_objects 2000
olcDbConfig: set_lk_max_locks 2000
olcDbConfig: set_lk_max_lockers 2000
olcDbIndex: objectClass eq
olcLastMod: TRUE
olcDbCheckpoint: 1024 10
# Set up access control
olcAccess: to attrs=userPassword
by dn="cn=admin,dc=mydom,dc=com"
write by anonymous auth
by self write
by * none
olcAccess: to attrs=shadowLastChange
by self write
by * read
olcAccess: to dn.base=""
by * read
olcAccess: to *
by dn="cn=admin,dc=mydom,dc=com"
write by * read
Note
This configuration file allows you to reconfigure slapd while it is running. If you
use a slapd.conf configuration file, you can also update slapd dynamically,
but such changes do not persist if you restart the server.
For more information, see the slapd-config(5) manual page.
8. Use the ldapadd command to add the LDIF file:
# ldapadd -Y EXTERNAL -H ldapi:/// -f config-mydom-com.ldif
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
adding new entry "cn=module,cn=config"
adding new entry "olcDatabase=hdb,cn=config"
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Replacing the Default Certificates
For more information about configuring OpenLDAP, see the slapadd(8C), slapd(8C), slapdconfig(5), and slappasswd(8C) manual pages, the OpenLDAP Administrator’s Guide (/usr/share/
doc/openldap-servers-version/guide.html), and the latest OpenLDAP documentation at http://
www.openldap.org/doc/.
22.4.3 Replacing the Default Certificates
If you configure LDAP to use Transport Layer Security (TLS) or Secure Sockets Layer (SSL) to secure
the connection to the LDAP server, you need a public certificate that clients can download. You can
obtain certificates from a Certification Authority (CA) or you can use the openssl command to create the
certificate. See Section 22.4.4, “Creating and Distributing Self-signed CA Certificates”.
Once you have a server certificate, its corresponding private key file, and a root CA certificate, you can
replace the default certificates that are installed in /etc/openldap/certs.
To display the existing certificate entries that slapd uses with TLS, use the ldapsearch command:
# ldapsearch -LLL -Y EXTERNAL -H ldapi:/// -b "cn=config" \
olcTLSCACertificatePath olcTLSCertificateFile olcTLSCertificateKeyFile
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
dn: cn=config
olcTLSCACertificatePath: /etc/openldap/certs
olcTLSCertificateFile: "OpenLDAP Server"
olcTLSCertificateKeyFile: /etc/openldap/certs/password
...
To replace the TLS attributes in the LDAP configuration:
1. Create an LDIF file that defines how to modify the attributes, for example:
dn: cn=config
changetype: modify
delete: olcTLSCACertificatePath
# Omit the following clause for olcTLSCACertificateFile
# if you do not have a separate root CA certificate
dn: cn=config
changetype: modify
add: olcTLSCACertificateFile
olcTLSCACertificateFile: /etc/ssl/certsCAcert.pem
dn: cn=config
changetype: modify
replace: olcTLSCertificateFile
olcTLSCertificateFile: /etc/ssl/certs/server-cert.pem
dn: cn=config
changetype: modify
replace: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/ssl/certs/server-key.pem
dn: cn=config
changetype: modify
add: olcTLSCipherSuite
olcTLSCipherSuite: TLSv1+RSA:!NULL
dn: cn=config
changetype: modify
add: olcTLSVerifyClient
olcTLSVerifyClient: never
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Creating and Distributing Self-signed CA Certificates
If you generate only a self-signed certificate and its corresponding key file, you do not need to specify a
root CA certificate.
2. Use the ldapmodify command to apply the LDIF file:
# ldapmodify -Y EXTERNAL -H ldapi:/// -f mod-TLS.ldif
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
modifying entry "cn=config"
modifying entry "cn=config"
modifying entry "cn=config"
...
3. Verify that the entries have changed:
# ldapsearch -LLL -Y EXTERNAL -H ldapi:/// -b "cn=config" \
olcTLSCACertificatePath olcTLSCertificateFile olcTLSCertificateKeyFile
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
dn: cn=config
olcTLSCACertificateFile: /etc/ssl/certs/CAcert.pem
olcTLSCertificateFile: /etc/ssl/certs/server-cert.pem
olcTLSCertificateKeyFile: /etc/ssl/certs/server-key.pem
olcTLSCipherSuite: TLSv1+RSA:!NULL
olcTLSVerifyClient: never
...
4. Restart the slapd service to make it use the new certificates:
# service slapd restart
For more information, see the ldapmodify(1), ldapsearch(1) and openssl(1) manual pages.
22.4.4 Creating and Distributing Self-signed CA Certificates
For usage solely within an organization, you might want to create certificates that you can use with LDAP.
There are a number of ways of creating suitable certificates, for example:
• Create a self-signed CA certificate together with a private key file.
• Create a self-signed root CA certificate and private key file, and use the CA certificate and its key file to
sign a separate server certificate for each server.
The following procedure describes how to use openssl to create a self-signed CA certificate and private
key file, and then use these files to sign server certificates.
To create the CA certificate and use it to sign a server certificate:
1. Change directory to /etc/openldap/certs on the LDAP server:
# cd /etc/openldap/certs
2. Create the private key file CAcert-key.pem for the CA certificate:
# openssl genrsa -out CAcert-key.pem 1024
Generating RSA private key, 1024 bit long modulus
......++++++
....++++++
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Creating and Distributing Self-signed CA Certificates
e is 65537 (0x10001)
3. Change the mode on the key file to 0400:
# chmod 0400 CAcert-key.pem
4. Create the certificate request CAcert.csr:
# openssl req -new -key CAcert-key.pem -out CAcert.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
----Country Name (2 letter code) [XX]:US
State or Province Name (full name) []:California
Locality Name (eg, city) [Default City]:Redwood City
Organization Name (eg, company) [Default Company Ltd]:Mydom Inc
Organizational Unit Name (eg, section) []:Org
Common Name (eg, your name or your server's hostname) []:www.mydom.org
Email Address []:[email protected]
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:<Enter>
An optional company name []:<Enter>
5. Create a CA certificate that is valid for approximately three years:
# openssl x509 -req -days 1095 -in CAcert.csr -signkey CAcert-key.pem -out CAcert.pem
rt-key.pem -out CAcert.pem
Signature ok
subject=/C=US/ST=California/L=Redwood City/O=Mydom
[email protected]
Getting Private key
6. For each server certificate that you want to create:
a. Create the private key for the server certificate:
# openssl genrsa -out server-key.pem 1024
Generating RSA private key, 1024 bit long modulus
.............++++++
...........................++++++
e is 65537 (0x10001)
Note
If you intend to generate server certificates for several servers, name the
certificate, its key file, and the certificate request so that you can easily
identify both the server and the service, for example, ldap_host02cert.pem, ldap_host02-key.pem, and ldap_host02-cert.csr.
b. Change the mode on the key file to 0400, and change its user and group ownership to ldap:
# chmod 0400 server-key.pem
# chown ldap:ldap server-key.pem
c. Create the certificate request server-cert.csr:
# openssl req -new -key server-key.pem -out server-cert.csr
You are about to be asked to enter information that will be incorporated
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Creating and Distributing Self-signed CA Certificates
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
----Country Name (2 letter code) [XX]:US
State or Province Name (full name) []:California
Locality Name (eg, city) [Default City]:Redwood City
Organization Name (eg, company) [Default Company Ltd]:Mydom Inc
Organizational Unit Name (eg, section) []:Org
Common Name (eg, your name or your server's hostname) []:ldap.mydom.com
Email Address []:[email protected]
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:<Enter>
An optional company name []:<Enter>
Note
For the Common Name, specify the Fully Qualified Domain Name (FQDN)
of the server. If the FQDN of the server does not match the common name
specified in the certificate, clients cannot obtain a connection to the server.
d. Use the CA certificate and its corresponding key file to sign the certificate request and generate the
server certificate:
# openssl x509 -req -days 1095 -CAcreateserial \
-in server-cert.csr -CA CAcert.pem -CAkey CAcert-key.pem \
-out server-cert.pem
Signature ok
subject=/C=US/ST=California/L=Redwood City/O=Mydom
[email protected]
Getting CA Private Key
7. If you generate server certificates for other LDAP servers, copy the appropriate server certificate, its
corresponding key file, and the CA certificate to /etc/openldap/certs on those servers.
8. Set up a web server to host the CA certificate for access by clients. The following steps assume that
the LDAP server performs this function. You can use any suitable, alternative server instead.
a. Install the Apache HTTP server.
# yum install httpd
b. Create a directory for the CA certificate under /var/www/html, for example:
# mkdir /var/www/html/certs
c. Copy the CA certificate to /var/www/html/certs.
# cp CAcert.pem /var/www/html/certs
Caution
Do not copy the key files.
d. Edit the HTTP server configuration file, /etc/httpd/conf/httpd.conf, and specify the
resolvable domain name of the server in the argument to ServerName.
ServerName server_addr:80
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Initializing an Organization in LDAP
If the server does not have a resolvable domain name, enter its IP address instead.
Verify that the setting of the Options directive in the <Directory "/var/www/html"> section
specifies Indexes and FollowSymLinks to allow you to browse the directory hierarchy, for
example:
Options Indexes FollowSymLinks
e. Start the Apache HTTP server, and configure it to start after a reboot.
# service httpd start
# chkconfig httpd on
f.
If you have enabled a firewall on your system, configure it to allow incoming HTTP connection
requests on TCP port 80.
For example, the following command configures iptables to allow incoming HTTP connection
requests and saves the change to the firewall configuration:
# iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
# service iptables save
22.4.5 Initializing an Organization in LDAP
Before you can define people, groups, servers, printers, and other entitles for your organization, you must
first set up information in LDAP for the organization itself.
To define an organization in LDAP:
1. Create an LDIF file that defines the organization, for example mydom-com-organization.ldif:
# Organization mydom.com
dn: dc=mydom,dc=com
dc: mydom
objectclass: dcObject
objectclass: organizationalUnit
ou: mydom.com
# Users
dn: ou=People,dc=mydom,dc=com
objectClass: organizationalUnit
ou: people
# Groups
dn: ou=Groups,dc=mydom,dc=com
objectClass: organizationalUnit
ou: groups
2. If you have configured LDAP authentication, use the ldapadd command to add the organization to
LDAP:
# ldapadd -cxWD "cn=admin,dc=mydom,dc=com" -f mydom-com-organization.ldif
Enter LDAP Password: admin_password
adding new entry "dc=mydom,dc=com"
adding new entry "ou=People,dc=mydom,dc=com"
adding new entry "ou=Groups,dc=mydom,dc=com"
If you have configured Kerberos authentication, use kinit to obtain a ticket granting ticket (TGT) for
the admin principal, and use this form of the ldapadd command:
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Adding an Automount Map to LDAP
# ldapadd -f mydom-com-organization.ldif
For more information, see the ldapadd(1) manual page.
22.4.6 Adding an Automount Map to LDAP
You can make an automount map such as auto.home available in LDAP so that the automounter mounts
a user's home directory on demand.
To add the auto.home map to LDAP:
1. Create an LDIF file that defines entries for the map's name and its contents, for example autohome.ldif:
dn: nisMapName=auto.home,dc=mydom,dc=com
objectClass: top
objectClass: nisMap
nisMapName: auto.home
dn: cn=*,nisMapName=auto.home,dc=mydom,dc=com
objectClass: nisObject
cn: *
nisMapEntry: -rw,sync nfssvr:/nethome/&
nisMapName: auto.home
where nfssvr is the host name or IP address of the NFS server that exports the users' home
directories.
2. If you have configured LDAP authentication, use the following command to add the map to LDAP:
# ldapadd -xcWD "cn=admin,dc=mydom,dc=com" \
-f auto-home.ldif
Enter LDAP Password: user_password
adding new entry "nisMapName=auto.home,dc=mydom,dc=com"
adding new entry "cn=*,nisMapName=auto.home,dc=mydom,dc=com"
If you have configured Kerberos authentication, use kinit to obtain a ticket granting ticket (TGT) for
the admin principal, and use this form of the command:
# ldapmodify -f auto-home.ldif
3. Verify that the map appears in LDAP:
# ldapsearch -LLL -x -b "dc=mydom,dc=com" nisMapName=auto.home
dn: nisMapName=auto.home,dc=mydom,dc=com
objectClass: top
objectClass: nisMap
nisMapName: auto.home
dn: cn=*,nisMapName=auto.home,dc=mydom,dc=com
objectClass: nisObject
cn: *
nisMapEntry: -rw,sync nfssvr.mydom.com:/nethome/&
nisMapName: auto.home
22.4.7 Adding a Group to LDAP
If you configure users in user private groups (UPGs), define that group along with the user. See
Section 22.4.8, “Adding a User to LDAP”.
To add a group to LDAP:
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Adding a User to LDAP
1. Create an LDIF file that defines the group, for example employees-group.ldif:
# Group employees
dn: cn=employees,ou=Groups,dc=mydom,dc=com
cn: employees
gidNumber: 626
objectClass: top
objectclass: posixGroup
2. If you have configured LDAP authentication, use the following command to add the group to LDAP:
# ldapadd -cxWD "cn=admin,dc=mydom,dc=com" -f employees-group.ldif
Enter LDAP Password: admin_password
adding new entry "cn=employees,ou=Groups,dc=mydom,dc=com"
If you have configured Kerberos authentication, use kinit to obtain a ticket granting ticket (TGT) for
the admin principal, and use this form of the ldapadd command:
# ldapadd -f employees-group.ldif
3. Verify that you can locate the group in LDAP:
# ldapsearch -LLL -x -b "dc=mydom,dc=com" gidNumber=626
dn: cn=employees,ou=Groups,dc=mydom,dc=com
cn: employees
gidNumber: 626
objectClass: top
objectClass: posixGroup
For more information, see the ldapadd(1) and ldapsearch(1) manual pages.
22.4.8 Adding a User to LDAP
Note
This procedure assumes that:
• LDAP provides information for ou=People, ou=Groups, and
nisMapName=auto.home.
• The LDAP server uses NFS to export the users' home directories. See
Section 20.2.2, “Mounting an NFS File System”
To create an account for a user on the LDAP server:
1. If the LDAP server does not already export the base directory of the users' home directories, perform
the following steps on the LDAP server:
a. Create the base directory for user directories, for example /nethome:
# mkdir /nethome
b. Add an entry such as the following to /etc/exports:
/nethome
*(rw,sync)
You might prefer to restrict which clients can mount the file system. For example, the following entry
allows only clients in the 192.168.1.0/24 subnet to mount /nethome:
/nethome
192.168.1.0/24(rw,sync)
c. Use the following command to export the file system:
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Adding a User to LDAP
# exportfs -i -o ro,sync *:/nethome
2. Create the user account, but do not allow local logins:
# useradd -b base_dir -s /sbin/nologin -u UID -U username
For example:
# useradd -b /nethome -s /sbin/nologin -u 5159 -U arc815
The command updates the /etc/passwd file and creates a home directory under /nethome on the
LDAP server.
The user's login shell will be overridden by the LoginShell value set in LDAP.
3. Use the id command to list the user and group IDs that have been assigned to the user, for example:
# id arc815
uid=5159(arc815) gid=5159(arc815) groups=5159(arc815)
4. Create an LDIF file that defines the user, for example arc815-user.ldif:
# UPG arc815
dn: cn=arc815,ou=Groups,dc=mydom,dc=com
cn: arc815
gidNumber: 5159
objectclass: top
objectclass: posixGroup
# User arc815
dn: uid=arc815,ou=People,dc=mydom,dc=com
cn: John Beck
givenName: John
sn: Beck
uid: arc815
uidNumber: 5159
gidNumber: 5159
homeDirectory: /nethome/arc815
loginShell: /bin/bash
mail: [email protected]
objectClass: top
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
userPassword: {SSHA}x
In this example, the user belongs to a user private group (UPG), which is defined in the same file.
The user’s login shell attribute LoginShell is set to /bin/bash. The user's password attribute
userPassword is set to a placeholder value. If you use Kerberos authentication with LDAP, this
attribute is not used.
5. If you have configured LDAP authentication, use the following command to add the user to LDAP:
# ldapadd -cxWD cn=admin,dc=mydom,dc=com -f arc815-user.ldif
Enter LDAP Password: admin_password
adding new entry "cn=arc815,ou=Groups,dc=mydom,dc=com"
adding new entry "uid=arc815,ou=People,dc=mydom,dc=com"
If you have configured Kerberos authentication, use kinit to obtain a ticket granting ticket (TGT) for
the admin principal, and use this form of the ldapadd command:
# ldapadd -f arc815-user.ldif
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Adding Users to a Group in LDAP
6. Verify that you can locate the user and his or her UPG in LDAP:
# ldapsearch -LLL -x -b "dc=mydom,dc=com" '(|(uid=arc815)(cn=arc815))'
dn: cn=arc815,ou=Groups,dc=mydom,dc=com
cn: arc815
gidNumber: 5159
objectClass: top
objectClass: posixGroup
dn: uid=arc815,ou=People,dc=mydom,dc=com
cn: John Beck
givenName: John
sn: Beck
uid: arc815
uidNumber: 5159
gidNumber: 5159
homeDirectory: /home/arc815
loginShell: /bin/bash
mail: [email protected]
objectClass: top
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
7. If you have configured LDAP authentication, set the user password in LDAP:
# ldappasswd -xWD "cn=admin,dc=mydom,dc=com" \
-S "uid=arc815,ou=people,dc=mydom,dc=com"
New password: user_password
Re-enter new password: user_password
Enter LDAP Password: admin_password
If you have configured Kerberos authentication, use kinit to obtain a ticket granting ticket (TGT) for
the admin principal, and use the kadmin command to add the user (principal) and password to the
database for the Kerberos domain, for example:
# kadmin -q "addprinc [email protected]"
For more information, see the kadmin(1), ldapadd(1), ldappasswd(1), and ldapsearch(1)
manual pages.
22.4.9 Adding Users to a Group in LDAP
To add users to an existing group in LDAP:
1. Create an LDIF file that defines the users that should be added to the memberuid attribute for the
group, for example employees-add-users.ldif:
dn: cn=employees,ou=Groups,dc=mydom,dc=com
changetype: modify
add: memberUid
memberUid: arc815
dn: cn=employees,ou=Groups,dc=mydom,dc=com
changetype: modify
add: memberUid
memberUid: arc891
...
2. If you have configured LDAP authentication, use the following command to add the group to LDAP:
# ldapmodify -xcWD "cn=admin,dc=mydom,dc=com" \
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Enabling LDAP Authentication
-f employees-add-users.ldif
Enter LDAP Password: user_password
modifying entry "cn=employees,ou=Groups,dc=mydom,dc=com"
...
If you have configured Kerberos authentication, use kinit to obtain a ticket granting ticket (TGT) for
the admin principal, and use this form of the command:
# ldapmodify -f employees-add-users.ldif
3. Verify that the group has been updated in LDAP:
# ldapsearch -LLL -x -b "dc=mydom,dc=com" gidNumber=626
dn: cn=employees,ou=Groups,dc=mydom,dc=com
cn: employees
gidNumber: 626
objectClass: top
objectClass: posixGroup
memberUid: arc815
memberUid: arc891
...
22.4.10 Enabling LDAP Authentication
To enable LDAP authentication for an LDAP client by using the Authentication Configuration GUI:
1. Install the openldap-clients package:
# yum install openldap-clients
2. Run the Authentication Configuration GUI:
# system-config-authentication
3. Select LDAP as the user account database and enter values for:
LDAP Search Base DN
The LDAP Search Base DN for the database. For example:
dc=mydom,dc=com.
LDAP Server
The URL of the LDAP server including the port number. For example,
ldap://ldap.mydom.com:389 or ldaps://ldap.mydom.com:636.
LDAP authentication requires that you use either LDAP over SSL (ldaps) or Transport Layer Security
(TLS) to secure the connection to the LDAP server.
4. If you use TLS, click Download CA Certificate and enter the URL from which to download the CA
certificate that provides the basis for authentication within the domain.
5. Select either LDAP password or Kerberos password for authentication.
6. If you select Kerberos authentication, enter values for:
Realm
The name of the Kerberos realm.
KDCs
A comma-separated list of Key Distribution Center (KDC) servers that can issue
Kerberos ticket granting tickets and service tickets.
Admin Servers
A comma-separated list of Kerberos administration servers.
Alternatively, you can use DNS to configure these settings:
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Enabling LDAP Authentication
• Select the Use DNS to resolve hosts to realms check box to look up the name of the realm defined
as a TXT record in DNS, for example:
_kerberos.mydom.com
IN TXT "MYDOM.COM"
• Select the Use DNS to locate KDCs for realms check box to look up the KDCs and administration
servers defined as SVR records in DNS, for example:
_kerberos._tcp.mydom.com
_kerberos._udp.mydom.com
_kpasswd._udp.mydom.com
_kerberos-adm._tcp.mydom.com
IN
IN
IN
IN
SVR
SVR
SVR
SVR
1
1
1
1
0
0
0
0
88
88
464
749
krbsvr.mydom.com
krbsvr.mydom.com
krbsvr.mydom.com
krbsvr.mydom.com
7. Click Apply to save your changes.
Figure 22.3 shows the Authentication Configuration GUI with LDAP selected for the user account database
and for authentication.
Figure 22.3 Authentication Configuration Using LDAP
You can also enable LDAP by using the authconfig command.
To use LDAP as the authentication source, specify the --enableldapauth option together with the full
LDAP server URL including the port number and the LDAP Search Base DN, as shown in the following
example:.
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Enabling LDAP Authentication
# authconfig --enableldap --enableldapauth \
--ldapserver=ldaps://ldap.mydom.com:636 \
--ldapbasedn="ou=people,dc=mydom,dc=com" \
--update
If you want to use TLS, additionally specify the --enableldaptls option and the download URL of the
CA certificate, for example:
# authconfig --enableldap --enableldapauth \
--ldapserver=ldap://ldap.mydom.com:389 \
--ldapbasedn="ou=people,dc=mydom,dc=com" \
--enableldaptls \
--ldaploadcacert=https://ca-server.mydom.com/CAcert.pem \
--update
The --enableldap option configures /etc/nsswitch.conf to enable the system to use LDAP
and SSSD for information services. The --enableldapauth option enables LDAP authentication by
modifying the PAM configuration files in /etc/pam.d to use the pam_ldap.so module.
For more information, see the authconfig(8), pam_ldap(5), and nsswitch.conf(5) manual pages.
For information about using Kerberos authentication with LDAP, see Section 22.6.3, “Enabling Kerberos
Authentication”.
Note
You must also configure SSSD to be able to access information in LDAP. See
Section 22.4.10.1, “Configuring an LDAP Client to use SSSD”.
If your client uses automount maps stored in LDAP, you must configure autofs
to work with LDAP. See Section 22.4.10.2, “Configuring an LDAP Client to Use
Automount Maps”.
22.4.10.1 Configuring an LDAP Client to use SSSD
The Authentication Configuration GUI and authconfig configure access to LDAP via sss entries in /
etc/nsswitch.conf so you must configure the System Security Services Daemon (SSSD) on the LDAP
client.
To configure an LDAP client to use SSSD:
1. Install the sssd and sssd-client packages:
# yum install sssd sssd-client
2. Edit the /etc/sssd/sssd.conf configuration file and configure the sections to support the required
services, for example:
[sssd]
config_file_version = 2
domains = default
services = nss, pam
[domain/default]
id_provider = ldap
ldap_uri = ldap://ldap.mydom.com
ldap_id_use_start_tls = true
ldap_search_base = dc=mydom,dc=com
ldap_tls_cacertdir = /etc/openldap/cacerts
auth_provider = krb5
chpass_provider = krb5
krb5_realm = MYDOM.COM
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Enabling LDAP Authentication
krb5_server = krbsvr.mydom.com
krb5_kpasswd = krbsvr.mydom.com
cache_credentials = true
[domain/LDAP]
id_provider = ldap
ldap_uri = ldap://ldap.mydom.com
ldap_search_base = dc=mydom,dc=com
auth_provider = krb5
krb5_realm = MYDOM.COM
krb5_server = kdcsvr.mydom.com
cache_credentials = true
min_id = 5000
max_id = 25000
enumerate = false
[nss]
filter_groups = root
filter_users = root
reconnection_retries = 3
entry_cache_timeout = 300
[pam]
reconnection_retries = 3
offline_credentials_expiration = 2
offline_failed_login_attempts = 3
offline_failed_login_delay = 5
3. Change the mode of /etc/sssd/sssd.conf to 0600:
# chmod 0600 /etc/sssd/sssd.conf
4. Enable the SSSD service:
# authconfig --update --enablesssd –-enablesssdauth
For more information, see the sssd.conf(5) manual page and Section 22.8, “About the System Security
Services Daemon”.
22.4.10.2 Configuring an LDAP Client to Use Automount Maps
If you have configured an automount map for auto.home in LDAP, you can configure an LDAP client to
mount the users' home directories when they log in.
To configure an LDAP client to automount users' home directories:
1. Install the autofs package:
# yum install autofs
2. Verify that the auto.home map is available :
# ldapsearch -LLL -x -b "dc=mydom,dc=com" nisMapName=auto.home
dn: nisMapName=auto.home,dc=mydom,dc=com
objectClass: top
objectClass: nisMap
nisMapName: auto.home
dn: cn=*,nisMapName=auto.home,dc=mydom,dc=com
objectClass: nisObject
cn: *
nisMapEntry: -rw,sync nfssvr.mydom.com:/nethome/&
nisMapName: auto.home
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About NIS Authentication
In this example, the map is available. For details of how to make this map available, see Section 22.4.6,
“Adding an Automount Map to LDAP”.
3. If the auto.home map is available, edit /etc/auto.master and create an entry that tells autofs
where to find the auto.home map in LDAP, for example:
/nethome
ldap:nisMapName=auto.home,dc=mydom,dc=com
If you use LDAP over SSL, specify ldaps: instead of ldap:.
4. Edit /etc/autofs_ldap_auth.conf and configure the authentication settings for autofs with
LDAP, for example:
<autofs_ldap_sasl_conf
usetls="yes"
tlsrequired="no"
authrequired="autodetect"
authtype="GSSAPI"
clientprinc="[email protected]"
/>
This example assumes that Kerberos authentication with the LDAP server uses TLS for the connection.
The principal for the client system must exist in the Kerberos database. You can use the klist -k
command to verify this. If the principal for the client does not exist, use kadmin to add the principal.
5. If you use Kerberos Authentication, use kadmin to add a principal for the LDAP service on the LDAP
server, for example:
# kadmin -q "addprinc [email protected]
6. Restart the autofs service, and configure the service to start following a system reboot:
# service autofs restart
# chkconfig autofs on
The autofs service creates the directory /nethome. When a user logs in, the automounter mounts
his or her home directory under /nethome.
If the owner and group for the user's files are unexpectedly listed as the anonymous user or group
(nobody or nogroup) and all_squash has not been specified as a mount option, verify that the
Domain setting in /etc/idmapd.conf on the NFS server is set to the DNS domain name. Restart the
NFS services on the NFS server if you change this file.
For more information, see the auto.master(5) and autofs_ldap_auth.conf(5) manual pages.
22.5 About NIS Authentication
NIS stores administrative information such as user names, passwords, and host names on a centralized
server. Client systems on the network can access this common data. This configuration allows to move
from machine to machine without having to remember different passwords and copy data from one
machine to another. Storing administrative information centrally, and providing a means of accessing it
from networked systems, also ensures the consistency of that data. NIS also reduces the overhead of
maintaining administration files such as /etc/passwd on each system.
A network of NIS systems is an NIS domain. Each system within the domain has the same NIS domain
name, which is different from a DNS domain name. The DNS domain is used throughout the Internet to
refer to a group of systems. an NIS domain is used to identify systems that use files on an NIS server. an
NIS domain must have exactly one master server but can have multiple slave servers.
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About NIS Maps
22.5.1 About NIS Maps
The administrative files within an NIS domain are NIS maps, which are dbm-format files that you generate
from existing configuration files such as /etc/passwd, /etc/shadow, and /etc/groups. Each map
is indexed on one field, and records are retrieved by specifying a value from that field. Some source files
such as /etc/passwd have two maps:
passwd.byname
Indexed on user name.
passwd.byuid
Indexed on user ID.
The /var/yp/nicknames file contains a list of commonly used short names for maps such as passwd
for passwd.byname and group for group.byname.
You can use the ypcat command to display the contents of an NIS map, for example:
# ypcat - passwd | grep 500
guest:$6$gMIxsr3W$LaAo...6EE6sdsFPI2mdm7/NEm0:500:500::/nethome/guest:/bin/bash
Note
As the ypcat command displays password hashes to any user, this example
demonstrates that NIS authentication is inherently insecure against password-hash
cracking programs. If you use Kerberos authentication, you can configure password
hashes not to appear in NIS maps, although other information that ypcat displays
could also be useful to an attacker.
For more information, see the ypcat(1) manual page.
22.5.2 Configuring an NIS Server
NIS master servers act as a central, authoritative repository for NIS information. NIS slave servers act
as mirrors of this information. There must be only one NIS master server in an NIS domain. The number
of NIS slave servers is optional, but creating at least one slave server provides a degree of redundancy
should the master server be unavailable.
To configure an NIS master or slave server:
1. Install the ypserv package:
# yum install ypserv
2. Edit /etc/sysconfig/network and add an entry to define the NIS domain, for example:
NISDOMAIN=mynisdom
3. Edit /etc/ypserv.conf to configure NIS options and to add rules for which hosts and domains can
access which NIS maps.
For example, the following entries allow access only to NIS clients in the mynisdom domain on the
192.168.1 subnet:
192.168.1.0/24: mynisdom : * : none
* : * : * : deny
For more information, see the ypserv.conf(5) manual page and the comments in /etc/
ypserv.conf.
4. Create the file /var/yp/securenets and add entries for the networks for which the server should
respond to requests, for example:
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Configuring an NIS Server
# cat > /var/yp/securenets <<!
255.255.255.255 127.0.0.1
255.255.255.0
192.168.1.0
!
# cat /var/yp/securenets
255.255.255.255 127.0.0.1
255.255.255.0
192.168.1.0
In this example, the server accepts requests from the local loopback interface and the 192.168.1
subnet.
5. Edit /var/yp/Makefile:
a. Set any required map options and specify which NIS maps to create using the all target, for
example:
all:
passwd group auto.home
# hosts rpc services netid protocols mail \
# netgrp shadow publickey networks ethers bootparams printcap \
# amd.home auto.local. passwd.adjunct \
# timezone locale netmasks
This example allows NIS to create maps for the /etc/passwd, /etc/group, and /etc/
auto.home files. By default, the information from the /etc/shadow file is merged with the
passwd maps, and the information from the /etc/gshadow file is merged with the group maps.
For more information, see the comments in /var/yp/Makefile.
b. If you intend to use Kerberos authentication instead of NIS authentication, change the values of
MERGE_PASSWD and MERGE_GROUP to false:
MERGE_PASSWD=false
MERGE_GROUP=false
Note
These settings prevent password hashes from appearing in the NIS maps.
c. If you configure any NIS slave servers in the domain, set the value of NOPUSH to false:
NOPUSH=false
If you update the maps, this setting allows the master server to automatically push the maps to the
slave servers.
6. Configure the NIS services:
a. Start the ypserv service and configure it to start after system reboots:
# service ypserv start
# chkconfig ypserv on
The ypserv service runs on the NIS master server and any slave servers.
b. If the server will act as the master NIS server and there will be at least one slave NIS server, start
the ypxfrd service and configure it to start after system reboots:
# service ypxfrd start
# chkconfig ypxfrd on
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Configuring an NIS Server
The ypxfrd service speeds up the distribution of very large NIS maps from an NIS master to any
NIS slave servers. The service runs on the master server only, and not on any slave servers. You
do not need to start this service if there are no slave servers.
c. Start the yppasswdd service and configure it to start after system reboots:
# service yppasswdd start
# chkconfig yppasswdd on
The yppasswdd service allows NIS users to change their password in the shadow map. The
service runs on the NIS master server and any slave servers.
7. Configure the firewall settings:
a. Edit /etc/sysconfig/network and add the following entries that define the ports on which the
ypserv and ypxfrd services listen:
YPSERV_ARGS="-p 834"
YPXFRD_ARGS="-p 835"
These entries fix the ports on which ypserv and ypxfrd listen.
b. Allow incoming TCP connections to ports 111 and 834 and incoming UDP datagrams on ports 111
and 834 from the local network:
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m state --state NEW -m tcp -–dport 111 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m state --state NEW -m tcp -–dport 834 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m udp -–dport 111 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m udp -–dport 834 -j ACCEPT
# service iptables save
tcp \
tcp \
udp \
udp \
where subnet_addr/prefix_length specifies the network address, for example
192.168.1.0/24.
portmapper services requests on TCP port 111 and UDP port 111, and ypserv services requests
on TCP port 834 and UDP port 834.
c. On the master server, if you run the ypxfrd service to support transfers to slave servers, allow
incoming TCP connections to port 835 and incoming UDP datagrams on port 835 from the local
network:
# iptables -I INPUT -s subnet_addr/prefix_length -p tcp \
-m state --state NEW -m tcp -–dport 835 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p udp \
-m udp -–dport 835 -j ACCEPT
# service iptables save
d. Allow incoming UDP datagrams from the local network on the port on which yppasswdd listens:
# iptables -I INPUT -s subnet_addr/prefix_length -p udp \
-m udp -–dport `rpcinfo -p | gawk '/yppasswdd/ {print $4}'` -j ACCEPT
Note
Do not save this rule. The UDP port number that yppasswdd uses is
different every time that it restarts.
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Configuring an NIS Server
e. Edit /etc/rc.local and add the following line:
iptables -I INPUT -s subnet_addr/prefix_length -p udp \
-m udp -–dport `rpcinfo -p | gawk '/yppasswd/ {print $4}'` -j ACCEPT
This entry creates a firewall rule for the yppasswdd service when the system reboots. If you
restart yppasswdd, you must correct the iptables rules manually unless you modify the /etc/
init.d/yppasswdd script.
8. After you have started all the servers, create the NIS maps on the master NIS server:
# /usr/lib64/yp/ypinit -m
At this point, we have to construct a list of the hosts which will run NIS
servers. nismaster is in the list of NIS server hosts. Please continue to add
the names for the other hosts, one per line. When you are done with the
list, type a <control D>."
next host to add: nismaster
next host to add: nisslave1
next host to add: nisslave2
next host to add: ^D
The current list of NIS servers looks like this:
nismaster
nisslave1
nisslave2
Is this correct? [y/n: y] y
We need a few minutes to build the databases...
...
localhost has been set up as a NIS master server.
Now you can run ypinit -s nismaster on all slave server.
Enter the host names of the NIS slave servers (if any), type Ctrl-D to finish, and enter y to confirm the
list of NIS servers. The host names must be resolvable to IP addresses in DNS or by entries in /etc/
hosts.
The ypinit utility builds the domain subdirectory in /var/yp and makes the NIS maps that are
defined for the all target in /var/yp/Makefile. If you have configured NOPUSH=false in /var/
yp/Makefile and the names of the slave servers in /var/yp/ypservers, the command also
pushes the updated maps to the slave servers.
9. On each NIS slave server, run the following command to initialize the server:
# /usr/lib64/yp/ypinit -s nismaster
where nismaster is the host name or IP address of the NIS master server.
For more information, see the ypinit(8) manual page
Note
If you update any of the source files on the master NIS server that are used to build
the maps, use the following command on the master NIS server to remake the map
and push the changes out to the slave servers:
# make -C /var/yp
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Adding User Accounts to NIS
22.5.3 Adding User Accounts to NIS
Note
This procedure assumes that:
• NIS provides maps for passwd, group, and auto.home.
• The NIS master server uses NFS to export the users' home directories. See
Section 20.2.2, “Mounting an NFS File System”
Warning
NIS authentication is deprecated as it has security issues, including a lack of
protection of authentication data.
To create an account for an NIS user on the NIS master server:
1. If the NIS master server does not already export the base directory of the users' home directories,
perform the following steps on the NIS master server:
a. Create the base directory for user directories, for example /nethome:
# mkdir /nethome
b. Add an entry such as the following to /etc/exports:
/nethome
*(rw,sync)
You might prefer to restrict which clients can mount the file system. For example, the following entry
allows only clients in the 192.168.1.0/24 subnet to mount /nethome:
/nethome
192.168.1.0/24(rw,sync)
c. Use the following command to export the file system:
# exportfs -i -o ro,sync *:/nethome
d. If you have configured /var/yp/Makfile to make the auto.home map available to NIS clients,
create the following entry in /etc/auto.home:
*
-rw,sync
nissvr:/nethome/&
where nissvr is the host name or IP address of the NIS server.
2. Create the user account:
# useradd -b /nethome username
The command updates the /etc/passwd file and creates a home directory on the NIS server.
3. Depending on the type of authentication that you have configured:
• For Kerberos authentication, on the Kerberos server or a client system with kadmin access, use
kadmin to create a principal for the user in the Kerberos domain, for example:
# kadmin -q "addprinc [email protected]"
The command prompts you to set a password for the user, and adds the principal to the Kerberos
database.
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Enabling NIS Authentication
• For NIS authentication, use the passwd command:
# passwd username
The command updates the /etc/shadow file with the hashed password.
4. Update the NIS maps:
# make -C /var/yp
This command makes the NIS maps that are defined for the all target in /var/yp/Makefile. If you
have configured NOPUSH=false in /var/yp/Makefile and the names of the slave servers in /var/
yp/ypservers, the command also pushes the updated maps to the slave servers.
Note
A Kerberos-authenticated user can use either kpasswd or passwd to change his or
her password. An NIS-authenticated user must use the yppasswd command rather
than passwd to change his or her password.
22.5.4 Enabling NIS Authentication
To enable NIS authentication for an NIS client by using the Authentication Configuration GUI:
1. Install the yp-tools and ypbind packages:
# yum install yp-tools ypbind
2. Run the Authentication Configuration GUI:
# system-config-authentication
3. Select NIS as the user account database and enter values for:
NIS Domain
The name of the NIS domain. For example: mynisdom.
NIS Server
The domain name or IP address of the NIS server. For example, nissvr.mydom.com.
4. Select either Kerberos password or NIS password for authentication.
5. If you select Kerberos authentication, enter values for:
Realm
The name of the Kerberos realm.
KDCs
A comma-separated list of Key Distribution Center (KDC) servers that can issue
Kerberos ticket granting tickets and service tickets.
Admin Servers
A comma-separated list of Kerberos administration servers.
Alternatively, you can use DNS to configure these settings:
• Select the Use DNS to resolve hosts to realms check box to look up the name of the realm defined
as a TXT record in DNS, for example:
_kerberos.mydom.com
IN TXT "MYDOM.COM"
• Select the Use DNS to locate KDCs for realms check box to look up the KDCs and administration
servers defined as SVR records in DNS, for example:
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Enabling NIS Authentication
_kerberos._tcp.mydom.com
_kerberos._udp.mydom.com
_kpasswd._udp.mydom.com
_kerberos-adm._tcp.mydom.com
IN
IN
IN
IN
SVR
SVR
SVR
SVR
1
1
1
1
0
0
0
0
88
88
464
749
krbsvr.mydom.com
krbsvr.mydom.com
krbsvr.mydom.com
krbsvr.mydom.com
6. Click Apply to save your changes.
Warning
NIS authentication is deprecated as it has security issues, including a lack of
protection of authentication data.
Figure 22.4 shows the Authentication Configuration GUI with NIS selected as the user account database
and Kerberos selected for authentication.
Figure 22.4 Authentication Configuration of NIS with Kerberos Authentication
You can also enable and configure NIS or Kerberos authentication by using the authconfig command.
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About Kerberos Authentication
For example, to use NIS authentication, specify the --enablenis option together with the NIS domain
name and the host name or IP address of the master server, as shown in the following example:.
# authconfig --enablenis --nisdomain mynisdom \
--nisserver nissvr.mydom.com –-update
The --enablenis option configures /etc/nsswitch.conf to enable the system to use NIS for
information services. The --nisdomain and --nisserver settings are added to /etc/yp.conf.
For more information, see the authconfig(8), nsswitch.conf(5), and yp.conf(5) manual pages.
For information about using Kerberos authentication with NIS, see Section 22.6.3, “Enabling Kerberos
Authentication”.
22.5.4.1 Configuring an NIS Client to Use Automount Maps
If you have configured an automount map for auto.home in NIS, you can configure an NIS client to mount
the users' home directories when they log in.
To configure an NIS client to automount users' home directories:
1. Install the autofs package:
# yum install autofs
2. Create an /etc/auto.master file that contains the following entry:
/nethome
/etc/auto.home
3. Verify that the auto.home map is available:
# ypcat -k auto.home
*
-rw,sync
nfssvr:/nethome/&
In this example, the map is available. For details of how to make this map available, see Section 22.5.3,
“Adding User Accounts to NIS”.
4. If the auto.home map is available, edit the file /etc/auto.home to contain the following entry:
+auto.home
This entry causes the automounter to use the auto.home map.
5. Restart the autofs service, and configure the service to start following a system reboot:
# service autofs restart
# chkconfig autofs on
The autofs service creates the directory /nethome. When a user logs in, the automounter mounts
his or her home directory under /nethome.
If the owner and group for the user's files are unexpectedly listed as the anonymous user or group
(nobody or nogroup) and all_squash has not been specified as a mount option, verify that the
Domain setting in /etc/idmapd.conf on the NFS server is set to the DNS domain name. Restart the
NFS services on the NFS server if you change this file.
22.6 About Kerberos Authentication
Both LDAP and NIS authentication optionally support Kerberos authentication. In the case of IPA, Kerberos
is fully integrated. Kerberos provides a secure connection over standard ports, and it also allows offline
logins if you enable credential caching in SSSD.
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About Kerberos Authentication
Figure 22.5 illustrates how a Kerberos Key Distribution Center (KDC) authenticates a principal, which can
be a user or a host, and grants a Ticket Granting Ticket (TGT) that the principal can use to gain access to
a service.
Figure 22.5 Kerberos Authentication
The steps in the process are:
1. A principal name and key are specified to the client.
2. The client sends the principal name and a request for a TGT to the KDC.
The KDC generates a session key and a TGT that contains a copy of the session key, and uses the
Ticket Granting Service (TGS) key to encrypt the TGT. It then uses the principal's key to encrypt both
the already encrypted TGT and another copy of the session key.
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About Kerberos Authentication
3. The KDC sends the encrypted combination of the session key and the encrypted TGT to the client.
The client uses the principal's key to extract the session key and the encrypted TGT.
4. When the client want to use a service, usually to obtain access to a local or remote host system, it uses
the session key to encrypt a copy of the encrypted TGT, the client’s IP address, a time stamp, and a
service ticket request, and it sends this item to the KDC.
The KDC uses its copies of the session key and the TGS key to extract the TGT, IP address, and
time stamp, which allow it to validate the client. Provided that both the client and its service request
are valid, the KDC generates a service session key and a service ticket that contains the client’s IP
address, a time stamp, and a copy of the service session key, and it uses the service key to encrypt the
service ticket. It then uses the session key to encrypt both the service ticket and another copy of the
service session key.
The service key is usually the host principal's key for the system on which the service provider runs.
5. The KDC sends the encrypted combination of the service session key and the encrypted service ticket
to the client.
The client uses its copy of the session key to extract the encrypted service ticket and the service
session key.
6. The client sends the encrypted service ticket to the service provider together with the principal name
and a time stamp encrypted with the service session key.
The service provider uses the service key to extract the data in the service session ticket, including the
service session key.
7. The service provider enables the service for the client, which is usually to grant access to its host
system.
If the client and service provider are hosted on different systems, they can each use their own copy of
the service session key to secure network communication for the service session.
Note the following points about the authentication handshake:
• Steps 1 through 3 correspond to using the kinit command to obtain and cache a TGT.
• Steps 4 through 7 correspond to using a TGT to gain access to a Kerberos-aware service.
• Authentication relies on pre-shared keys.
• Keys are never sent in the clear over any communications channel between the client, the KDC, and the
service provider.
• At the start of the authentication process, the client and the KDC share the principal's key, and the KDC
and the service provider share the service key. Neither the principal nor the service provider know the
TGS key.
• At the end of the process, both the client and the service provider share a service session key that they
can use to secure the service session. The client does not know the service key and the service provider
does not know the principal's key.
• The client can use the TGT to request access to other service providers for the lifetime of the ticket,
which is usually one day. The session manager renews the TGT if it expires while the session is active.
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Configuring a Kerberos Server
22.6.1 Configuring a Kerberos Server
If you want to configure any client systems to use Kerberos authentication, it is recommended that you first
configure a Kerberos server. You can then configure any clients that you require.
Note
Keep any system that you configure as a Kerberos server very secure, and do not
configure it to perform any other service function.
To configure a Kerberos server that can act as a key distribution center (KDC) and a Kerberos
administration server:
1. Configure the server to use DNS and that both direct and reverse name lookups of the server's domain
name and IP address work.
For more information about configuring DNS, see Chapter 13, Name Service Configuration.
2. Configure the server to use network time synchronization mechanism such as the Network Time
Protocol (NTP) or Precision Time Protocol (PTP). Kerberos requires that the system time on Kerberos
servers and clients are synchronized as closely as possible. If the system times of the server and a
client differ by more than 300 seconds (by default), authentication fails.
For more information, see Chapter 14, Network Time Configuration.
3. Install the krb5-libs, krb5-server, and krb5-workstation packages:
# yum install krb5-libs krb5-server krb5-workstation
4. Edit /etc/krb5.conf and configure settings for the Kerberos realm, for example:
[logging]
default = FILE:/var/log/krb5libs.log
kdc = FILE:/var/log/krb5kdc.log
admin_server = FILE:/var/log/kadmind.log
[libdefaults]
default_realm = MYDOM.COM
dns_lookup_realm = false
dns_lookup_kdc = false
ticket_lifetime = 24h
renew_lifetime = 7d
forwardable = true
[realms]
MYDOM.COM = {
kdc = krbsvr.mydom.com
admin_server = krbsvr.mydom.com
}
[domain_realm]
.mydom.com = MYDOM.COM
mydom.com = MYDOM.COM
[appdefaults]
pam = {
debug = true
validate = false
}
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Configuring a Kerberos Server
In this example, the Kerberos realm is MYDOM.COM in the DNS domain mydom.com and
krbsvr.mydom.com (the local system) acts as both a KDC and an administration server. The
[appdefaults] section configures options for the pam_krb5.so module.
For more information, see the krb5.conf(5) and pam_krb5(5) manual pages.
5. Edit /var/kerberos/krb5kdc/kdc.conf and configure settings for the key distribution center, for
example:
kdcdefaults]
kdc_ports = 88
kdc_tcp_ports = 88
[realms]
MYDOM.COM = {
#master_key_type = aes256-cts
master_key_type = des-hmac-sha1
default_principal_flags = +preauth
acl_file = /var/kerberos/krb5kdc/kadm5.acl
dict_file = /usr/share/dict/words
admin_keytab = /etc/kadm5.keytab
supported_enctypes = aes256-cts:normal aes128-cts:normal des3-hmac-sha1:normal \
arcfour-hmac:normal des-hmac-sha1:normal des-cbc-md5:normal des-cbc-crc:normal
}
For more information, see the kdc.conf(5) manual page.
6. Create the Kerberos database and store the database password in a stash file:
# /usr/sbin/kdb5_util create -s
7. Edit /var/kerberos/krb5kdc/kadm5.acl and define the principals who have administrative
access to the Kerberos database, for example:
[email protected]
*
In this example, any principal who has an instance of admin, such as [email protected],
has full administrative control of the Kerberos database for the MYDOM.COM domain. Ordinary users
in the database usually have an empty instance, for example [email protected] These users have no
administrative control other than being able to change their password, which is stored in the database.
8. Create a principal for each user who should have the admin instance, for example:
# kadmin.local -q "addprinc alice/admin"
9. Cache the keys that kadmind uses to decrypt administration Kerberos tickets in /etc/
kadm5.keytab:
# kadmin.local -q "ktadd -k /etc/kadm5.keytab kadmin/admin"
# kadmin.local -q "ktadd -k /etc/kadm5.keytab kadmin/changepw"
10. Start the KDC and administration services and configure them to start following system reboots:
#
#
#
#
service krb5kdc start
service kadmin start
chkconfig krb5kdc on
chkconfig kadmin on
11. Add principals for users and the Kerberos server and cache the key for the server's host principal in /
etc/kadm5.keytab by using either kadmin.local or kadmin, for example:
# kadmin.local -q "addprinc bob"
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Configuring a Kerberos Client
# kadmin.local -q "addprinc -randkey host/krbsvr.mydom.com"
# kadmin.local -q "ktadd -k /etc/kadm5.keytab host/krbsvr.mydom.com"
12. Allow incoming TCP connections to ports 88, 464, and 749 and UDP datagrams on UDP port 88, 464,
and 749:
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m state --state NEW -m tcp -–dport 88 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m state --state NEW -m tcp -–dport 464 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m state --state NEW -m tcp -–dport 749 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m udp -–dport 88 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m udp -–dport 464 -j ACCEPT
# iptables -I INPUT -s subnet_addr/prefix_length -p
-m udp -–dport 749 -j ACCEPT
# service iptables save
tcp \
tcp \
tcp \
udp \
udp \
udp \
where subnet_addr/prefix_length specifies the network address, for example
192.168.1.0/24.
krb5kdc services requests on TCP port 88 and UDP port 88, and kadmind services requests on TCP
ports 464 and 749 and UDP ports 464 and 749.
In addition, you might need to allow TCP and UDP access on different ports for other applications.
For more information, see the kadmin(1) manual page.
22.6.2 Configuring a Kerberos Client
Setting up a Kerberos client on a system allows it to use Kerberos to authenticate users who are defined
in NIS or LDAP, and to provide secure remote access by using commands such as ssh with GSS-API
enabled or the Kerberos implementation of telnet.
To set up a system as a Kerberos client:
1. Configure the client system to use DNS and that both direct and reverse name lookups of the domain
name and IP address for both the client and the Kerberos server work.
For more information about configuring DNS, see Chapter 13, Name Service Configuration.
2. Configure the system to use a network time synchronization protocol such as the Network Time
Protocol (NTP). Kerberos requires that the system time on Kerberos servers and clients are
synchronized as closely as possible. If the system times of the server and a client differ by more than
300 seconds (by default), authentication fails.
To configure the server as an NTP client:
a. Install the ntp package:
# yum install ntp
b. Edit /etc/ntp.conf and configure the settings as required. See the ntp.conf(5) manual page
and http://www.ntp.org.
c. Start the ntpd service and configure it to start following system reboots.
# service ntpd start
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Enabling Kerberos Authentication
# chkconfig ntpd on
3. Install the krb5-libs and krb5-workstation packages:
# yum install krb5-libs krb5-workstation
4. Copy the /etc/krb5.conf file to the system from the Kerberos server.
5. Use the Authentication Configuration GUI or authconfig to set up the system to use Kerberos with
either NIS or LDAP, for example:
# authconfig --enablenis --enablekrb5 --krb5realm=MYDOM.COM \
--krb5adminserver=krbsvr.mydom.com --krb5kdc=krbsvr.mydom.com \
--update
See Section 22.6.3, “Enabling Kerberos Authentication”.
6. On the Kerberos KDC, use either kadmin or kadmin.local to add a host principal for the client, for
example:
# kadmin.local -q "addprinc -randkey host/client.mydom.com"
7. On the client system, use kadmin to cache the key for its host principal in /etc/kadm5.keytab, for
example:
# kadmin -q "ktadd -k /etc/kadm5.keytab host/client.mydom.com"
8. To use ssh and related OpenSSH commands to connect from Kerberos client system to another
Kerberos client system:
a. On the remote Kerberos client system, verify that GSSAPIAuthentication is enabled in /etc/
ssh/sshd_config:
GSSAPIAuthentication yes
b. On the local Kerberos client system, enable GSSAPIAuthentication and
GSSAPIDelegateCredentials in the user's .ssh/config file:
GSSAPIAuthentication yes
GSSAPIDelegateCredentials yes
Alternatively, the user can specify the -K option to ssh.
c. Test that the principal can obtain a ticket and connect to the remote system, for example:
$ kinit [email protected]
$ ssh [email protected]
To allow use of the Kerberos versions of rlogin, rsh, and telnet, which are provided in the krb5appl-clients package, you must enable the corresponding services on the remote client.
For more information, see the kadmin(1) manual page.
22.6.3 Enabling Kerberos Authentication
To be able to use Kerberos authentication with an LDAP or NIS client, use yum to install the krb5-libs
and krb5-workstation packages.
If you use the Authentication Configuration GUI (system-config-authentication) and select LDAP
or NIS as the user account database, select Kerberos password as the authentication method and enter
values for:
297
Enabling Kerberos Authentication
Realm
The name of the Kerberos realm.
KDCs
A comma-separated list of Key Distribution Center (KDC) servers that can issue
Kerberos ticket granting tickets and service tickets.
Admin Servers
A comma-separated list of Kerberos administration servers.
Alternatively, you can use DNS to configure these settings:
• Select the Use DNS to resolve hosts to realms check box to look up the name of the realm defined as
a TXT record in DNS, for example:
_kerberos.mydom.com
IN TXT "MYDOM.COM"
• Select the Use DNS to locate KDCs for realms check box to look up the KDCs and administration
servers defined as SVR records in DNS, for example:
_kerberos._tcp.mydom.com
_kerberos._udp.mydom.com
_kpasswd._udp.mydom.com
_kerberos-adm._tcp.mydom.com
IN
IN
IN
IN
SVR
SVR
SVR
SVR
1
1
1
1
0
0
0
0
88
88
464
749
krbsvr.mydom.com
krbsvr.mydom.com
krbsvr.mydom.com
krbsvr.mydom.com
Figure 22.6 shows the Authentication Configuration GUI with LDAP selected as the user account database
and Kerberos selected for authentication.
298
Enabling Kerberos Authentication
Figure 22.6 Authentication Configuration of LDAP with Kerberos Authentication
Alternatively, you can use the authconfig command to configure Kerberos authentication with LDAP, for
example:
# authconfig --enableldap \
--ldapbasedn="dc=mydom,dc=com" --ldapserver=ldap://ldap.mydom.com:389 \
[--enableldaptls --ldaploadcacert=https://ca-server.mydom.com/CAcert.pem] \
--enablekrb5 \
--krb5realm=MYDOM.COM | --enablekrb5realmdns \
--krb5kdc=krbsvr.mydom.com --krb5adminserver=krbsvr.mydom.com | --enablekrb5kdcdns \
--update
299
About Pluggable Authentication Modules
or with NIS:
# authconfig --enablenis \
--enablekrb5 \
--krb5realm=MYDOM.COM | --enablekrb5realmdns \
--krb5kdc=krbsvr.mydom.com --krb5adminserver=krbsvr.mydom.com | --enablekrb5kdcdns \
--update
The --enablekrb5 option enables Kerberos authentication by modifying the PAM configuration files in /
etc/pam.d to use the pam_krb5.so module. The --enableldap and --enablenis options configure
/etc/nsswitch.conf to enable the system to use LDAP or NIS for information services.
For more information, see the authconfig(8), nsswitch.conf(5), and pam_krb5(5) manual pages.
22.7 About Pluggable Authentication Modules
The Pluggable Authentication Modules (PAM) feature is an authentication mechanism that allows you to
configure how applications use authentication to verify the identity of a user. The PAM configuration files,
which are located in the /etc/pam.d directory, describe the authentication procedure for an application.
The name of each configuration file is the same as, or is similar to, the name of the application for which
the module provides authentication. For example, the configuration files for passwd and sudo are named
passwd and sudo.
22.7.1 Configuring Pluggable Authentication Modules
Each PAM configuration file contains a list (stack) of calls to authentication modules. For example, the
following is the content of the login configuration file:
#%PAM-1.0
auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
auth
include
system-auth
account
required
pam_nologin.so
account
include
system-auth
password
include
system-auth
# pam_selinux.so close should be the first session rule
session
required
pam_selinux.so close
session
required
pam_loginuid.so
session
optional
pam_console.so
# pam_selinux.so open should only be followed by sessions to be executed in the user context
session
required
pam_selinux.so open
session
required
pam_namespace.so
session
optional
pam_keyinit.so force revoke
session
include
system-auth
-session
optional
pam_ck_connector.so
Comments in the file start with a # character. The remaining lines each define an operation type, a control
flag, the name of a module such as pam_rootok.so or the name of an included configuration file such as
system-auth, and any arguments to the module. PAM provides authentication modules as 32 and 64-bit
shared libraries in /lib/security and /lib64/security respectively.
For a particular operation type, PAM reads the stack from top to bottom and calls the modules listed in the
configuration file. Each module generates a success or failure result when called.
The following operation types are defined for use:
auth
The module tests whether a user is authenticated or authorized to use a service or
application. For example, the module might request and verify a password. Such modules can
also set credentials, such as a group membership or a Kerberos ticket.
300
About the System Security Services Daemon
account
The module tests whether an authenticated user is allowed access to a service or application.
For example, the module might check if a user account has expired or if a user is allowed to
use a service at a given time.
password
The module handles updates to an authentication token.
session
The module configures and manages user sessions, performing tasks such as mounting or
unmounting a user's home directory.
If the operation type is preceded with a dash (-), PAM does not add an create a system log entry if the
module is missing.
With the exception of include, the control flags tell PAM what to do with the result of running a module.
The following control flags are defined for use:
optional
The module is required for authentication if it is the only module listed for a service.
required
The module must succeed for access to be granted. PAM continues to execute the
remaining modules in the stack whether the module succeeds or fails. PAM does not
immediately inform the user of the failure.
requisite
The module must succeed for access to be granted. If the module succeeds, PAM
continues to execute the remaining modules in the stack. However, if the module fails,
PAM notifies the user immediately and does not continue to execute the remaining
modules in the stack.
sufficient
If the module succeeds, PAM does not process any remaining modules of the same
operation type. If the module fails, PAM processes the remaining modules of the same
operation type to determine overall success or failure.
The control flag field can also define one or more rules that specify the action that PAM should take
depending on the value that a module returns. Each rule takes the form value=action, and the rules are
enclosed in square brackets, for example:
[user_unknown=ignore success=ok ignore=ignore default=bad]
If the result returned by a module matches a value, PAM uses the corresponding action, or, if there is no
match, it uses the default action.
The include flag specifies that PAM must also consult the PAM configuration file specified as the
argument.
Most authentication modules and PAM configuration files have their own manual pages. In addition, the
/usr/share/doc/pam-version directory contains the PAM System Administrator’s Guide (html/
Linux-PAM_SAG.html or Linux-PAM_SAG.txt) and a copy of the PAM standard (rfc86.0.txt).
For more information, see the pam(8) manual page. In addition, each PAM module has its own manual
page, for example pam_unix(8).
22.8 About the System Security Services Daemon
The System Security Services Daemon (SSSD) feature provides access on a client system to remote
identity and authentication providers. The SSSD acts as an intermediary between local clients and any
back-end provider that you configure.
The benefits of configuring SSSD include:
• Reduced system load
301
Configuring an SSSD Server
Clients do not have to contact the identification or authentication servers directly.
• Offline authentication
You can configure SSSD to maintain a cache of user identities and credentials.
• Single sign-on access
If you configure SSSD to store network credentials, users need only authenticate once per session with
the local system to access network resources.
For more information, see the authconfig(8), pam_sss(8), sssd(8), and sssd.conf(5) manual
pages and https://fedorahosted.org/sssd/.
22.8.1 Configuring an SSSD Server
To configure an SSSD server:
1. Install the sssd and sssd-client packages:
# yum install sssd sssd-client
2. Edit the /etc/sssd/sssd.conf configuration file and configure the sections to support the required
services, for example:
[sssd]
config_file_version = 2
domains = LDAP
services = nss, pam
[domain/LDAP]
id_provider = ldap
ldap_uri = ldap://ldap.mydom.com
ldap_search_base = dc=mydom,dc=com
auth_provider = krb5
krb5_server = krbsvr.mydom.com
krb5_realm = MYDOM.COM
cache_credentials = true
min_id = 5000
max_id = 25000
enumerate = false
[nss]
filter_groups = root
filter_users = root
reconnection_retries = 3
entry_cache_timeout = 300
[pam]
reconnection_retries = 3
offline_credentials_expiration = 2
offline_failed_login_attempts = 3
offline_failed_login_delay = 5
The [sssd] section contains configuration settings for SSSD monitor options, domains, and services.
The SSSD monitor service manages the services that SSSD provides.
The services entry defines the supported services, which should include nss for the Name Service
Switch and pam for Pluggable Authentication Modules.
302
Configuring an SSSD Server
The domains entry specifies the name of the sections that define authentication domains.
The [domain/LDAP] section defines a domain for an LDAP identity provider that uses Kerberos
authentication. Each domain defines where user information is stored, the authentication method, and
any configuration options. SSSD can work with LDAP identity providers such as OpenLDAP, Red Hat
Directory Server, IPA, and Microsoft Active Directory, and it can use either native LDAP or Kerberos
authentication.
The id_provider entry specifies the type of provider (in this example, LDAP). ldap_uri specifies
a comma-separated list of the Universal Resource Identifiers (URIs) of the LDAP servers, in order of
preference, to which SSSD can connect. ldap_search_base specifies the base distinguished name
(dn) that SSSD should use when performing LDAP user operations on a relative distinguished name
(RDN) such as a common name (cn).
The auth_provider entry specifies the authentication provider (in this example, Kerberos).
krb5_server specifies a comma-separated list of Kerberos servers, in order of preference, to which
SSSD can connect. krb5_realm specifies the Kerberos realm. cache_credentials specifies
if SSSD caches user credentials such as tickets, session keys, and other identifying information to
support offline authentication and single sign-on.
Note
To allow SSSD to use Kerberos authentication with an LDAP server, you must
configure the LDAP server to use both Simple Authentication and Security
Layer (SASL) and the Generic Security Services API (GSSAPI). For more
information about configuring SASL and GSSAPI for OpenLDAP, see http://
www.openldap.org/doc/admin24/sasl.html.
The min_id and max_id entries specify upper and lower limits on the values of user and group IDs.
enumerate specifies whether SSSD caches the complete list of users and groups that are available
on the provider. The recommended setting is False unless a domain contains relatively few users or
groups.
The [nss] section configures the Name Service Switch (NSS) module that integrates the SSS
database with NSS. The filter_users and filter_groups entries prevent NSS retrieving
information about the specified users and groups being retrieved from SSS. reconnection_retries
specifies the number of times that SSSD should attempt to reconnect if a data provider crashes.
enum_cache_timeout specifies the number of seconds for which SSSD caches user information
requests.
The [pam] section configures the PAM module that integrates SSS with PAM. The
offline_credentials_expiration entry specifies the number of days for which to allow
cached logins if the authentication provider is offline. offline_failed_login_attempts
specifies how many failed login attempts are allowed if the authentication provider
is offline. offline_failed_login_delay specifies how many minutes after
offline_failed_login_attempts failed login attempts that a new login attempt is permitted.
3. Change the mode of /etc/sssd/sssd.conf to 0600:
# chmod 0600 /etc/sssd/sssd.conf
4. Enable the SSSD service:
# authconfig --update --enablesssd –-enablesssdauth
303
About Winbind Authentication
Note
If you edit /etc/sssd/sssd.conf, use this command to update the service.
The –-enablesssd option updates /etc/nsswitch.conf to support SSS.
The –-enablesssdauth option updates /etc/pam.d/system-auth to include the required
pam_sss.so entries to support SSSD.
22.9 About Winbind Authentication
Winbind is a client-side service that resolves user and group information on a Windows server, and allows
Oracle Linux to understand Windows users and groups. To be able to configure Winbind authentication,
use yum to install the samba-winbind package. This package includes the winbindd daemon that
implements the winbind service.
22.9.1 Enabling Winbind Authentication
If you use the Authentication Configuration GUI and select Winbind as the user account database, you
are prompted for the information that is required to connect to a Microsoft workgroup, Active Directory, or
Windows NT domain controller. Enter the name of the Winbind domain and select the security model for
the Samba server:
ads
In the Activity Directory Server (ADS) security model, Samba acts as a domain member in
an ADS realm, and clients use Kerberos tickets for Active Directory authentication. You must
configure Kerberos and join the server to the domain, which creates a machine account for your
server on the domain controller.
domain
In the domain security model, the local Samba server has a machine account (a domain security
trust account) and Samba authenticates user names and passwords with a domain controller in
a domain that implements Windows NT4 security.
Warning
If the local machine acts as a Primary or Backup Domain Controller, do
not use the domain security model. Use the user security model instead.
server
In the server security model, the local Samba server authenticates user names and passwords
with another server, such as a Windows NT server.
Warning
The server security model is deprecated as it has numerous security
issues.
user
In the user security model, a client must log in with a valid user name and password. This model
supports encrypted passwords. If the server successfully validates the client's user name and
password, the client can mount multiple shares without being required to specify a password.
Depending on the security model that you choose, you might also need to specify the following information:
• The name of the ADS realm that the Samba server is to join (ADS security model only).
• The names of the domain controllers. If there are several domain controllers, separate the names with
spaces.
304
Enabling Winbind Authentication
• The login template shell to use for the Windows NT user account (ADS and domain security models
only).
• Whether to allow user authentication using information that has been cached by the System Security
Services Daemon (SSSD) if the domain controllers are offline.
Your selection updates the security directive in the [global] section of the /etc/samba/smb.conf
configuration file.
If you have initialized Kerberos, you can click Join Domain to create a machine account on the Active
Directory server and grant permission for the Samba domain member server to join the domain.
You can also use the authconfig command to configure Winbind authentication. To use the userlevel security models, specify the name of the domain or workgroup and the host names of the domain
controllers. for example:
# authconfig --enablewinbind --enablewinbindauth --smbsecurity user \
[--enablewinbindoffline] --smbservers="ad1.mydomain.com ad2.mydomain.com" \
--smbworkgroup=MYDOMAIN --update
To allow user authentication using information that has been cached by the System Security Services
Daemon (SSSD) if the domain controllers are offline, specify the --enablewinbindoffline option.
For the domain security model, additionally specify the template shell, for example:
# authconfig --enablewinbind --enablewinbindauth --smbsecurity domain \
[--enablewinbindoffline] --smbservers="ad1.mydomain.com ad2.mydomain.com" \
--smbworkgroup=MYDOMAIN --update --winbindtemplateshell=/bin/bash --update
For the ADS security model, additionally specify the ADS realm and template shell, for example:
# authconfig --enablewinbind --enablewinbindauth --smbsecurity ads \
[--enablewinbindoffline] --smbservers="ad1.mydomain.com ad2.mydomain.com" \
--smbworkgroup=MYDOMAIN --update --smbrealm MYDOMAIN.COM \
--winbindtemplateshell=/bin/bash --update
For more information, see the authconfig(8) manual page.
305
306
Chapter 23 Local Account Configuration
Table of Contents
23.1 About User and Group Configuration ....................................................................................... 307
23.2 Changing Default Settings for User Accounts ........................................................................... 308
23.3 Creating User Accounts .......................................................................................................... 308
23.3.1 About umask and the setgid and Restricted Deletion Bits ............................................... 309
23.4 Locking an Account ................................................................................................................. 309
23.5 Modifying or Deleting User Accounts ....................................................................................... 309
23.6 Creating Groups ..................................................................................................................... 310
23.7 Modifying or Deleting Groups .................................................................................................. 310
23.8 Configuring Password Ageing .................................................................................................. 310
23.9 Granting sudo Access to Users ............................................................................................... 311
This chapter describes how to configure and manage local user and group accounts.
23.1 About User and Group Configuration
You can use the User Manager GUI (system-config-users) to add or delete users and groups and to
modify settings such as passwords, home directories, login shells, and group membership. Alternatively,
you can use commands such as useradd and groupadd.
Figure 23.1 shows the User Manager GUI with the Users tab selected.
Figure 23.1 User Manager
307
Changing Default Settings for User Accounts
In an enterprise environment that might have hundreds of servers and thousands of users, user and group
account information is more likely to be held in a central repository rather than in files on individual servers.
You can configure user and group information on a central server and retrieve this information by using
services such as Lightweight Directory Access Protocol (LDAP) or Network Information Service (NIS). You
can also create users’ home directories on a central server and automatically mount, or access, these
remote file systems when a user logs in to a system.
23.2 Changing Default Settings for User Accounts
To display the default settings for an account use the following command:
# useradd -D
GROUP=100
HOME=/home
INACTIVE=-1
EXPIRE=
SHELL=/bin/bash
SKEL=/etc/skel
CREATE_MAIL_SPOOL=yes
INACTIVE specifies after how many days the system locks an account if a user's password expires. If set
to 0, the system locks the account immediately. If set to -1, the system does not lock the account.
SKEL defines a template directory, whose contents are copied to a newly created user’s home directory.
The contents of this directory should match the default shell defined by SHELL.
You can specify options to useradd -D to change the default settings for user accounts. For example, to
change the defaults for INACTIVE, HOME and SHELL:
# useradd -D -f 3 -b /home2 -s /bin/sh
Note
If you change the default login shell, you would usually also create a new SKEL
template directory with contents that are appropriate to the new shell.
If you specify /sbin/nologin for a user's SHELL, that user cannot log into the
system directly but processes can run with that user's ID. This setting is typically
used for services that run as users other than root.
The default settings are stored in the /etc/default/useradd file.
For more information, see Section 23.8, “Configuring Password Ageing” and the useradd(8) manual
page.
23.3 Creating User Accounts
To create a user account by using the useradd command:
1. Enter the following command to create a user account:
# useradd [options] username
You can specify options to change the account's settings from the default ones.
By default, if you specify a user name argument but do not specify any options, useradd creates a
locked user account using the next available UID and assigns a user private group (UPG) rather than
the value defined for GROUP as the user's group.
308
About umask and the setgid and Restricted Deletion Bits
2. Assign a password to the account to unlock it:
# passwd username
The command prompts you to enter a password for the account.
If you want to change the password non-interactively (for example, from a script), use the chpasswd
command instead:
echo "username:password" | chpasswd
Alternatively, you can use the newusers command to create a number of user accounts at the same time.
For more information, see the chpasswd(8), newusers(8), passwd(1), and useradd(8) manual
pages.
23.3.1 About umask and the setgid and Restricted Deletion Bits
Users whose primary group is not a UPG have a umask of 0022 set by /etc/profile or /etc/bashrc,
which prevents other users, including other members of the primary group, from modifying any file that the
user owns.
A user whose primary group is a UPG has a umask of 0002. It is assumed that no other user has the same
group.
To grant users in the same group write access to files within the same directory, change the group
ownership on the directory to the group, and set the setgid bit on the directory:
# chgrp groupname directory
# chmod g+s directory
Files created in such a directory have their group set to that of the directory rather than the primary group
of the user who creates the file.
The restricted deletion bit prevents unprivileged users from removing or renaming a file in the directory
unless they own either the file or the directory.
To set the restricted deletion bit on a directory:
# chmod a+t directory
For more information, see the chmod(1) manual page.
23.4 Locking an Account
To lock a user's account, enter:
# passwd -l username
To unlock the account:
# passwd -u username
For more information, see the passwd(1) manual page.
23.5 Modifying or Deleting User Accounts
To modify a user account, use the usermod command:
309
Creating Groups
# usermod [options] username
For example, to add a user to a supplementary group (other than his or her login group):
# usermod -aG groupname username
You can use the groups command to display the groups to which a user belongs, for example:
# groups root
root : root bin daemon sys adm disk wheel
To delete a user's account, use the userdel command:
# userdel username
For more information, see the groups(1), userdel(8) and usermod(8) manual pages.
23.6 Creating Groups
To create a group by using the groupadd command:
# groupadd [options] groupname
Typically, you might want to use the -g option to specify the group ID (GID). For example:
# groupadd -g 1000 devgrp
For more information, see the groupadd(8) manual page.
23.7 Modifying or Deleting Groups
To modify a group, use the groupmod command:
# groupmod [options] username
To delete a user's account, use the groupdel command:
# groupdel username
For more information, see the groupdel(8) and groupmod(8) manual pages.
23.8 Configuring Password Ageing
To specify how users' passwords are aged, edit the following settings in the /etc/login.defs file:
Setting
Description
PASS_MAX_DAYS
Maximum number of days for which a password can be used before it must be
changed. The default value is 99,999 days.
PASS_MIN_DAYS
Minimum number of days that is allowed between password changes. The
default value is 0 days.
PASS_WARN_AGE
Number of days warning that is given before a password expires. The default
value is 7 days.
For more information, see the login.defs(5) manual page.
To change how long a user's account can be inactive before it is locked, use the usermod command. For
example, to set the inactivity period to 30 days:
310
Granting sudo Access to Users
# usermod -f 30 username
To change the default inactivity period for new user accounts, use the useradd command:
# useradd -D -f 30
A value of -1 specifies that user accounts are not locked due to inactivity.
For more information, see the useradd(8) and usermod(8) manual pages.
23.9 Granting sudo Access to Users
By default, an Oracle Linux system is configured so that you cannot log in directly as root. You must log
in as a named user before using either su or sudo to perform tasks as root. This configuration allows
system accounting to trace the original login name of any user who performs a privileged administrative
action. If you want to grant certain users authority to be able to perform specific administrative tasks via
sudo, use the visudo command to modify the /etc/sudoers file.
For example, the following entry grants the user erin the same privileges as root when using sudo, but
defines a limited set of privileges to frank so that he can run commands such as chkconfig, service,
rpm, and yum:
erin
frank
ALL=(ALL)
ALL
ALL= SERVICES, SOFTWARE
For more information, see the su(1), sudo(8), sudoers(5), and visudo(8) manual pages.
311
312
Chapter 24 System Security Administration
Table of Contents
24.1 About System Security ............................................................................................................ 313
24.2 Configuring and Using SELinux ............................................................................................... 314
24.2.1 About SELinux Administration ....................................................................................... 315
24.2.2 About SELinux Modes .................................................................................................. 317
24.2.3 Setting SELinux Modes ................................................................................................ 317
24.2.4 About SELinux Policies ................................................................................................ 317
24.2.5 About SELinux Context ................................................................................................ 319
24.2.6 About SELinux Users ................................................................................................... 321
24.2.7 Troubleshooting Access-Denial Messages ..................................................................... 322
24.3 About Packet-filtering Firewalls ................................................................................................ 323
24.3.1 Controlling the Firewall Service ..................................................................................... 325
24.3.2 Listing Firewall Rules ................................................................................................... 325
24.3.3 Inserting and Replacing Rules in a Chain ...................................................................... 326
24.3.4 Deleting Rules in a Chain ............................................................................................. 327
24.3.5 Saving Rules ................................................................................................................ 327
24.4 About TCP Wrappers .............................................................................................................. 327
24.5 About chroot Jails ................................................................................................................... 329
24.5.1 Running DNS and FTP Services in a Chroot Jail ........................................................... 329
24.5.2 Creating a Chroot Jail .................................................................................................. 329
24.5.3 Using a Chroot Jail ...................................................................................................... 330
24.6 About Auditing ........................................................................................................................ 330
24.7 About System Logging ............................................................................................................ 331
24.7.1 Configuring Logwatch ................................................................................................... 334
24.8 About Process Accounting ....................................................................................................... 335
24.9 Security Guidelines ................................................................................................................. 335
24.9.1 Minimizing the Software Footprint ................................................................................. 335
24.9.2 Configuring System Logging ......................................................................................... 337
24.9.3 Disabling Core Dumps .................................................................................................. 337
24.9.4 Minimizing Active Services ............................................................................................ 337
24.9.5 Locking Down Network Services ................................................................................... 340
24.9.6 Configuring a Packet-filtering Firewall ............................................................................ 341
24.9.7 Configuring TCP Wrappers ........................................................................................... 341
24.9.8 Configuring Kernel Parameters ..................................................................................... 341
24.9.9 Restricting Access to SSH Connections ........................................................................ 342
24.9.10 Configuring File System Mounts, File Permissions, and File Ownerships ........................ 342
24.9.11 Checking User Accounts and Privileges ....................................................................... 344
This chapter describes the subsystems that you can use to administer system security, including SELinux,
the Netfilter firewall, TCP Wrappers, chroot jails, auditing, system logging, and process accounting.
24.1 About System Security
Oracle Linux provides a complete security stack, from network firewall control to access control security
policies, and is designed to be secure by default.
Traditional Linux security is based on a Discretionary Access Control (DAC) policy, which provides minimal
protection from broken software or from malware that is running as a normal user or as root. The SELinux
enhancement to the Linux kernel implements the Mandatory Access Control (MAC) policy, which allows
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you to define a security policy that provides granular permissions for all users, programs, processes,
files, and devices. The kernel's access control decisions are based on all the security relevant information
available, and not solely on the authenticated user identity. By default, SELinux is enabled when you install
an Oracle Linux system.
Oracle Linux has evolved into a secure enterprise-class operating system that can provide the
performance, data integrity, and application uptime necessary for business-critical production
environments.
Thousands of production systems at Oracle run Oracle Linux and numerous internal developers use it
as their development platform. Oracle Linux is also at the heart of several Oracle engineered systems,
including the Oracle Exadata Database Machine, Oracle Exalytics In-Memory Machine, Oracle Exalogic
Elastic Cloud, and Oracle Database Appliance.
Oracle On Demand services, which deliver software as a service (SaaS) at a customer's site, via an Oracle
data center, or at a partner site, use Oracle Linux at the foundation of their solution architectures. Backed
by Oracle support, these mission-critical systems and deployments depend fundamentally on the built-in
security and reliability features of the Oracle Linux operating system.
Released under an open-source license, Oracle Linux includes the Unbreakable Enterprise Kernel that
provides the latest Linux innovations while offering tested performance and stability. Oracle has been
a key participant in the Linux community, contributing code enhancements such as Oracle Cluster File
System and the Btrfs file system. From a security perspective, having roots in open source is a significant
advantage. The Linux community, which includes many experienced developers and security experts,
reviews posted Linux code extensively prior to its testing and release. The open-source Linux community
has supplied many security improvements over time, including access control lists (ACLs), cryptographic
libraries, and trusted utilities.
24.2 Configuring and Using SELinux
Traditional Linux security is based on a Discretionary Access Control (DAC) policy, which provides minimal
protection from broken software or from malware that is running as a normal user or as root. Access
to files and devices is based solely on user identity and ownership. Malware or broken software can do
anything with files and resources that the user that started the process can do. If the user is root or the
application is setuid or setgid to root, the process can have root-access control over the entire file
system.
The National Security Agency created Security Enhanced Linux (SELinux) to provide a finer-grained
level of control over files, processes, users and applications in the Linux operating system. The SELinux
enhancement to the Linux kernel implements the Mandatory Access Control (MAC) policy, which allows
you to define a security policy that provides granular permissions for all users, programs, processes,
files, and devices. The kernel's access control decisions are based on all the security relevant information
available, and not solely on the authenticated user identity.
When security-relevant access occurs, such as when a process attempts to open a file, SELinux intercepts
the operation in the kernel. If a MAC policy rule allows the operation, it continues; otherwise, SELinux
blocks the operation and returns an error to the process. The kernel checks and enforces DAC policy rules
before MAC rules, so it does not check SELinux policy rules if DAC rules have already denied access to a
resource.
The following table describes the SELinux packages that are installed by default with Oracle Linux:
Package
Description
policycoreutils
Provides utilities such as load_policy, restorecon, secon, setfiles,
semodule, sestatus, and setsebool for operating and managing
SELinux.
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Package
Description
libselinux
Provides the API that SELinux applications use to get and set process and
file security contexts, and to obtain security policy decisions.
selinux-policy
Provides the SELinux Reference Policy, which is used as the basis for other
policies, such as the SELinux targeted policy.
selinux-policytargeted
Provides support for the SELinux targeted policy, where objects outside the
targeted domains run under DAC.
libselinux-python
Contains Python bindings for developing SELinux applications.
libselinux-utils
Provides the avcstat, getenforce, getsebool, matchpathcon,
selinuxconlist, selinuxdefcon, selinuxenabled, setenforce,
and togglesebool utilities.
The following table describes a selection of useful SELinux packages that are not installed by default:
Package
Description
mcstrans
Translates SELinux levels, such as s0-s0:c0.c1023, to an easier-to-read
form, such as SystemLow-SystemHigh.
policycoreutils-gui
Provides a GUI (system-config-selinux) that you can use to manage
SELinux. For example, you can use the GUI to set the system default
enforcing mode and policy type.
policycoreutilspython
Provides additional Python utilities for operating SELinux, such as
audit2allow, audit2why, chcat, and semanage.
selinux-policy-mls
Provides support for the strict Multilevel Security (MLS) policy as an
alternative to the SELinux targeted policy.
setroubleshoot
Provides the GUI that allows you to view setroubleshoot-server
messages using the sealert command.
setroubleshootserver
Translates access-denial messages from SELinux into detailed descriptions
that you can view on the command line using the sealert command.
setools-console
Provides the Tresys Technology SETools distribution of tools and libraries,
which you can use to analyze and query policies, monitor and report audit
logs, and manage file context.
Use yum or another suitable package manager to install the SELinux packages that you require on your
system.
For more information about SELinux, refer to the SELinux Project Wiki, the selinux(8) manual page,
and the manual pages for the SELinux commands.
24.2.1 About SELinux Administration
The following table describes the utilities that you can use to administer SELinux, and the packages that
contain each utility.
Utility
Package
Description
audit2allow
policycoreutilspython
Generates SELinux policy allow_audit rules from
logs of denied operations.
audit2why
policycoreutilspython
Generates SELinux policy don’t_audit rules from
logs of denied operations.
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About SELinux Administration
Utility
Package
Description
avcstat
libselinux-utils
Displays statistics for the SELinux Access Vector
Cache (AVC).
chcat
policycoreutilspython
Changes or removes the security category for a file
or user.
findcon
setools-console
Searches for file context.
fixfiles
policycoreutils
Fixes the security context for file systems.
getenforce
libselinux-utils
Reports the current SELinux mode.
getsebool
libselinux-utils
Reports SELinux boolean values.
indexcon
setools-console
Indexes file context.
load_policy
policycoreutils
Loads a new SELinux policy into the kernel.
matchpathcon
libselinux-utils
Queries the system policy and displays the default
security context that is associated with the file path.
replcon
setools-console
Replaces file context.
restorecon
policycoreutils
Resets the security context on one or more files.
restorecond
policycoreutils
Daemon that watches for file creation and sets the
default file context.
sandbox
policycoreutilspython
Runs a command in an SELinux sandbox.
sealert
setroubleshootserver,
setroubleshoot
Acts as the user interface to the setroubleshoot
system, which diagnoses and explains SELinux
AVC denials and provides recommendations on how
to prevent such denials.
seaudit-report
setools-console
Reports from the SELinux audit log.
sechecker
setools-console
Checks SELinux policies.
secon
policycoreutils
Displays the SELinux context from a file, program,
or user input.
sediff
setools-console
Compares SELinux polices.
seinfo
setools-console
Queries SELinux policies.
selinuxconlist
libselinux-utils
Displays all SELinux contexts that are reachable by
a user.
selinuxdefcon
libselinux-utils
Displays the default SELinux context for a user.
selinuxenabled
libselinux-utils
Indicates whether SELinux is enabled.
semanage
policycoreutilspython
Manages SELinux policies.
semodule
policycoreutils
Manages SELinux policy modules.
semodule_deps
policycoreutils
Displays the dependencies between SELinux policy
packages.
semodule_expand
policycoreutils
Expands a SELinux policy module package.
semodule_link
policycoreutils
Links SELinux policy module packages together.
semodule_package
policycoreutils
Creates a SELinux policy module package.
sesearch
setools-console
Queries SELinux policies.
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About SELinux Modes
Utility
Package
Description
sestatus
policycoreutils
Displays the SELinux mode and the SELinux policy
that are in use.
setenforce
libselinux-utils
Modifies the SELinux mode.
setsebool
policycoreutils
Sets SELinux boolean values.
setfiles
policycoreutils
Sets the security context for one or more files.
system-configselinux
policycoreutils-gui Provides a GUI that you can use to manage
SELinux.
togglesebool
libselinux-utils
Flips the current value of an SELinux boolean.
24.2.2 About SELinux Modes
SELinux runs in one of three modes.
Disabled
The kernel uses only DAC rules for access control. SELinux does not enforce any security
policy because no policy is loaded into the kernel.
Enforcing
The kernel denies access to users and programs unless permitted by SELinux security
policy rules. All denial messages are logged as AVC (Access Vector Cache) denials. This
is the default mode that enforces SELinux security policy.
Permissive
The kernel does not enforce security policy rules but SELinux sends denial messages to
a log file. This allows you to see what actions would have been denied if SELinux were
running in enforcing mode. This mode is intended to used for diagnosing the behavior of
SELinux.
24.2.3 Setting SELinux Modes
You can set the default and current SELinux mode in the Status view of the SELinux Administration GUI.
Alternatively, to display the current mode, use the getenforce command:
# getenforce
Enforcing
To set the current mode to Enforcing, enter:
# setenforce Enforcing
To set the current mode to Permissive, enter:
# setenforce Permissive
The current value that you set for a mode using setenforce does not persist across reboots. To
configure the default SELinux mode, edit the configuration file for SELinux, /etc/selinux/config, and
set the value of the SELINUX directive to disabled, enabled, or permissive.
24.2.4 About SELinux Policies
An SELinux policy describes the access permissions for all users, programs, processes, and files, and
for the devices upon which they act. You can configure SELinux to implement either Targeted Policy or
Multilevel Security (MLS) Policy.
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About SELinux Policies
24.2.4.1 Targeted Policy
Applies access controls to a limited number of processes that are believed to be most likely to be the
targets of an attack on the system. Targeted processes run in their own SELinux domain, known as a
confined domain, which restricts access to files that an attacker could exploit. If SELinux detects that a
targeted process is trying to access resources outside the confined domain, it denies access to those
resources and logs the denial. Only specific services run in confined domains. Examples are services that
listen on a network for client requests, such as httpd, named, and sshd, and processes that run as root
to perform tasks on behalf of users, such as passwd. Other processes, including most user processes, run
in an unconfined domain where only DAC rules apply. If an attack compromises an unconfined process,
SELinux does not prevent access to system resources and data.
The following table lists examples of SELinux domains.
Domain
Description
initrc_t
init and processes executed by init
kernel_t
Kernel processes
unconfined_t
Processes executed by Oracle Linux users run in the unconfined
domain
24.2.4.2 Multilevel Security (MLS) Policy
Applies access controls to multiple levels of processes with each level having different rules for user
access. Users cannot obtain access to information if they do not have the correct authorization to run
a process at a specific level. In SELinux, MLS implements the Bell–LaPadula (BLP) model for system
security, which applies labels to files, processes and other system objects to control the flow of information
between security levels. In a typical implementation, the labels for security levels might range from the
most secure, top secret, through secret, and classified, to the least secure, unclassified. For
example, under MLS, you might configure a program labelled secret to be able to write to a file that is
labelled top secret, but not to be able to read from it. Similarly, you would permit the same program to
read from and write to a file labelled secret, but only to read classified or unclassified files. As
a result, information that passes through the program can flow upwards through the hierarchy of security
levels, but not downwards.
Note
You must install the selinux-policy-mls package if you want to be able to
apply the MLS policy.
24.2.4.3 Setting SELinux Policies
Note
You cannot change the policy type of a running system.
You can set the default policy type in the Status view of the SELinux Administration GUI.
Alternatively, to configure the default policy type, edit /etc/selinux/config and set the value of the
SELINUXTYPE directive to targeted or mls.
24.2.4.4 Customizing SELinux Policies
You can customize an SELinux policy by enabling or disabling the members of a set of boolean values.
Any changes that you make take effect immediately and do not require a reboot.
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About SELinux Context
You can set the boolean values in the Boolean view of the SELinux Administration GUI.
Alternatively, to display all boolean values together with a short description, use the following command:
# semanage boolean -l
SELinux boolean
State
ftp_home_dir
smartmon_3ware
xdm_sysadm_login
.
.
.
(off
(off
(off
Default Description
,
,
,
off)
off)
off)
Allow ftp to read and write files in the user home ...
Enable additional permissions needed to support dev...
Allow xdm logins as sysadm
You can use the getsebool and setsebool commands to display and set the value of a specific
boolean.
# getsebool boolean
# setsebool boolean on|off
For example, to display and set the value of the ftp_home_dir boolean:
# getsebool ftp_home_dir
ftp_home_dir --> off
# setsebool ftp_home_dir on
# getsebool ftp_home_dir
ftp_home_dir --> on
To toggle the value of a boolean, use the togglesebool command as shown in this example:
# togglesebool ftp_home_dir
ftp_home_dir: inactive
To make the value of a boolean persist across reboots, specify the -P option to setsebool, for example:
# setsebool -P ftp_home_dir on
# getsebool ftp_home_dir
ftp_home_dir --> on
24.2.5 About SELinux Context
Under SELinux, all file systems, files, directories, devices, and processes have an associated security
context. For files, SELinux stores a context label in the extended attributes of the file system. The context
contains additional information about a system object: the SELinux user, their role, their type, and the
security level. SELinux uses this context information to control access by processes, Linux users, and files.
You can specify the -Z option to certain commands (ls, ps, and id) to display the SELinux context with
the following syntax:
SELinux user:Role:Type:Level
where the fields are as follows:
SELinux user
An SELinux user account compliments a regular Linux user account. SELinux maps
every Linux user to an SELinux user identity that is used in the SELinux context for the
processes in a user session.
Role
In the Role-Based Access Control (RBAC) security model, a role acts as an intermediary
abstraction layer between SELinux process domains or file types and an SELinux
user. Processes run in specific SELinux domains, and file system objects are assigned
SELinux file types. SELinux users are authorized to perform specified roles, and roles
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About SELinux Context
are authorized for specified SELinux domains and file types. A user's role determines
which process domains and file types he or she can access, and hence, which
processes and files, he or she can access.
Type
A type defines an SELinux file type or an SELinux process domain. Processes are
separated from each other by running in their own domains. This separation prevents
processes from accessing files that other processes use, and prevents processes from
accessing other processes. The SELinux policy rules define the access that process
domains have to file types and to other process domains.
Level
A level is an attribute of Multilevel Security (MLS) and Multicategory Security (MCS).
An MLS range is a pair of sensitivity levels, written as low_level-high_level. The
range can be abbreviated as low_level if the levels are identical. For example, s0
is the same as s0-s0. Each level has an optional set of security categories to which it
applies. If the set is contiguous, it can be abbreviated. For example, s0:c0.c3 is the
same as s0:c0,c1,c2,c3.
24.2.5.1 Displaying SELinux User Mapping
To display the mapping between SELinux and Linux user accounts, select the User Mapping view in the
the SELinux Administration GUI.
Alternatively, enter the following command to display the user mapping:
# semanage login -l
Login Name
SELinux User
MLS/MCS Range
__default__
root
system_u
unconfined_u
unconfined_u
system_u
s0-s0:c0.c1023
s0-s0:c0.c1023
s0-s0:c0.c1023
By default, SELinux maps Linux users other than root and the default system-level user, system_u, to
the Linux __default__ user, and in turn to the SELinux unconfined_u user. The MLS/MCS Range is
the security level used by Multilevel Security (MLS) and Multicategory Security (MCS).
24.2.5.2 Displaying SELinux Context Information
To display the context information that is associated with files, use the ls -Z command:
# ls -Z
-rw-------.
drwx------.
-rw-r--r--.
-rw-r--r--.
root
root
root
root
root
root
root
root
system_u:object_r:admin_home_t:s0 anaconda-ks.cfg
unconfined_u:object_r:admin_home_t:s0 Desktop
system_u:object_r:admin_home_t:s0 install.log
system_u:object_r:admin_home_t:s0 install.log.syslog
To display the context information that is associated with a specified file or directory:
# ls -Z /etc/selinux/config
-rw-r--r--. root root system_u:object_r:selinux_config_t:s0 /etc/selinux/config
To display the context information that is associated with processes, use the ps -Z command:
# ps -Z
LABEL
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
PID
3038
3044
3322
TTY
pts/0
pts/0
pts/0
TIME
00:00:00
00:00:00
00:00:00
CMD
su
bash
ps
To display the context information that is associated with the current user, use the id -Z command:
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About SELinux Users
# id -Z
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
24.2.5.3 Changing the Default File Type
Under some circumstances, you might need to change the default file type for a file system hierarchy. For
example, you might want to use a DocumentRoot directory other than /var/www/html with httpd.
To change the default file type of the directory hierarchy /var/webcontent to httpd_sys_content_t:
1. Use the semanage command to define the file type httpd_sys_content_t for the directory
hierarchy:
# /usr/sbin/semanage fcontext -a -t httpd_sys_content_t "/var/webcontent(/.*)?"
This command adds the following entry to the file /etc/selinux/targeted/contexts/files/
file_contexts.local:
/var/webcontent(/.*)?
system_u:object_r:httpd_sys_content_t:s0
2. Use the restorecon command to apply the new file type to the entire directory hierarchy.
# /sbin/restorecon -R -v /var/webcontent
24.2.5.4 Restoring the Default File Type
To restore the default file type of the directory hierarchy /var/webcontent after previously changing it to
httpd_sys_content_t:
1. Use the semanage command to delete the file type definition for the directory hierarchy from the file /
etc/selinux/targeted/contexts/files/file_contexts.local:
# /usr/sbin/semanage fcontext -d "/var/webcontent(/.*)?"
2. Use the restorecon command to apply the default file type to the entire directory hierarchy.
# /sbin/restorecon -R -v /var/webcontent
24.2.5.5 Relabelling a File System
If you see an error message that contains the string file_t, the problem usually lies with a file system
having an incorrect context label.
To relabel a file system, use one of the following methods:
• In the Status view of the SELinux Administration GUI, select the Relabel on next reboot option.
• Create the file /.autorelabel and reboot the system.
• Run the fixfiles onboot command and reboot the system.
24.2.6 About SELinux Users
As described in Section 24.2.5, “About SELinux Context”, each SELinux user account compliments a
regular Oracle Linux user account. SELinux maps every Oracle Linux user to an SELinux user identity that
is used in the SELinux context for the processes in a user session.
SELinux users form part of a SELinux policy that is authorized for a specific set of roles and for a specific
MLS (Multi-Level Security) range, and each Oracle Linux user is mapped to an SELinux user as part of
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Troubleshooting Access-Denial Messages
the policy. As a result, Linux users inherit the restrictions and security rules and mechanisms placed on
SELinux users. To define the roles and levels of users, the mapped SELinux user identity is used in the
SELinux context for processes in a session. You can display user mapping in the User Mapping view of
the SELinux Administration GUI. You can also view the mapping between SELinux and Oracle Linux user
accounts from the command line:
# semanage login –l
Login Name
SELinux User
_default_
unconfined_u
root
unconfined_u
system_u
system_u
MLS/MCS Range
s0-s0:c0.c1023
s0-s0:c0.c1023
s0-s0:c0.c1023
The MLS/MCS Range column displays the level used by MLS and MCS.
By default, Oracle Linux users are mapped to the SELinux user unconfined_u.
You can configure SELinux to confine Oracle Linux users by mapping them to SELinux users in confined
domains, which have predefined security rules and mechanisms as listed in the following table.
SELinux User
SELinux
Domain
Permit
Running
su?
Permit Network Permit Logging Permit Executing
Access?
in Using
Applications in
X Window
$HOME and /tmp?
System?
guest_u
guest_t
No
No
No
No
staff_u
staff_t
Yes
Yes
Yes
Yes
user_u
user_t
No
Yes
Yes
Yes
xguest_x
xguest_t
No
Firefox only
Yes
No
24.2.6.1 Mapping Oracle Linux Users to SELinux Users
To map an Oracle Linux user oluser to an SELinux user such as user_u, use the semanage command:
# semanage login -a -s user_u oluser
24.2.6.2 Configuring the Behavior of Application Execution for Users
To help prevent flawed or malicious applications from modifying a user's files, you can use booleans to
specify whether users are permitted to run applications in directories to which they have write access, such
as in their home directory hierarchy and /tmp.
To allow Oracle Linux users in the guest_t and xguest_t domains to execute applications in directories
to which they have write access:
# setsebool -P allow_guest_exec_content on
# setsebool -P allow_xguest_exec_content on
To prevent Linux users in the staff_t and user_t domains from executing applications in directories to
which they have write access:
# setsebool -P allow_staff_exec_content off
# setsebool -P allow_user_exec_content off
24.2.7 Troubleshooting Access-Denial Messages
The decisions that SELinux has made about allowing denying access are stored in the Access Vector
Cache (AVC). If the auditing service (auditd) is not running, SELinux logs AVC denial messages to /
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About Packet-filtering Firewalls
var/log/messages. Otherwise, the messages are logged to /var/log/audit/audit.log. If the
setroubleshootd daemon is running, easier-to-read versions of the denial messages are also written to
/var/log/messages.
If you have installed the setroubleshoot and setroubleshoot-server packages, the auditd
and setroubleshoot services are running, and you are using the X Window System, you can use the
sealert -b command to run the SELinux Alert Browser, which displays information about SELinux AVC
denials. To view the details of the alert, click Show. To view a recommended solution, click Troubleshoot.
If you do not use the SELinux Alert Browser, you can search in /var/log/audit/audit.log for
messages containing the string denied, and in /var/log/messages for messages containing the string
SELinux is preventing. For example:
# grep denied /var/log/audit/audit.log
type=AVC msg=audit(1364486257.632:26178): avc: denied { read } for
pid=5177 comm="httpd" name="index.html" dev=dm-0 ino=396075
scontext=unconfined_u:system_r:httpd_t:s0
tcontext=unconfined_u:object_r:acct_data_t:s0 tclass=file
The main causes of access-denial problems are:
• The context labels for an application or file are incorrect.
A solution might be to change the default file type of the directory hierarchy. For example, change the
default file type from /var/webcontent to httpd_sys_content_t:
# /usr/sbin/semanage fcontext -a -t httpd_sys_content_t "/var/webcontent(/.*)?"
# /sbin/restorecon -R -v /var/webcontent
• A Boolean that configures a security policy for a service is set incorrectly.
A solution might be to change the value of a Boolean. For example, allow users' home directories to be
browsable by turning on httpd_enable_homedirs:
# setsebool -P httpd_enable_homedirs on
• A service attempts to access a port to which a security policy does not allow access.
If the service's use of the port is valid, a solution is to use semanage to add the port to the policy
configuration. For example, allow the Apache HTTP server to listen on port 8000:
# semanage port -a -t http_port_t -p tcp 8000
• An update to a package causes an application to behave in a way that breaks an existing security policy.
You can use the audit2allow -w -a command to view the reason why an access denial occurred.
If you then run the audit2allow -a -M module command, it creates a type enforcement (.te)
file and a policy package (.pp) file. You can use the policy package file with the semodule -i
module.pp command to stop the error from reoccurring. This procedure is usually intended to allow
package updates to function until an amended policy is available. If used incorrectly, it can create
potential security holes on your system.
24.3 About Packet-filtering Firewalls
Note
The iptables and system-config-firewall packages provide the
components of the packet-filtering firewall and the accompanying utilities.
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About Packet-filtering Firewalls
A packet filtering firewall filters incoming and outgoing network packets based on the packet header
information. You can create packet filter rules that determine whether packets are accepted or rejected.
For example, if you create a rule to block a port, any request is made to that port that is blocked by the
firewall, and the request is ignored. Any service that is listening on a blocked port is effectively disabled.
The Oracle Linux kernel uses the Netfilter feature to provide packet filtering functionality for IPv4 and IPv6
packets respectively.
Netfilter consists of two components:
• A netfilter kernel component consisting of a set of tables in memory for the rules that the kernel
uses to control network packet filtering.
• The iptables and ip6tables utilities to create, maintain, and display the rules that netfilter
stores.
To implement a simple, general-purpose firewall, you can use the Firewall Configuration GUI (systemconfig-firewall) to create basic Netfilter rules.
Figure 24.1 shows the Firewall Configuration GUI.
Figure 24.1 Firewall Configuration
To create a more complex firewall configuration, use the iptables and ip6tables utilities to configure
the packet filtering rules.
Netfilter records the packet filtering rules in the /etc/sysconfig/iptables and /etc/sysconfig/
ip6tables files, which netfilter reads when it is initialized.
The netfilter tables include:
Filter
The default table, which is mainly used to drop or accept packets based on their content.
Mangle
This table is used to alter certain fields in a packet.
324
Controlling the Firewall Service
NAT
The Network Address Translation table is used to route packets that create new connections.
The kernel uses the rules stored in these tables to make decisions about network packet filtering. Each
rule consists of one or more criteria and a single action. If a criterion in a rule matches the information in a
network packet header, the kernel applies the action to the packet. Examples of actions include:
ACCEPT
Continue processing the packet.
DROP
End the packet’s life without notice.
REJECT
As DROP, and additionally notify the sending system that the packet was blocked.
Rules are stored in chains, where each chain is composed of a default policy plus zero or more rules. The
kernel applies each rule in a chain to a packet until a match is found. If there is no matching rule, the kernel
applies the chain’s default action (policy) to the packet.
Each netfilter table has several predefined chains. The filter table contains the following chains:
FORWARD
Packets that are not addressed to the local system pass through this chain.
INPUT
Inbound packets to the local system pass through this chain.
OUTPUT
Locally created packets pass through this chain.
The chains are permanent and you cannot delete them. However, you can create additional chains in the
filter table.
For more information, see the iptables(8) and ip6tables(8) manual pages.
24.3.1 Controlling the Firewall Service
To start the firewall service (iptables) and configure it to start when the system boots, enter the following
commands:
# service iptables start
# chkconfig iptables on
To save any changes that you have made to the firewall rules to /etc/sysconfig/iptables and /
etc/sysconfig/ip6tables, so that the service loads them when it next starts:
# service iptables save
To restart the service so that it re-reads its rules from /etc/sysconfig/iptables and /etc/
sysconfig/ip6tables:
# service iptables restart
To stop the service:
# service iptables stop
24.3.2 Listing Firewall Rules
Use the iptables -L command to list firewall rules for the chains of the filter table. The following
example shows the default rules for a newly installed system:
# iptables -L
Chain INPUT (policy ACCEPT)
target
prot opt source
ACCEPT
all -- anywhere
destination
anywhere
325
state RELATED,ESTABLISHED
Inserting and Replacing Rules in a Chain
ACCEPT
ACCEPT
ACCEPT
ACCEPT
ACCEPT
ACCEPT
ACCEPT
REJECT
icmp
all
tcp
udp
udp
tcp
udp
all
---------
anywhere
anywhere
anywhere
anywhere
anywhere
anywhere
anywhere
anywhere
anywhere
anywhere
anywhere
anywhere
224.0.0.251
anywhere
anywhere
anywhere
state NEW tcp dpt:ssh
state NEW udp dpt:ipp
state NEW udp dpt:mdns
state NEW tcp dpt:ipp
state NEW udp dpt:ipp
reject-with icmp-host-prohibited
Chain FORWARD (policy ACCEPT)
target
prot opt source
REJECT
all -- anywhere
destination
anywhere
reject-with icmp-host-prohibited
Chain OUTPUT (policy ACCEPT)
target
prot opt source
destination
In this example, the default policy for each chain is ACCEPT. A more secure system could have a default
policy of DROP, and the additional rules would only allow specific packets on a case-by-case basis.
If you want to modify the chains, specify the --line-numbers option to see how the rules are numbered.
# iptables -L --line-numbers
Chain INPUT (policy ACCEPT)
num target
prot opt source
1
ACCEPT
all -- anywhere
2
ACCEPT
icmp -- anywhere
3
ACCEPT
all -- anywhere
4
ACCEPT
tcp -- anywhere
5
ACCEPT
udp -- anywhere
6
ACCEPT
udp -- anywhere
7
ACCEPT
tcp -- anywhere
8
ACCEPT
udp -- anywhere
9
REJECT
all -- anywhere
destination
anywhere
anywhere
anywhere
anywhere
anywhere
224.0.0.251
anywhere
anywhere
anywhere
Chain FORWARD (policy ACCEPT)
num target
prot opt source
1
REJECT
all -- anywhere
destination
anywhere
Chain OUTPUT (policy ACCEPT)
num target
prot opt source
destination
state RELATED,ESTABLISHED
state NEW tcp dpt:ssh
state NEW udp dpt:ipp
state NEW udp dpt:mdns
state NEW tcp dpt:ipp
state NEW udp dpt:ipp
reject-with icmp-host-prohibited
reject-with icmp-host-prohibited
24.3.3 Inserting and Replacing Rules in a Chain
Use the iptables -I command to insert a rule in a chain. For example, the following command inserts a
rule in the INPUT chain to allow access by TCP on port 80:
# iptables -I INPUT 4 -p tcp -m tcp --dport 80 -j ACCEPT
# iptables -L --line-numbers
Chain INPUT (policy ACCEPT)
num target
prot opt source
destination
1
ACCEPT
all -- anywhere
anywhere
2
ACCEPT
icmp -- anywhere
anywhere
3
ACCEPT
all -- anywhere
anywhere
4
ACCEPT
tcp -- anywhere
anywhere
5
ACCEPT
tcp -- anywhere
anywhere
6
ACCEPT
udp -- anywhere
anywhere
7
ACCEPT
udp -- anywhere
224.0.0.251
8
ACCEPT
tcp -- anywhere
anywhere
9
ACCEPT
udp -- anywhere
anywhere
10
REJECT
all -- anywhere
anywhere
Chain FORWARD (policy ACCEPT)
num target
prot opt source
1
REJECT
all -- anywhere
destination
anywhere
326
state RELATED,ESTABLISHED
tcp dpt:http
state NEW tcp dpt:ssh
state NEW udp dpt:ipp
state NEW udp dpt:mdns
state NEW tcp dpt:ipp
state NEW udp dpt:ipp
reject-with icmp-host-prohibited
reject-with icmp-host-prohibited
Deleting Rules in a Chain
Chain OUTPUT (policy ACCEPT)
num target
prot opt source
destination
The output from iptables -L shows that the new entry has been inserted as rule 4, and the old rules
4 through 9 are pushed down to positions 5 through 10. The TCP destination port of 80 is represented as
http, which corresponds to the following definition in the /etc/services file (the HTTP daemon listens
for client requests on port 80):
http
80/tcp
www www-http
# WorldWideWeb HTTP
To replace the rule in a chain, use the iptables -R command. For example, the following command
replaces rule 4 in the INPUT chain to allow access by TCP on port 443:
# iptables -I INPUT 4 -p tcp -m tcp --dport 443 -j ACCEPT
# iptables -L --line-numbers
Chain INPUT (policy ACCEPT)
num target
prot opt source
destination
1
ACCEPT
all -- anywhere
anywhere
2
ACCEPT
icmp -- anywhere
anywhere
3
ACCEPT
all -- anywhere
anywhere
4
ACCEPT
tcp -- anywhere
anywhere
...
state RELATED,ESTABLISHED
tcp dpt:https
The TCP destination port of 443 is represented as https, which corresponds to the following definition in
the /etc/services file for secure HTTP on port 443:
https
443/tcp
# http protocol over TLS/SSL
24.3.4 Deleting Rules in a Chain
Use the iptables -D command to delete a rule in a chain. For example, the following command deletes
rule 4 from the INPUT chain:
# iptables -D INPUT 4
To delete all rules in a chain, enter:
# iptables -F chain
To delete all rules in all chains, enter:
# iptables -F
24.3.5 Saving Rules
To save your changes to the firewall rules so that they are loaded when the iptables service next starts,
use the following command:
# service iptables save
The command saves the rules to /etc/sysconfig/iptables and /etc/sysconfig/ip6tables.
24.4 About TCP Wrappers
TCP wrappers provide basic filtering of incoming network traffic. You can allow or deny access from other
systems to certain wrapped network services running on a Linux server. A wrapped network service is one
that has been compiled against the libwrap.a library. You can use the ldd command to determine if a
network service has been wrapped as shown in the following example for the sshd daemon:
# ldd /usr/sbin/sshd | grep libwrap
libwrap.so.0 => /lib64/libwrap.so.0 (0x00007f877de07000)
327
About TCP Wrappers
When a remote client attempts to connect to a network service on the system, the wrapper consults the
rules in the configuration files /etc/hosts.allow and /etc/hosts.deny files to determine if access is
permitted.
The wrapper for a service first reads /etc/hosts.allow from top to bottom. If the daemon and client
combination matches an entry in the file, access is allowed. If the wrapper does not find a match in /etc/
hosts.allow, it reads /etc/hosts.deny from top to bottom. If the daemon and client combination
matches and entry in the file, access is denied. If no rules for the daemon and client combination are found
in either file, or if neither file exists, access to the service is allowed.
The wrapper first applies the rules specified in /etc/hosts.allow, so these rules take precedence over
the rules specified in /etc/hosts.deny. If a rule defined in /etc/hosts.allow permits access to a
service, any rule in /etc/hosts.deny that forbids access to the same service is ignored.
The rules take the following form:
daemon_list : client_list [: command] [: deny]
where daemon_list and client_list are comma-separated lists of daemons and clients, and
the optional command is run when a client tries to access a daemon. You can use the keyword ALL to
represent all daemons or all clients. Subnets can be represented by using the * wildcard, for example
192.168.2.*. Domains can be represented by prefixing the domain name with a period (.), for example
.mydomain.com. The optional deny keyword causes a connection to be denied even for rules specified in
the /etc/hosts.allow file.
The following are some sample rules.
Match all clients for scp, sftp, and ssh access (sshd).
sshd : ALL
Match all clients on the 192.168.2 subnet for FTP access (vsftpd).
vsftpd : 192.168.2.*
Match all clients in the mydomain.com domain for access to all wrapped services.
ALL : .mydomain.com
Match all clients for FTP access, and displays the contents of the banner file /etc/banners/vsftpd (the
banner file must have the same name as the daemon).
vsftpd : ALL : banners /etc/banners/
Match all clients on the 200.182.68 subnet for all wrapped services, and logs all such events. The %c and
%d tokens are expanded to the names of the client and the daemon.
ALL : 200.182.68.* : spawn /bin/echo `date` “Attempt by %c to connect to %d" >> /var/log/tcpwr.log
Match all clients for scp, sftp, and ssh access, and logs the event as an emerg message, which is
displayed on the console.
sshd : ALL : severity emerg
Match all clients in the forbid.com domain for scp, sftp, and ssh access, logs the event, and deny
access (even if the rule appears in /etc/hosts.allow).
sshd : .forbid.com : spawn /bin/echo `date` "sshd access denied for %c" >>/var/log/sshd.log : deny
For more information, see the hosts_access(5) manual page.
328
About chroot Jails
24.5 About chroot Jails
A chroot operation changes the apparent root directory for a running process and its children. It allows
you to run a program with a root directory other than /. The program cannot see or access files outside the
designated directory tree. Such an artificial root directory is called a chroot jail, and its purpose is to limit
the directory access of a potential attacker. The chroot jail locks down a given process and any user ID that
it is using so that all they see is the directory in which the process is running. To the process, it appears
that the directory in which it is running is the root directory.
Note
The chroot mechanism cannot defend against intentional tampering or low-level
access to system devices by privileged users. For example, a chroot root user
could create device nodes and mount file systems on them. A program can also
break out of a chroot jail if it can gain root privilege and use chroot() to change
its current working directory to the real root directory. For this reason, you should
ensure that a chroot jail does not contain any setuid or setgid executables that
are owned by root.
For a chroot process to be able to start successfully, you must populate the chroot directory with all
required program files, configuration files, device nodes, and shared libraries at their expected locations
relative to the level of the chroot directory.
24.5.1 Running DNS and FTP Services in a Chroot Jail
If the DNS name service daemon (named) runs in a chroot jail, any hacker that enters your system via a
BIND exploit is isolated to the files under the chroot jail directory. Installing the bind-chroot package
creates the /var/named/chroot directory, which becomes the chroot jail for all BIND files.
You can configure the vsftpd FTP server to automatically start chroot jails for clients. By default,
anonymous users are placed in a chroot jail. However, local users that access an vsftpd FTP server
are placed in their home directory. Specify the chroot_local_user=YES option in the /etc/vsftpd/
vsftpd.conf file to place local users in a chroot jail based on their home directory.
24.5.2 Creating a Chroot Jail
To create a chroot jail:
1. Create the directory that will become the root directory of the chroot jail, for example:
# mkdir /home/oracle/jail
2. Use the ldd command to find out which libraries are required by the command that you intend to run in
the chroot jail, for example /bin/bash:
# ldd /bin/bash
linux-vdso.so.1 => (0x00007fff56fcc000)
libtinfo.so.5 => /lib64/libtinfo.so.5 (0x0000003ad1200000)
libdl.so.2 => /lib64/libdl.so.2 (0x0000003abe600000)
libc.so.6 => /lib64/libc.so.6 (0x0000003abe200000)
/lib64/ld-linux-x86-64.so.2 (0x0000003abde00000)
3. Create subdirectories of the chroot jail's root directory that have the same relative paths as the
command binary and its required libraries have to the real root directory, for example:
# mkdir /home/oracle/jail/bin
# mkdir /home/oracle/jail/lib64
329
Using a Chroot Jail
4. Copy the binary and the shared libraries to the directories under the chroot jail's root directory, for
example:
# cp /bin/bash /home/oracle/jail/bin
# cp /lib64/{libtinfo.so.5,libdl.so.2,libc.so.6,ld-linux-x86-64.so.2} \
/home/oracle/jail/lib64
24.5.3 Using a Chroot Jail
To run a command in a chroot jail in an existing directory (chroot_jail), use the following command:
# chroot chroot_jail command
If you do not specify a command argument, chroot runs the value of the SHELL environment variable or /
bin/sh if SHELL is not set.
For example, to run /bin/bash in a chroot jail (having previously set it up as described in Section 24.5.2,
“Creating a Chroot Jail”):
# chroot /home/oracle/jail
bash-4.1# pwd
/
bash-4.1# ls
bash: ls: command not found
bash-4.1# exit
exit
#
You can run built-in shell commands such as pwd in this shell, but not other commands unless you have
copied their binaries and any required shared libraries to the chroot jail.
For more information, see the chroot(1) manual page.
24.6 About Auditing
Auditing collects data at the kernel level that you can analyze to identify unauthorized activity. Auditing
collects more data in greater detail than system logging, but most audited events are uninteresting
and insignificant. The process of examining audit trails to locate events of interest can be a significant
challenge that you will probably need to automate.
The audit configuration file, /etc/audit/auditd.conf, defines the data retention policy, the maximum
size of the audit volume, the action to take if the capacity of the audit volume is exceeded, and the
locations of local and remote audit trail volumes. The default audit trail volume is /var/log/audit/
audit.log. For more information, see the auditd.conf(5) manual page.
By default, auditing captures specific events such as system logins, modifications to accounts, and sudo
actions. You can also configure auditing to capture detailed system call activity or modifications to certain
files. The kernel audit daemon (auditd) records the events that you configure, including the event type, a
time stamp, the associated user ID, and success or failure of the system call.
The entries in the audit rules file, /etc/audit/audit.rules, determine which events are audited. Each
rule is a command-line option that is passed to the auditctl command. You should typically configure
this file to match your site's security policy.
The following are examples of rules that you might set in the /etc/audit/audit.rules file.
Record all unsuccessful exits from open and truncate system calls for files in the /etc directory
hierarchy.
-a exit,always -S open -S truncate -F /etc -F success=0
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About System Logging
Record all files opened by a user with UID 10.
-a exit,always -S open -F uid=10
Record all files that have been written to or that have their attributes changed by any user who originally
logged in with a UID of 500 or greater.
-a exit,always -S open -F auid>=500 -F perm=wa
Record requests for write or file attribute change access to /etc/sudoers, and tag such record with the
string sudoers-change.
-w /etc/sudoers -p wa -k sudoers-change
Record requests for write and file attribute change access to the /etc directory hierarchy.
-w /etc/ -p wa
Require a reboot after changing the audit configuration. If specified, this rule should appear at the end of
the /etc/audit/audit.rules file.
-e 2
You can find more examples of audit rules in /usr/share/doc/audit-version/stig.rules, and in
the auditctl(8) and audit.rules(7) manual pages.
Stringent auditing requirements can impose a significant performance overhead and generate large
amounts of audit data. Some site security policies stipulate that a system must shut down if events cannot
be recorded because the audit volumes have exceeded their capacity. As a general rule, you should direct
audit data to separate file systems in rotation to prevent overspill and to facilitate backups.
You can use the -k option to tag audit records so that you can locate them more easily in an audit volume
with the ausearch command. For example, to examine records tagged with the string sudoers-change,
you would enter:
# ausearch -k sudoers-change
The aureport command generates summaries of audit data. You can set up cron jobs that run
aureport periodically to generate reports of interest. For example, the following command generates a
reports that shows every login event from 1 second after midnight on the previous day until the current
time:
# aureport -l -i -ts yesterday -te now
For more information, see the ausearch(8) and aureport(8) manual pages.
24.7 About System Logging
The log files contain messages about the system, kernel, services, and applications. For those files
that are controlled by the system logging daemon rsyslogd, the main configuration file is /etc/
rsyslog.conf, which contains global directives, module directives, and rules.
Global directives specify configuration options that apply to the rsyslogd daemon. All configuration
directives must start with a dollar sign ($) and only one directive can be specified on each line. The
following example specifies the maximum size of the rsyslog message queue:
$MainMsgQueueSize 50000
The available configuration directives are described in the file /usr/share/doc/rsyslog-versionnumber/rsyslog_conf_global.html.
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About System Logging
The design of rsyslog allows its functionality to be dynamically loaded from modules, which provide
configuration directives. To load a module, specify the following directive:
$ModLoad MODULE_name
Modules have the following main categories:
• Input modules gather messages from various sources. Input module names always start with the im
prefix (examples include imfile and imrelp).
• Filter modules allow rsyslogd to filter messages according to specified rules. The name of a filter
module always starts with the fm prefix.
• Library modules provide functionality for other loadable modules. rsyslogd loads library modules
automatically when required. You cannot configure the loading of library modules.
• Output modules provide the facility to store messages in a database or on other servers in a network, or
to encrypt them. Output module names always starts with the om prefix (examples include omsnmp and
omrelp).
• Message modification modules change the content of an rsyslog message.
• Parser modules allow rsyslogd to parse the message content of messages that it receives. The name
of a parser module always starts with the pm prefix.
• String generator modules generate strings based on the content of messages in cooperation with
rsyslog's template feature. The name of a string generator module always starts with the sm prefix.
Input modules receive messages, which pass them to one or more parser modules. A parser module
creates a representation of a message in memory, possibly modifying the message, and passes the
internal representation to output modules, which can also modify the content before outputting the
message.
A description of the available modules can be found at http://www.rsyslog.com/doc/
rsyslog_conf_modules.html.
An rsyslog rule consists of a filter part, which selects a subset of messages, and an action part,
which specifies what to do with the selected messages. To define a rule in the /etc/rsyslog.conf
configuration file, specify a filter and an action on a single line, separated by one or more tabs or spaces.
You can configure rsyslog to filter messages according to various properties. The most commonly used
filters are:
• Expression-based filters, written in the rsyslog scripting language, select messages according to
arithmetic, boolean, or string values.
• Facility/priority-based filters filter messages based on facility and priority values that take the form
facility.priority.
• Property-based filters filter messages by properties such as timegenerated or syslogtag.
The following table lists the available facility keywords for facility/priority-based filters:
Facility Keyword
Description
auth, authpriv
Security, authentication, or authorization messages.
cron
crond messages.
daemon
Messages from system daemons other than crond and rsyslogd.
332
About System Logging
Facility Keyword
Description
kern
Kernel messages.
lpr
Line printer subsystem.
mail
Mail system.
news
Network news subsystem.
syslog
Messages generated internally by rsyslogd.
user
User-level messages.
UUCP
UUCP subsystem.
local0 - local7
Local use.
The following table lists the available priority keywords for facility/priority-based filters, in ascending order
of importance:
Priority Keyword
Description
debug
Debug-level messages.
info
Informational messages.
notice
Normal but significant condition.
warning
Warning conditions.
err
Error conditions.
crit
Critical conditions.
alert
Immediate action required.
emerg
System is unstable.
All messages of the specified priority and higher are logged according to the specified action. An asterisk
(*) wildcard specifies all facilities or priorities. Separate the names of multiple facilities and priorities on a
line with commas (,). Separate multiple filters on one line with semicolons (;). Precede a priority with an
exclamation mark (!) to select all messages except those with that priority.
The following are examples of facility/priority-based filters.
Select all kernel messages with any priority.
kern.*
Select all mail messages with crit or higher priority.
mail.crit
Select all daemon and kern messages with warning or err priority.
daemon,kern.warning,err
Select all cron messages except those with info or debug priority.
cron.!info,!debug
By default, /etc/rsyslog.conf includes the following rules:
# Log all kernel messages to the console.
# Logging much else clutters up the screen.
#kern.*
# Log anything (except mail) of level info or higher.
# Don't log private authentication messages!
333
/dev/console
Configuring Logwatch
*.info;mail.none;authpriv.none;cron.none
/var/log/messages
# The authpriv file has restricted access.
authpriv.*
/var/log/secure
# Log all the mail messages in one place.
mail.*
-/var/log/maillog
# Log cron stuff
cron.*
/var/log/cron
# Everybody gets emergency messages
*.emerg
*
# Save news errors of level crit and higher in a special file.
uucp,news.crit
/var/log/spooler
# Save boot messages also to boot.log
local7.*
/var/log/boot.log
You can send the logs to a central log server over TCP by adding the following entry to the forwarding
rules section of /etc/rsyslog.conf on each log client:
*.*
@@logsvr:port
where logsvr is the domain name or IP address of the log server and port is the port number (usually,
514).
On the log server, add the following entry to the MODULES section of /etc/rsyslog.conf:
$ModLoad imtcp
$InputTCPServerRun port
where port corresponds to the port number that you set on the log clients.
To manage the rotation and archival of the correct logs, edit /etc/logrotate.d/syslog so that it
references each of the log files that are defined in the RULES section of /etc/rsyslog.conf. You can
configure how often the logs are rotated and how many past copies of the logs are archived by editing /
etc/logrotate.conf.
It is recommended that you configure Logwatch on your log server to monitor the logs for suspicious
messages, and disable Logwatch on log clients. However, if you do use Logwatch, disable high precision
timestamps by adding the following entry to the GLOBAL DIRECTIVES section of /etc/rsyslog.conf
on each system:
$ActionFileDefaultTemplate RSYSLOG_TraditionalFileFormat
For more information, see the logrotate(8), logwatch(8), rsyslogd(8) and rsyslog.conf(5)
manual pages, the HTML documentation in the /usr/share/doc/rsyslog-5.8.10 directory, and the
documentation at http://www.rsyslog.com/doc/manual.html.
24.7.1 Configuring Logwatch
Logwatch is a monitoring system that you can configure to report on areas of interest in the system logs.
After you install the logwatch package, the /etc/cron.daily/0logwatch script runs every night
and sends an email report to root. You can set local configuration options in /etc/logwatch/conf/
logwatch.conf that override the main configuration file /usr/share/logwatch/default.conf/
logwatch.conf, including:
• Log files to monitor, including log files that are stored for other hosts.
• Names of services to monitor, or to be excluded from monitoring.
334
About Process Accounting
• Level of detail to report.
• User to be sent an emailed report.
You can also run logwatch directly from the command line.
For more information, see the logwatch(8) manual page.
24.8 About Process Accounting
The psacct package implements the process accounting service in addition to the following utilities that
you can use to monitor process activities:
ac
Displays connection times in hours for a user as recorded in the wtmp file (by default, /var/
log/wtmp).
accton
Turns on process accounting to the specified file. If you do not specify a file name argument,
process accounting is stopped. The default system accounting file is /var/account/pacct.
lastcomm
Displays information about previously executed commands as recorded in the system
accounting file.
sa
Summarizes information about previously executed commands as recorded in the system
accounting file.
Note
As for any logging activity, ensure that the file system has enough space to
store the system accounting and wtmp files. Monitor the size of the files and, if
necessary, truncate them.
For more information, see the ac(1), accton(8), lastcomm(1), and sa(8) manual pages.
24.9 Security Guidelines
The following sections provide guidelines that help secure your Oracle Linux system.
24.9.1 Minimizing the Software Footprint
On systems on which Oracle Linux has been installed, remove unneeded RPMs to minimize the software
footprint. For example, you could uninstall the X Windows package (xorg-x11-server-Xorg) if it is not
required on a server system.
To discover which package provides a given command or file, use the yum provides command as
shown in the following example:
# yum provides /usr/sbin/sestatus
...
policycoreutils-2.0.83-19.24.0.1.el6.x86_64 : SELinux policy core utilities
Repo
: installed
Matched from:
Other
: Provides-match: /usr/sbin/sestatus
To display the files that a package provides, use the repoquery utility, which is included in the yumutils package. For example, the following command lists the files that the btrfs-progs package
provides.
# repoquery -l btrfs-progs
/sbin/btrfs
/sbin/btrfs-convert
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Minimizing the Software Footprint
/sbin/btrfs-debug-tree
.
.
.
To uninstall a package, use the yum remove command, as shown in this example:
# yum remove xinetd
Loaded plugins: refresh-packagekit, security
Setting up Remove Process
Resolving Dependencies
--> Running transaction check
---> Package xinetd.x86_64 2:2.3.14-35.el6_3 will be erased
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package
Arch
Version
Repository
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Complete!
The following table lists packages that you should not install or that you should remove using yum remove
if they are already installed.
Package
Description
krb5-appl-clients
Kerberos versions of ftp, rcp, rlogin, rsh and telnet. If
possible, use SSH instead.
rsh, rsh-server
rcp, rlogin, and rsh use unencrypted communication that
can be snooped. Use SSH instead.
samba
Network services used by Samba. Remove this package if the
system is not acting as an Active Directory server, a domain
controller, or as a domain member, and it does not provide
Microsoft Windows file and print sharing functionality.
talk, talk-server
talk is considered obsolete.
telnet, telnet-server
telnet uses unencrypted communication that can be
snooped. Use SSH instead.
tftp, tftp-server
TFTP uses unencrypted communication that can be snooped.
Use only if required to support legacy hardware. If possible,
use SSH or other secure protocol instead.
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Configuring System Logging
Package
Description
xinetd
The security model used by the Internet listener daemon is
deprecated.
ypbind, ypserv
The security model used by NIS is inherently flawed. Use an
alternative such as LDAP or Kerberos instead.
24.9.2 Configuring System Logging
Verify that the system logging service rsyslog is running:
# service rsyslog status
rsyslogd (pid 1632) is running...
If the service is not running, start it and enable it to start when the system is rebooted:
# service rsyslog start
# chkconfig rsyslog on
Ensure that each log file referenced in /etc/rsyslog.conf exists and is owned and only readable by
root:
# touch logfile
# chown root:root logfile
# chmod 0600 logfile
It is also recommended that you use a central log server and that you configure Logwatch on that server.
See Section 24.7, “About System Logging”.
24.9.3 Disabling Core Dumps
Core dumps can contain information that an attacker might be able to exploit and they take up a large
amount of disk space. To prevent the system creating core dumps when the operating system terminates a
program due to a segment violation or other unexpected error, add the following line to /etc/security/
limits.conf:
*
hard
core
0
You can restrict access to core dumps to certain users or groups, as described in the limits.conf(5)
manual page.
By default, the system prevents setuid and setgid programs, programs that have changed credentials,
and programs whose binaries do not have read permission from dumping core. To ensure that the setting
is permanently recorded, add the following lines to /etc/sysctl.conf:
# Disallow core dumping by setuid and setgid programs
fs.suid_dumpable = 0
and then run the sysctl -p command.
Note
A value of 1 permits core dumps that are readable by the owner of the dumping
process. A value of 2 permits core dumps that are readable only by root for
debugging purposes.
24.9.4 Minimizing Active Services
Restrict services to only those that a server requires. The default installation for an Oracle Linux server
configures a minimal set of services:
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Minimizing Active Services
cupsd and lpd (print services)
sendmail (email delivery service)
sshd (openSSH services)
If possible, configure one type of service per physical machine, virtual machine, or Linux Container. This
technique limits exposure if a system is compromised.
If a service is not used, remove the software packages that are associated with the service. If it is not
possible to remove a service because of software dependencies, use the chkconfig and service
commands to disable the service.
For services that are in use, apply the latest Oracle support patches and security updates to keep software
packages up to date. To protect against unauthorized changes, ensure that the /etc/services file is
owned by root and writable only by root.
# ls -Z /etc/services
-rw-r--r--. root root system_u:object_r:etc_t:SystemLow /etc/services
Unless specifically stated otherwise, consider disabling the services in the following table if they are not
used on your system:
Service
Description
anacron
Executes commands periodically. Primarily intended for use on laptop and user
desktop machines that do not run continuously.
apmd
(Advanced Power Management Daemon) Provides information on power
management and battery status, and allows programmed response to power
management events. Primarily intended for use on laptop machines.
automount
Manages mount points for the automatic file-system mounter. Disable this
service on servers that do not require automounter functionality.
bluetooth
Supports the connections of Bluetooth devices. Primarily intended for use on
laptop and user desktop machines. Bluetooth provides an additional potential
attack surface. Disable this service on servers that do not require Bluetooth
functionality.
firstboot
Configures a system when you first log in after installation. Controlled by the
/etc/rc.d/init.d/firstboot script. firstboot does not run unless
RUN_FIRSTBOOT=YES is set in /etc/sysconfig/firstboot. If /etc/
reconfigSys exists or if you specify reconfig in the kernel boot arguments,
firstboot runs in reconfiguration mode. Disable this service on servers
following successful installation.
gpm
(General Purpose Mouse) Provides support for the mouse pointer in a text
console.
haldaemon
(Hardware Abstraction Layer Daemon) Maintains a real-time database of the
devices that are connected to a system. Applications can use the HAL API to
discover and interact with newly attached devices. Primarily intended for use
on laptop and user desktop machines to support hot-plug devices.
Caution
Do not disable this service. Many applications rely on
this functionality.
hidd
(Bluetooth Human Interface Device daemon) Provides support for Bluetooth
input devices such as a keyboard or mouse. Primarily intended for use on
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Minimizing Active Services
Service
Description
laptop and user desktop machines. Bluetooth provides an additional potential
attack surface. Disable this service on servers that do not require Bluetooth
functionality.
irqbalance
Distributes hardware interrupts across processors on a multiprocessor system.
Disable this service on servers that do not require this functionality.
iscsi
Controls logging in to iSCSI targets and scanning of iSCSI devices. Disable this
service on servers that do not access iSCSI devices.
iscsid
Implements control and management for the iSCSI protocol. Disable this
service on servers that do not access iSCSI devices.
kdump
Allows a kdump kernel to be loaded into memory at boot time or a kernel dump
to be saved if the system panics. Disable this service on servers that you do
not use for debugging or testing.
mcstrans
Controls the SELinux Context Translation System service.
mdmonitor
Checks the status of all software RAID arrays on the system. Disable this
service on servers that do not use software RAID.
messagebus
Broadcasts notifications of system events and other messages relating to
hardware events via the system-wide D-BUS message bus.
Caution
Do not disable this service. Many applications rely on
this functionality.
microcode_ctl
Runs microcode that is required for IA32 processors only. Disable this service
on servers that do not have such processors.
pcscd
(PC/SC Smart Card Daemon) Supports communication with smart-card
readers. Primarily intended for use on laptop and user desktop machines to
support smart-card authentication. Disable this service on servers that do not
use smart-card authentication.
sandbox
Sets up /tmp, /var/tmp, and home directories to be used with the
pam_namespace, sandbox, and xguest application confinement utilities.
Disable this service if you do not use these programs.
setroubleshoot
Controls the SELinux Troubleshooting service, which provides information
about SELinux Access Vector Cache (AVC) denials to the sealert tool.
smartd
Communicates with the Self-Monitoring, Analysis and Reporting Technology
(SMART) systems that are integrated into many ATA-3 and later, and SCSI-3
disk drives. SMART systems monitor disk drives to measure reliability, predict
disk degradation and failure, and perform drive testing.
xfs
Caches fonts in memory to improve the performance of X Window System
applications.
You should consider disabling the following network services if they are not used on your system:
Service
Description
avahi-daemon
Implements Apple's Zero configuration networking (also known as Rendezvous
or Bonjour). Primarily intended for use on laptop and user desktop machines
to support music and file sharing. Disable this service on servers that do not
require this functionality.
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Locking Down Network Services
Service
Description
cups
Implements the Common UNIX Printing System. Disable this service on
servers that do not need to provide this functionality.
hplip
Implements HP Linux Imaging and Printing to support faxing, printing, and
scanning operations on HP inkjet and laser printers. Disable this service on
servers that do not require this functionality.
isdn
(Integrated Services Digital Network) Provides support for network connections
over ISDN devices. Disable this service on servers that do not directly control
ISDN devices.
netfs
Mounts and unmounts network file systems, including NCP, NFS, and SMB.
Disable this service on servers that do not require this functionality.
network
Activates all network interfaces that are configured to start at boot time.
NetworkManager
Switches network connections automatically to use the best connection that is
available.
nfslock
Implements the Network Status Monitor (NSM) used by NFS. Disable this
service on servers that do not require this functionality.
nmb
Provides NetBIOS name services used by Samba. Disable this service and
remove the samba package if the system is not acting as an Active Directory
server, a domain controller, or as a domain member, and it does not provide
Microsoft Windows file and print sharing functionality.
portmap
Implements Remote Procedure Call (RPC) support for NFS. Disable this
service on servers that do not require this functionality.
rhnsd
Queries the Unbreakable Linux Network (ULN) for updates and information.
rpcgssd
Used by NFS. Disable this service on servers that do not require this
functionality.
rpcidmapd
Used by NFS. Disable this service on servers that do not require this
functionality.
smb
Provides SMB network services used by Samba. Disable this service and
remove the samba package if the system is not acting as an Active Directory
server, a domain controller, or as a domain member, and it does not provide
Microsoft Windows file and print sharing functionality.
To stop a service and prevent it from starting when you reboot the system, used the following commands:
# service service_name stop
# chkconfig service_name off
Alternatively, use the Service Configuration GUI (system-config-services) to configure services.
24.9.5 Locking Down Network Services
Note
It is recommended that you do not install the xinetd Internet listener daemon.
If you do not need this service, remove the package altogether by using the yum
remove xinetd command.
If you must enable xinetd on your system, minimize the network services that xinetd can launch by
disabling those services that are defined in the configuration files in /etc/xinetd.d and which are not
needed.
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Configuring a Packet-filtering Firewall
To counter potential Denial of Service (DoS) attacks, you can configure the resource limits for such
services by editing /etc/xinetd.conf and related configuration files. For example, you can set limits for
the connection rate, the number of connection instances to a service, and the number of connections from
an IP address:
# Maximum number of connections per second and
# number of seconds for which a service is disabled
# if the maximum number of connections is exceeded
cps
= 50 10
# Maximum number of connections to a service
instances
= 50
# Maximum number of connections from an IP address
per_source
= 10
For more information, see the xinetd(8) and /etc/xinetd.conf(5) manual pages.
24.9.6 Configuring a Packet-filtering Firewall
You can configure the Netfilter feature to act as a packet-filtering firewall that uses rules to determine
whether network packets are received, dropped, or forwarded.
The primary interfaces for configuring the packet-filter rules are the iptables and ip6tables utilities
and the Firewall Configuration Tool GUI (system-config-firewall). By default, the rules should drop
any packets that are not destined for a service that the server hosts or that originate from networks other
than those to which you want to allow access.
In addition, Netfilter provides Network Address Translation (NAT) to hide IP addresses behind a public IP
address, and IP masquerading to alter IP header information for routed packets. You can also set rulebased packet logging and define a dedicated log file in /etc/syslog.conf.
For more information, see Section 24.3, “About Packet-filtering Firewalls”.
24.9.7 Configuring TCP Wrappers
The TCP wrappers feature mediates requests from clients to services, and control access based on rules
that you define in the /etc/hosts.deny and /etc/hosts.allow files. You can restrict and permit
service access for specific hosts or whole networks. A common way of using TCP wrappers is to detect
intrusion attempts. For example, if a known malicious host or network attempts to access a service, you
can deny access and send a warning message about the event to a log file or to the system console.
For more information, see Section 24.4, “About TCP Wrappers”.
24.9.8 Configuring Kernel Parameters
You can use several kernel parameters to counteract various kinds of attack.
kernel.randomize_va_space controls Address Space Layout Randomization (ASLR), which can help
defeat certain types of buffer overflow attacks. A value of 0 disables ASLR, 1 randomizes the positions of
the stack, virtual dynamic shared object (VDSO) page, and shared memory regions, and 2 randomizes
the positions of the stack, VDSO page, shared memory regions, and the data segment. The default and
recommended setting is 2.
net.ipv4.conf.all.accept_source_route controls the handling of source-routed packets, which
might have been generated outside the local network. A value of 0 rejects such packets, and 1 accepts
them. The default and recommended setting is 0.
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Restricting Access to SSH Connections
net.ipv4.conf.all.rp_filter controls reversed-path filtering of received packets to counter IP
address spoofing. A value of 0 disables source validation, 1 causes packets to be dropped if the routing
table entry for their source address does not match the network interface on which they arrive, and 2
causes packets to be dropped if source validation by reversed path fails (see RFC 1812). The default
setting is 0. A value of 2 can cause otherwise valid packets to be dropped if the local network topology is
complex and RIP or static routes are used.
net.ipv4.icmp_echo_ignore_broadcasts controls whether ICMP broadcasts are ignored to protect
against Smurf DoS attacks. A value of 1 ignores such broadcasts, and 0 accepts them. The default and
recommended setting is 1.
net.ipv4.icmp_ignore_bogus_error_message controls whether ICMP bogus error message
responses are ignored. A value of 1 ignores such messages, and 0 accepts them. The default and
recommended setting is 1.
To change the value of a kernel parameter, add the setting to /etc/sysctl.conf, for example:
kernel.randomize_va_space = 1
and then run the sysctl -p command.
24.9.9 Restricting Access to SSH Connections
The Secure Shell (SSH) allows protected, encrypted communication with other systems. As SSH
is an entry point into the system, disable it if it is not required, or alternatively, edit the /etc/ssh/
sshd_config file to restrict its use.
For example, the following setting does not allow root to log in using SSH:
PermitRootLogin no
You can restrict remote access to certain users and groups by specifying the AllowUsers,
AllowGroups, DenyUsers, and DenyGroups settings, for example:
DenyUsers carol dan
AllowUsers alice bob
The ClientAliveInterval and ClientAliveCountMax settings cause the SSH client to time out
automatically after a period of inactivity, for example:
# Disconnect client after 300 seconds of inactivity
ClientAliveCountMax 0
ClientAliveInterval 300
After making changes to the configuration file, restart the sshd service for your changes to take effect.
For more information, see the sshd_config(5) manual page.
24.9.10 Configuring File System Mounts, File Permissions, and File
Ownerships
Use separate disk partitions for operating system and user data to prevent a file system full issue from
impacting the operation of a server. For example, you might create separate partitions for /home, /tmp, p,
/oracle, and so on.
Establish disk quotas to prevent a user from accidentally or intentionally filling up a file system and denying
access to other users.
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Configuring File System Mounts, File Permissions, and File Ownerships
To prevent the operating system files and utilities from being altered during an attack, mount the /usr file
system read-only. If you need to update any RPMs on the file system, use the -o remount,rw option
with the mount command to remount /usr for both read and write access. After performing the update,
use the -o remount,ro option to return the /usr file system to read-only mode.
To limit user access to non-root local file systems such as /tmp or removable storage partitions, specify
the -o noexec, nosuid, nodev options to mount. These option prevent the execution of binaries (but
not scripts), prevent the setuid bit from having any effect, and prevent the use of device files.
Use the find command to check for unowned files and directories on each file system, for example:
# find mount_point -mount -type f -nouser -o -nogroup -exec ls -l {} \;
# find mount_point -mount -type d -nouser -o -nogroup -exec ls -l {} \;
Unowned files and directories might be associated with a deleted user account, they might indicate an
error with software installation or deleting, or they might a sign of an intrusion on the system. Correct
the permissions and ownership of the files and directories that you find, or remove them. If possible,
investigate and correct the problem that led to their creation.
Use the find command to check for world-writable directories on each file system, for example:
# find mount_point -mount -type d -perm /o+w -exec ls -l {} \;
Investigate any world-writable directory that is owned by a user other than a system user. The user can
remove or change any file that other users write to the directory. Correct the permissions and ownership of
the directories that you find, or remove them.
You can also use find to check for setuid and setgid executables.
# find path -type f \( -perm -4000 -o -perm -2000 \) -exec ls -l {} \;
If the setuid and setgid bits are set, an executable can perform a task that requires other rights, such
as root privileges. However, buffer overrun attacks can exploit such executables to run unauthorized code
with the rights of the exploited process.
If you want to stop a setuid and setgid executable from being used by non-root users, you can use
the following commands to unset the setuid or setgid bit:
# chmod u-s file
# chmod g-s file
For example, you could use the chmod command to unset the setuid bit for the /bin/ping6 command:
# ls -al /bin/ping6
-rwsr-xr-x. 1 root root 36488 May 20
# chmod u-s /bin/ping6
# ls -al /bin/ping6
-rwxr-xr-x. 1 root root 36488 May 20
2011 /bin/ping6
2011 /bin/ping6
The following table lists programs for which you might want to consider unsetting setuid and setgid:
Program File
Bit Set
Description of Usage
/bin/ping
setuid
Sends an ICMP ECHO_REQUEST to a network host.
/bin/ping6
setuid
Sends an ICMPv6 ECHO_REQUEST to a network host.
/bin/cgexec
setgid
Runs a task in a control group.
/sbin/mount.nfs
setuid
Mounts an NFS file system.
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Checking User Accounts and Privileges
Program File
Bit Set
Description of Usage
Note
/sbin/mount.nfs4, /sbin/
umount.nfs, and /sbin/
umount.nfs4 are symbolic links to this
file.
/sbin/netreport
setgid
Requests notification of changes to network interfaces.
/usr/bin/chage
setuid
Finds out password aging information (via the -l option).
/usr/bin/chfn
setuid
Changes finger information.
/usr/bin/chsh
setuid
Changes the login shell.
/usr/bin/crontab
setuid
Edits, lists, or removes a crontab file.
/usr/bin/wall
setgid
Sends a system-wide message.
/usr/bin/write
setgid
Sends a message to another user.
/usr/bin/Xorg
setuid
Invokes the X Windows server.
/usr/libexec/openssh/
ssh-keysign
setuid
Runs the SSH helper program for host-based authentication.
/usr/sbin/suexec
setuid
Switches user before executing external CGI and SSI
programs. This program is intended to be used by the
Apache HTTP server. For more information, see http://
httpd.apache.org/docs/2.2/suexec.html.
/usr/sbin/usernetctl
setuid
Controls network interfaces. Permission for a user to alter the
state of a network inerface also requires USERCTL=yes to be
set in the interface file. You can also grant users and groups
the privilege to run the ip command by creating a suitable
entry in the /etc/sudoers file.
Note
This list is not exhaustive as many optional packages contain setuid and setgid
programs.
24.9.11 Checking User Accounts and Privileges
Check the system for unlocked user accounts on a regular basis, for example using a command such as
the following:
# for u in `cat /etc/passwd | cut -d: -f1 | sort`; do passwd -S $u; done
abrt LK 2012-06-28 0 99999 7 -1 (Password locked.)
adm LK 2011-10-13 0 99999 7 -1 (Alternate authentication scheme in use.)
apache LK 2012-06-28 0 99999 7 -1 (Password locked.)
avahi LK 2012-06-28 0 99999 7 -1 (Password locked.)
avahi-autoipd LK 2012-06-28 0 99999 7 -1 (Password locked.)
bin LK 2011-10-13 0 99999 7 -1 (Alternate authentication scheme in use.)
...
In the output from this command, the second field shows if a user account is locked (LK), does not have a
password (NP), or has a valid password (PS). The third field shows the date on which the user last changed
their password. The remaining fields show the minimum age, maximum age, warning period, and inactivity
period for the password and additional information about the password's status. The unit of time is days.
Use the passwd command to set passwords on any accounts that are not protected.
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Checking User Accounts and Privileges
Use passwd -l to lock unused accounts. Alternatively, use userdel to remove the accounts entirely.
For more information, see the passwd(1) and userdel(8) manual pages.
To specify how users' passwords are aged, edit the following settings in the /etc/login.defs file:
Setting
Description
PASS_MAX_DAYS
Maximum number of days for which a password can be used before it must be
changed. The default value is 99,999 days.
PASS_MIN_DAYS
Minimum number of days that is allowed between password changes. The
default value is 0 days.
PASS_WARN_AGE
Number of days warning that is given before a password expires. The default
value is 7 days.
For more information, see the login.defs(5) manual page.
To change how long a user's account can be inactive before it is locked, use the usermod command. For
example, to set the inactivity period to 30 days:
# usermod -f 30 username
To change the default inactivity period for new user accounts, use the useradd command:
# useradd -D -f 30
A value of -1 specifies that user accounts are not locked due to inactivity.
For more information, see the useradd(8) and usermod(8) manual pages.
Verify that no user accounts other than root have a user ID of 0.
# awk -F":" '$3 == 0 { print $1 }' /etc/passwd
root
If you install software that creates a default user account and password, change the vendor's default
password immediately. Centralized user authentication using an LDAP implementation such as OpenLDAP
can help to simplify user authentication and management tasks, and also reduces the risk arising from
unused accounts or accounts without a password.
By default, an Oracle Linux system is configured so that you cannot log in directly as root. You must log
in as a named user before using either su or sudo to perform tasks as root. This configuration allows
system accounting to trace the original login name of any user who performs a privileged administrative
action. If you want to grant certain users authority to be able to perform specific administrative tasks via
sudo, use the visudo command to modify the /etc/sudoers file. For example, the following entry
grants the user erin the same privileges as root when using sudo, but defines a limited set of privileges
to frank so that he can run commands such as chkconfig, service, rpm, and yum:
erin
frank
ALL=(ALL)
ALL
ALL= SERVICES, SOFTWARE
24.9.11.1 Configuring User Authentication and Password Policies
The Pluggable Authentication Modules (PAM) feature allows you to enforce strong user authentication
and password policies, including rules for password complexity, length, age, expiration and the reuse of
previous passwords. You can configure PAM to block user access after too many failed login attempts,
after normal working hours, or if too many concurrent sessions are opened.
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Checking User Accounts and Privileges
PAM is highly customizable by its use of different modules with customisable parameters. For example,
the default password integrity checking module pam_cracklib.so tests password strength. The PAM
configuration file (/etc/pam.d/system-auth) contains the following default entries for testing a
password's strength:
password
password
password
requisite
sufficient
required
pam_cracklib.so try_first_pass retry=3 type=
pam_unix.so sha512 shadow nullok try_first_pass use_authtok
pam_deny.so
The line for pam_cracklib.so defines that a user gets three attempts to choose a good password.
From the module's default settings, the password length must a minimum of six characters, of which three
characters must be different from the previous password.
The line for pam_unix.so specifies that the module is not to perform password checking (pam_cracklib
will already have performed such checks), to use SHA-512 password hashing, to allow access if the
existing password is null, and to use the /etc/shadow file.
You can modify the control flags and module parameters to change the checking that is performed when a
user changes his or her password, for example:
password
password
password
required
required
required
pam_cracklib.so retry=3 minlen=8 difok=5 minclass=-1
pam_unix.so use_authtok sha512 shadow remember=5
pam_deny.so
The line for pam_cracklib.so defines that a user gets three attempts to choose a good password with
a minimum of eight characters, of which five characters must be different from the previous password, and
which must contain at least one upper case letter, one lower case letter, one numeric digit, and one nonalphanumeric character.
The line for pam_unix.so specifies that the module is not to perform password checking, to use
SHA-512 password hashing, to use the /etc/shadow file, and to save information about the previous five
passwords for each user in the /etc/security/opasswd file. As nullok is not specified, a user cannot
change his or her password if the existing password is null.
The omission of the try_first_pass keyword means that the user is always asked for their existing
password, even if he or she entered it for the same module or for a previous module in the stack.
Alternative modules are available for password checking, such as pam_passwdqc.so.
For more information, see Section 22.7, “About Pluggable Authentication Modules” and the
pam_cracklib(8), pam_deny(8), pam_passwdqc(8), and pam_unix(8) manual pages.
346
Chapter 25 OpenSSH Configuration
Table of Contents
25.1 About OpenSSH .....................................................................................................................
25.2 OpenSSH Configuration Files ..................................................................................................
25.2.1 OpenSSH User Configuration Files ...............................................................................
25.3 Configuring an OpenSSH Server .............................................................................................
25.4 Installing the OpenSSH Client Packages ..................................................................................
25.5 Using the OpenSSH Utilities ....................................................................................................
25.5.1 Using ssh to Connect to Another System ......................................................................
25.5.2 Using scp and sftp to Copy Files Between Systems .......................................................
25.5.3 Using ssh-keygen to Generate Pairs of Authentication Keys ...........................................
25.5.4 Enabling Remote System Access Without Requiring a Password ....................................
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347
348
349
349
349
350
351
352
352
This chapter describes how to configure OpenSSH to support secure communication between networked
systems.
25.1 About OpenSSH
OpenSSH is suite of network connectivity tools that provides secure communications between systems,
including:
scp
Secure file copying.
sftp
Secure File Transfer Protocol (FTP).
ssh
Secure shell to log on to or run a command on a remote system.
sshd
Daemon that supports the OpenSSH services.
ssh-keygen
Creates DSA or RSA authentication keys.
Unlike utilities such as rcp, ftp, telnet, rsh, and rlogin, the OpenSSH tools encrypt all network
packets between the client and server, including password authentication.
OpenSSH supports SSH protocol version 1 (SSH1) and version 2 (SSH2). In addition, OpenSSH provides
a secure way of using graphical applications over a network by using X11 forwarding. It also provides a
way to secure otherwise insecure TCP/IP protocols by using port forwarding.
25.2 OpenSSH Configuration Files
The following OpenSSH global configuration files are located in /etc/ssh:
moduli
Contains key-exchange information that is used to set up a secure
connection.
ssh_config
Contains default client configuration settings that can be overridden by the
settings in a user’s ~/.ssh/config file.
ssh_host_dsa_key
Contains the DSA private key for SSH2.
ssh_host_dsa_key.pub
Contains the DSA public key for SSH2.
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OpenSSH User Configuration Files
ssh_host_key
Contains the RSA private key for SSH1.
ssh_host_key.pub
Contains the RSA public key for SSH1.
ssh_host_rsa_key
Contains the RSA private key for SSH2.
ssh_host_rsa_key.pub
Contains the RSA public key for SSH2.
sshd_config
Contains configuration settings for sshd.
Other files can be configured in this directory. For details, see the sshd(8) manual page.
For more information, see the ssh_config(5), sshd(8), and sshd_config(5) manual pages.
25.2.1 OpenSSH User Configuration Files
To use the OpenSSH tools, a user must have an account on both the client and server systems. The
accounts do not need to be configured identically on each system.
User configuration files are located in the .ssh directory in a user's home directory (~/.ssh) on both the
client and server. OpenSSH creates this directory and the known_hosts file when the user first uses an
OpenSSH utility to connect to a remote system.
25.2.1.1 User Configuration Files in ~/.ssh on the Client
On the client side, the ~/.ssh/known_hosts file contains the public host keys that OpenSSH has
obtained from SSH servers. OpenSSH adds an entry for each new server to which a user connects.
In addition, the ~/.ssh directory usually contains one of the following pairs of key files:
id_dsa and id_dsa.pub
Contain a user's SSH2 DSA private and public keys.
id_rsa and id_rsa.pub
Contains a user's SSH2 RSA private and public keys. SSH2 RSA is
most commonly used key-pair type.
identity and identity.pub
Contains a user's SSH1 RSA private and public keys.
Caution
The private key file can be readable and writable by the user but must not be
accessible to other users.
The optional config file contains client configuration settings.
Caution
A config file can be readable and writable by the user but must not be accessible
to other users.
For more information, see the ssh(1) and ssh-keygen(1) manual pages.
25.2.1.2 User Configuration Files in ~/.ssh on the Server
On the server side, the ~/.ssh directory usually contains the following files:
authorized_keys
Contains your authorized public keys. The server uses the signed public key in this
file to authenticate a client.
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Configuring an OpenSSH Server
config
Contains client configuration settings. This file is optional.
Caution
A config file can be readable and writable by the user but
must not be accessible to other users.
environment
Contains definitions of environment variables. This file is optional.
rc
Contains commands that ssh executes when a user logs in, before the user’s shell
or command runs. This file is optional.
For more information, see the ssh(1) and ssh_config(5) manual pages.
25.3 Configuring an OpenSSH Server
Note
The default Oracle Linux installation includes the openssh and openssh-server
packages, but does not enable the sshd service.
To configure an OpenSSH server:
1. Install or update the openssh and openssh-server packages:
# yum install openssh openssh-server
2. Start the sshd service and configure it to start following a system reboot:
# service sshd start
# chkconfig sshd on
You can set sshd configuration options for features such as Kerberos authentication, X11 forwarding, and
port forwarding in the /etc/ssh/sshd_config file.
For more information, see the sshd(8) and sshd_config(5) manual pages.
25.4 Installing the OpenSSH Client Packages
Note
The default Oracle Linux installation includes the openssh and openssh-client
packages.
To configure an OpenSSH client, install or update the openssh and openssh-client packages:
# yum install openssh openssh-client
25.5 Using the OpenSSH Utilities
By default, each time you use the OpenSSH utilities to connect to a remote system, you must provide
your user name and password to the remote system. When you connect to an OpenSSH server for the
first time, the OpenSSH client prompts you to confirm that you are connected to the correct system. In the
following example, the ssh command is used to connect to the remote host host04:
$ ssh host04
349
Using ssh to Connect to Another System
The authenticity of host ‘host04 (192.0.2.104)’ can’t be
established.
RSA key fingerprint is 65:ad:38:b2:8a:6c:69:f4:83:dd:3f:8f:ba:b4:85:c7.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added ‘host04,192.0.2.104’ (RSA) to the
list of known hosts.
When you enter yes to accept the connection to the server, the client adds the server’s public host key to
the your ~/.ssh/known_hosts file. When you next connect to the remote server, the client compares the
key in this file to the one that the server supplies. If the keys do not match, you see a warning such as the
following:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@
WARNING: POSSIBLE DNS SPOOFING DETECTED!
@
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
The RSA host key for host has changed,
and the key for the according IP address IP_address
is unchanged. This could either mean that
DNS SPOOFING is happening or the IP address for the host
and its host key have changed at the same time.
Offending key for IP in /home/user/.ssh/known_hosts:10
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@
WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!
@
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is fingerprint
Please contact your system administrator.
Add correct host key in /home/user/.ssh/known_hosts to get rid of this message.
Offending key in /home/user/.ssh/known_hosts:53
RSA host key for host has changed and you have requested strict checking.
Host key verification failed.
Unless there is a reason for the remote server’s host key to have changed, such as an upgrade of either
the SSH software or the server, you should not try to connect to that machine until you have contacted its
administrator about the situation.
25.5.1 Using ssh to Connect to Another System
The ssh command allows you to log in to a remote system, or to execute a command on a remote system:
$ ssh [options] [user@]host [command]
host is the name of the remote OpenSSH server to which you want to connect.
For example, to log in to host04 with the same user name as on the local system, enter:
$ ssh host04
The remote system prompts you for your password on that system.
To connect as a different user, specify the user name and @ symbol before the remote host name, for
example:
$ ssh [email protected]
To execute a command on the remote system, specify the command as an argument, for example:
$ ssh [email protected] ls ~/.ssh
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Using scp and sftp to Copy Files Between Systems
ssh logs you in, executes the command, and then closes the connection.
For more information, see the ssh(1) manual page.
25.5.2 Using scp and sftp to Copy Files Between Systems
The scp command allows you to copy files or directories between systems. scp establishes a connection,
copies the files, and then closes the connection.
To upload a local file to a remote system:
$ scp [options] local_file [user@]host[:remote_file]
For example, copy testfile to your home directory on host04:
$ scp testfile host04
Copy testfile to the same directory but change its name to new_testfile:
$ scp testfile host04:new_testfile
To download a file from a remote system to the local system:
$ scp [options] [user@]host[:remote_file] local_file
The -r option allows you to recursively copy the contents of directories. For example, copy the directory
remdir and its contents from your home directory on remote host04 to your local home directory:
$ scp -r host04:~/remdir ~
The sftp command is a secure alternative to ftp for file transfer between systems. Unlike scp, sftp
allows you to browse the file system on the remote server before you copy any files.
To open an FTP connection to a remote system over SSH:
$ sftp [options] [user@]host
For example:
$ sftp host04
Connecting to host04...
[email protected] password: password
sftp>
Enter sftp commands at the sftp> prompt. For example, use put to upload the file newfile from the
local system to the remote system and ls to list it:
sftp> put newfile
Uploading newfile to /home/guest/newfile
foo
sftp> ls foo
foo
100% 1198
1.2KB/s
00:01
Enter help or ? to display a list of available commands. Enter bye, exit, or quit to close the connection
and exit sftp.
For more information, see the ssh(1) and sftp(1) manual pages.
351
Using ssh-keygen to Generate Pairs of Authentication Keys
25.5.3 Using ssh-keygen to Generate Pairs of Authentication Keys
The ssh-keygen command generate a public and private authentication key pair. Such authentication
keys allow you to connect to a remote system without needing to supply a password each time that you
connect. Each user must generate their own pair of keys. If root generates key pairs, only root can use
those keys.
To create a public and private SSH2 RSA key pair:
$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/guest/.ssh/id_rsa): <Enter>
Created directory '/home/guest/.ssh'.
Enter passphrase (empty for no passphrase): password
Enter same passphrase again: password
Your identification has been saved in /home/guest/.ssh/id_rsa.
Your public key has been saved in /home/guest/.ssh/id_rsa.pub.
The key fingerprint is:
5e:d2:66:f4:2c:c5:cc:07:92:97:c9:30:0b:11:90:59 [email protected]
The key's randomart image is:
+--[ RSA 2048]----+
|
.=Eo++.o
|
|
o ..B=.
|
|
o.= . |
|
o + .
|
|
S * o
|
|
. = .
|
|
.
|
|
.
|
|
|
+-----------------+
To generate an SSH1 RSA or SSH2 DSA key pair, specify the -t rsa1 or -t dsa options.
For security, in case an attacker gains access to your private key, you can specify an passphrase to
encrypt your private key. If you encrypt your private key, you must enter this passphrase each time that
you use the key. If you do not specify a passphrase, you are not prompted.
ssh-keygen generates a private key file and a public key file in ~/.ssh (unless you specify an alternate
directory for the private key file):
$ ls -l ~/.ssh
total 8
-rw-------. 1 guest guest 1743 Apr 13 12:07 id_rsa
-rw-r--r--. 1 guest guest 397 Apr 13 12:07 id_rsa.pub
For more information, see the ssh-keygen(1) manual page.
25.5.4 Enabling Remote System Access Without Requiring a Password
To be able to use the OpenSSH utilities to access a remote system without supplying a password each
time that you connect:
1. Use ssh-keygen to generate a public and private key pair, for example:
$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa): <Enter>
Created directory '/home/user/.ssh'.
Enter passphrase (empty for no passphrase): <Enter>
Enter same passphrase again: <Enter>
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Enabling Remote System Access Without Requiring a Password
...
Press Enter each time that the command prompts you to enter a passphrase.
2. Use the ssh-copy-id script to append the public key in the local ~/.ssh/id_rsa.pub file to the
~/.ssh/authorized_keys file on the remote system, for example:
$ ssh-copy-id [email protected]
[email protected]'s password: remote_password
Now try logging into the machine, with "ssh [email protected]'", and check in:
.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.
When prompted, enter your password for the remote system.
The script also changes the permissions of ~/.ssh and ~/.ssh/authorized_keys on the remote
system to disallow access by your group.
You can now use the OpenSSH utilities to access the remote system without supplying a password.
As the script suggests, you should use ssh to log into the remote system to verify that the ~/.ssh/
authorized_keys file contains only the keys for the systems from which you expect to connect. For
example:
$ ssh [email protected]
Last login: Thu Jun 13 08:33:58 2013 from local_host
host$ cat .ssh/authorized_keys
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA6OabJhWABsZ4F3mcjEPT3sxnXx1OoUcvuCiM6fg5s/ER
... FF488hBOk2ebpo38fHPPK1/rsOEKX9Kp9QWH+IfASI8q09xQ== [email protected]_host
host$ logout
Connection to host closed.
$
3. Verify that the permissions on the remote ~/.ssh directory and ~/.ssh/authorized_keys file allow
access only by you:
$ ssh [email protected] ls -al .ssh
total 4
drwx------+ 2 remote_user group
5 Jun 12 08:33 .
drwxr-xr-x+ 3 remote_user group
9 Jun 12 08:32 ..
-rw-------+ 1 remote_user group 397 Jun 12 08:33 authorized_keys
$ ssh [email protected] getfacl .ssh
# file: .ssh
# owner: remote_user
# group: group
user::rwx
group::--mask::rwx
other::--$ ssh [email protected] getfacl .ssh/authorized_keys
# file: .ssh/authorized_keys
# owner: remote_user
# group: group
user::rwgroup::--mask::rwx
other::---
If necessary, correct the permissions:
$ ssh [email protected] 'umask 077; /sbin/restorecon .ssh'
$ ssh [email protected] 'umask 077; /sbin/restorecon .ssh/authorized_keys'
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Enabling Remote System Access Without Requiring a Password
Note
If your user names are the same on the client and the server systems, you do
not need to specify your remote user name and the @ symbol.
4. If your user names are different on the client and the server systems, create a ~/.ssh/config file
with permissions 600 on the remote system that defines your local user name, for example:
$ ssh [email protected] echo -e "Host *\\\nUser local_user" '>>' .ssh/config
$ ssh [email protected] cat .ssh/config
Host *
User local_user
$ ssh [email protected] 'umask 077; /sbin/restorecon .ssh/config'
You should now be able to access the remote system without needing to specify your remote user
name, for example:
$ ssh host ls -l .ssh/config
-rw-------+ 1 remote_user group 37 Jun 12 08:34 .ssh/config
$ ssh host getfacl .ssh/config
# file: .ssh/config
# owner: remote_user
# group: group
user::rwgroup::--mask::rwx
other::---
For more information, see the ssh-copy-id(1), ssh-keygen(1), and ssh_config(5) manual pages.
354

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