Red Hat ENTERPRISE LINUX 4.5.0 - User manual

Red Hat Enterprise Linux 4.5.0
4.5.0
Reference Guide
ISBN: N/A
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Red Hat Enterprise Linux 4.5.0

Red Hat Enterprise Linux 4.5.0: Reference Guide
Copyright ©2007 Red Hat, Inc.
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Red Hat Enterprise Linux 4.5.0

Introduction ............................................................................................................ xvii
1. Changes To This Manual ............................................................................. xvii
2. Finding Appropriate Documentation .............................................................xviii
2.1. Documentation For First-Time Linux Users ........................................xviii
2.2. For the More Experienced ...................................................................xx
2.3. Documentation for Linux Gurus ...........................................................xx
3. Document Conventions ................................................................................ xxi
4. More to Come ............................................................................................. xxii
4.1. We Need Feedback! .........................................................................xxiii
I. System Reference .................................................................................................. 1
1. Boot Process, Init, and Shutdown .................................................................... 3
1. The Boot Process .................................................................................. 3
2. A Detailed Look at the Boot Process ....................................................... 3
2.1. The BIOS ................................................................................... 3
2.2. The Boot Loader ......................................................................... 4
2.3. The Kernel .................................................................................. 5
2.4. The /sbin/init Program ............................................................ 6
3. Running Additional Programs at Boot Time .............................................. 8
4. SysV Init Runlevels ................................................................................ 9
4.1. Runlevels ................................................................................... 9
4.2. Runlevel Utilities ........................................................................10
5. Shutting Down ......................................................................................11
2. The GRUB Boot Loader ................................................................................13
1. Boot Loaders and System Architecture ...................................................13
2. GRUB ..................................................................................................13
2.1. GRUB and the x86 Boot Process ................................................13
2.2. Features of GRUB ......................................................................14
3. Installing GRUB ....................................................................................15
4. GRUB Terminology ...............................................................................15
4.1. Device Names ...........................................................................16
4.2. File Names and Blocklists ...........................................................17
4.3. The Root File System and GRUB ................................................17
5. GRUB Interfaces ...................................................................................18
5.1. Interfaces Load Order .................................................................19
6. GRUB Commands ................................................................................19
7. GRUB Menu Configuration File ..............................................................21
7.1. Configuration File Structure .........................................................21
7.2. Configuration File Directives .......................................................22
8. Changing Runlevels at Boot Time ..........................................................23
9. Additional Resources ............................................................................23
9.1. Installed Documentation .............................................................24
9.2. Useful Websites .........................................................................24
9.3. Related Books ...........................................................................24
3. File System Structure ....................................................................................25
1. Why Share a Common Structure? ..........................................................25
2. Overview of File System Hierarchy Standard (FHS) ................................25
v

2.1. FHS Organization .......................................................................25
3. Special File Locations Under Red Hat Enterprise Linux ...........................30
4. The sysconfig Directory ...............................................................................31
1. Files in the /etc/sysconfig/ Directory ..................................................31
1.1. /etc/sysconfig/amd .................................................................33
1.2. /etc/sysconfig/apmd ...............................................................33
1.3. /etc/sysconfig/arpwatch ........................................................33
1.4. /etc/sysconfig/authconfig ....................................................33
1.5. /etc/sysconfig/autofs ...........................................................33
1.6. /etc/sysconfig/clock .............................................................34
1.7. /etc/sysconfig/desktop .........................................................35
1.8. /etc/sysconfig/devlabel ........................................................35
1.9. /etc/sysconfig/dhcpd .............................................................35
1.10. /etc/sysconfig/exim .............................................................36
1.11. /etc/sysconfig/firstboot ....................................................36
1.12. /etc/sysconfig/gpm ...............................................................36
1.13. /etc/sysconfig/harddisks ....................................................36
1.14. /etc/sysconfig/hwconf .........................................................37
1.15. /etc/sysconfig/i18n .............................................................37
1.16. /etc/sysconfig/init .............................................................37
1.17. /etc/sysconfig/ip6tables-config .......................................38
1.18. /etc/sysconfig/iptables-config .........................................39
1.19. /etc/sysconfig/irda .............................................................39
1.20. /etc/sysconfig/keyboard ......................................................40
1.21. /etc/sysconfig/kudzu ...........................................................40
1.22. /etc/sysconfig/mouse ...........................................................40
1.23. /etc/sysconfig/named ...........................................................41
1.24. /etc/sysconfig/netdump ........................................................42
1.25. /etc/sysconfig/network ........................................................42
1.26. /etc/sysconfig/ntpd .............................................................42
1.27. /etc/sysconfig/pcmcia .........................................................43
1.28. /etc/sysconfig/radvd ...........................................................43
1.29. /etc/sysconfig/rawdevices ..................................................43
1.30. /etc/sysconfig/samba ...........................................................43
1.31. /etc/sysconfig/selinux ........................................................44
1.32. /etc/sysconfig/sendmail ......................................................44
1.33. /etc/sysconfig/spamassassin ...............................................44
1.34. /etc/sysconfig/squid ...........................................................44
1.35. /etc/sysconfig/system-config-securitylevel ....................45
1.36. /etc/sysconfig/system-config-users ..................................45
1.37. /etc/sysconfig/system-logviewer .......................................45
1.38. /etc/sysconfig/tux ...............................................................45
1.39. /etc/sysconfig/vncservers ..................................................45
1.40. /etc/sysconfig/xinetd .........................................................46
2. Directories in the /etc/sysconfig/ Directory .........................................46
3. Additional Resources ............................................................................47
3.1. Installed Documentation .............................................................47
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5. The proc File System ....................................................................................49
1. A Virtual File System .............................................................................49
1.1. Viewing Virtual Files ...................................................................49
1.2. Changing Virtual Files ................................................................50
2. Top-level Files within the proc File System .............................................50
2.1. /proc/apm .................................................................................51
2.2. /proc/buddyinfo ......................................................................51
2.3. /proc/cmdline ..........................................................................52
2.4. /proc/cpuinfo ..........................................................................52
2.5. /proc/crypto ...........................................................................53
2.6. /proc/devices ..........................................................................53
2.7. /proc/dma .................................................................................54
2.8. /proc/execdomains ..................................................................54
2.9. /proc/fb ...................................................................................54
2.10. /proc/filesystems .................................................................54
2.11. /proc/interrupts ..................................................................55
2.12. /proc/iomem ...........................................................................55
2.13. /proc/ioports ........................................................................56
2.14. /proc/kcore ...........................................................................56
2.15. /proc/kmsg .............................................................................57
2.16. /proc/loadavg ........................................................................57
2.17. /proc/locks ...........................................................................57
2.18. /proc/mdstat ..........................................................................57
2.19. /proc/meminfo ........................................................................58
2.20. /proc/misc .............................................................................60
2.21. /proc/modules ........................................................................60
2.22. /proc/mounts ..........................................................................60
2.23. /proc/mtrr .............................................................................61
2.24. /proc/partitions ..................................................................61
2.25. /proc/pci ...............................................................................62
2.26. /proc/slabinfo ......................................................................62
2.27. /proc/stat .............................................................................64
2.28. /proc/swaps ...........................................................................64
2.29. /proc/sysrq-trigger .............................................................65
2.30. /proc/uptime ..........................................................................65
2.31. /proc/version ........................................................................65
3. Directories within /proc/ .......................................................................65
3.1. Process Directories ....................................................................65
3.2. /proc/bus/ ...............................................................................67
3.3. /proc/driver/ ..........................................................................68
3.4. /proc/fs ...................................................................................68
3.5. /proc/ide/ ...............................................................................69
3.6. /proc/irq/ ...............................................................................70
3.7. /proc/net/ ...............................................................................70
3.8. /proc/scsi/ .............................................................................71
3.9. /proc/sys/ ...............................................................................73
3.10. /proc/sysvipc/ ......................................................................85
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3.11. /proc/tty/ .............................................................................85
4. Using the sysctl Command ..................................................................86
5. Additional Resources ............................................................................87
5.1. Installed Documentation .............................................................87
5.2. Useful Websites .........................................................................87
6. Users and Groups .........................................................................................89
1. User and Group Management Tools .......................................................89
2. Standard Users .....................................................................................90
3. Standard Groups ..................................................................................91
4. User Private Groups ..............................................................................93
4.1. Group Directories .......................................................................94
5. Shadow Passwords ...............................................................................95
6. Additional Resources ............................................................................95
6.1. Installed Documentation .............................................................95
6.2. Related Books ...........................................................................96
7. The X Window System ..................................................................................99
1. The X11R6.8 Release ...........................................................................99
2. Desktop Environments and Window Managers .....................................100
2.1. Desktop Environments ..............................................................100
2.2. Window Managers ...................................................................101
3. X Server Configuration Files ................................................................101
3.1. xorg.conf ...............................................................................102
4. Fonts ..................................................................................................108
4.1. Fontconfig ................................................................................109
4.2. Core X Font System .................................................................110
5. Runlevels and X ..................................................................................112
5.1. Runlevel 3 ...............................................................................112
5.2. Runlevel 5 ...............................................................................113
6. Additional Resources ..........................................................................114
6.1. Installed Documentation ...........................................................114
6.2. Useful Websites .......................................................................114
6.3. Related Books .........................................................................115
II. Network Services Reference ................................................................................117
8. Network Interfaces ......................................................................................119
1. Network Configuration Files .................................................................119
2. Interface Configuration Files ................................................................120
2.1. Ethernet Interfaces ...................................................................120
2.2. IPsec Interfaces .......................................................................122
2.3. Channel Bonding Interfaces ......................................................124
2.4. Alias and Clone Files ................................................................125
2.5. Dialup Interfaces ......................................................................126
2.6. Other Interfaces .......................................................................127
3. Interface Control Scripts ......................................................................128
4. Network Function Files ........................................................................129
5. Additional Resources ..........................................................................130
5.1. Installed Documentation ...........................................................130
9. Network File System (NFS) .........................................................................131
Red Hat Enterprise Linux 4.5.0
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1. How It Works ......................................................................................131
1.1. Required Services ....................................................................132
1.2. NFS and portmap ....................................................................133
2. Starting and Stopping NFS ..................................................................134
3. NFS Server Configuration ....................................................................135
3.1. The /etc/exports Configuration File ........................................135
3.2. The exportfs Command ..........................................................138
4. NFS Client Configuration Files .............................................................139
4.1. /etc/fstab .............................................................................140
4.2. autofs ....................................................................................140
4.3. Common NFS Mount Options ...................................................142
5. Securing NFS .....................................................................................143
5.1. Host Access .............................................................................143
5.2. File Permissions .......................................................................145
6. Additional Resources ..........................................................................145
6.1. Installed Documentation ...........................................................145
6.2. Useful Websites .......................................................................146
6.3. Related Books .........................................................................146
10. Apache HTTP Server ................................................................................147
1. Apache HTTP Server 2.0 .....................................................................147
1.1. Features of Apache HTTP Server 2.0 ........................................147
1.2. Packaging Changes in Apache HTTP Server 2.0 ........................148
1.3. File System Changes in Apache HTTP Server 2.0 ......................148
2. Migrating Apache HTTP Server 1.3 Configuration Files .........................149
2.1. Global Environment Configuration .............................................150
2.2. Main Server Configuration ........................................................153
2.3. Virtual Host Configuration .........................................................155
2.4. Modules and Apache HTTP Server 2.0 ......................................155
3. After Installation ..................................................................................161
4. Starting and Stopping httpd ................................................................162
5. Configuration Directives in httpd.conf ................................................163
5.1. General Configuration Tips .......................................................163
5.2. ServerRoot .............................................................................164
5.3. PidFile ..................................................................................164
5.4. Timeout ..................................................................................164
5.5. KeepAlive ...............................................................................164
5.6. MaxKeepAliveRequests ...........................................................164
5.7. KeepAliveTimeout ..................................................................165
5.8. IfModule .................................................................................165
5.9. MPM Specific Server-Pool Directives .........................................165
5.10. Listen ..................................................................................166
5.11. Include .................................................................................167
5.12. LoadModule ...........................................................................167
5.13. ExtendedStatus ....................................................................167
5.14. IfDefine ...............................................................................167
5.15. SuexecUserGroup ..................................................................167
5.16. User ......................................................................................168
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5.17. Group ....................................................................................168
5.18. ServerAdmin .........................................................................168
5.19. ServerName ...........................................................................168
5.20. UseCanonicalName ................................................................169
5.21. DocumentRoot ........................................................................169
5.22. Directory .............................................................................169
5.23. Options .................................................................................170
5.24. AllowOverride ......................................................................170
5.25. Order ....................................................................................171
5.26. Allow ....................................................................................171
5.27. Deny ......................................................................................171
5.28. UserDir .................................................................................171
5.29. DirectoryIndex ....................................................................171
5.30. AccessFileName ....................................................................172
5.31. CacheNegotiatedDocs ...........................................................172
5.32. TypesConfig .........................................................................172
5.33. DefaultType .........................................................................172
5.34. HostnameLookups ..................................................................172
5.35. ErrorLog ...............................................................................173
5.36. LogLevel ...............................................................................173
5.37. LogFormat .............................................................................173
5.38. CustomLog .............................................................................174
5.39. ServerSignature ..................................................................174
5.40. Alias ....................................................................................174
5.41. ScriptAlias .........................................................................174
5.42. Redirect ...............................................................................174
5.43. IndexOptions ........................................................................175
5.44. AddIconByEncoding ...............................................................175
5.45. AddIconByType ......................................................................175
5.46. AddIcon .................................................................................175
5.47. DefaultIcon .........................................................................176
5.48. AddDescription ....................................................................176
5.49. ReadmeName ...........................................................................176
5.50. HeaderName ...........................................................................176
5.51. IndexIgnore .........................................................................176
5.52. AddEncoding .........................................................................176
5.53. AddLanguage .........................................................................176
5.54. LanguagePriority ................................................................176
5.55. AddType .................................................................................177
5.56. AddHandler ...........................................................................177
5.57. Action ..................................................................................177
5.58. ErrorDocument ......................................................................177
5.59. BrowserMatch ........................................................................177
5.60. Location ...............................................................................178
5.61. ProxyRequests ......................................................................178
5.62. Proxy ....................................................................................178
5.63. Cache Directives ....................................................................178
Red Hat Enterprise Linux 4.5.0
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5.64. NameVirtualHost ..................................................................179
5.65. VirtualHost .........................................................................179
5.66. Configuration Directives for SSL ..............................................180
6. Default Modules ..................................................................................180
7. Adding Modules ..................................................................................181
8. Virtual Hosts .......................................................................................182
8.1. Setting Up Virtual Hosts ............................................................182
8.2. The Secure Web Server Virtual Host .........................................183
9. Additional Resources ..........................................................................183
9.1. Useful Websites .......................................................................184
9.2. Related Books .........................................................................184
11. Email ........................................................................................................185
1. Email Protocols ...................................................................................185
1.1. Mail Transport Protocols ...........................................................185
1.2. Mail Access Protocols ..............................................................186
2. Email Program Classifications ..............................................................188
2.1. Mail Transfer Agent ..................................................................188
2.2. Mail Delivery Agent ..................................................................188
2.3. Mail User Agent .......................................................................189
3. Mail Transport Agents .........................................................................189
3.1. Sendmail .................................................................................189
3.2. Postfix .....................................................................................194
3.3. Fetchmail .................................................................................196
4. Mail Delivery Agents ...........................................................................200
4.1. Procmail Configuration .............................................................201
4.2. Procmail Recipes .....................................................................202
5. Mail User Agents ................................................................................207
5.1. Securing Communication ..........................................................208
6. Additional Resources ..........................................................................210
6.1. Installed Documentation ...........................................................210
6.2. Useful Websites .......................................................................211
6.3. Related Books .........................................................................211
12. Berkeley Internet Name Domain (BIND) .....................................................213
1. Introduction to DNS .............................................................................213
1.1. Nameserver Zones ...................................................................213
1.2. Nameserver Types ...................................................................214
1.3. BIND as a Nameserver .............................................................214
2. /etc/named.conf ...............................................................................215
2.1. Common Statement Types .......................................................215
2.2. Other Statement Types .............................................................220
2.3. Comment Tags ........................................................................222
3. Zone Files ..........................................................................................222
3.1. Zone File Directives ..................................................................222
3.2. Zone File Resource Records .....................................................223
3.3. Example Zone File ...................................................................226
3.4. Reverse Name Resolution Zone Files ........................................226
4. Using rndc .........................................................................................227
xi

4.1. Configuring /etc/named.conf ..................................................227
4.2. Configuring /etc/rndc.conf ....................................................228
4.3. Command Line Options ............................................................229
5. Advanced Features of BIND ................................................................230
5.1. DNS Protocol Enhancements ....................................................230
5.2. Multiple Views ..........................................................................230
5.3. Security ...................................................................................231
5.4. IP version 6 .............................................................................231
6. Common Mistakes to Avoid .................................................................231
7. Additional Resources ..........................................................................232
7.1. Installed Documentation ...........................................................232
7.2. Useful Websites .......................................................................233
7.3. Related Books .........................................................................233
13. Lightweight Directory Access Protocol (LDAP) ............................................235
1. Why Use LDAP? .................................................................................235
1.1. OpenLDAP Features ................................................................236
2. LDAP Terminology ..............................................................................236
3. OpenLDAP Daemons and Utilities ........................................................237
3.1. NSS, PAM, and LDAP ..............................................................239
3.2. PHP4, LDAP, and the Apache HTTP Server ..............................239
3.3. LDAP Client Applications ..........................................................240
4. OpenLDAP Configuration Files ............................................................240
5. The /etc/openldap/schema/ Directory ...............................................241
6. OpenLDAP Setup Overview .................................................................242
6.1. Editing /etc/openldap/slapd.conf .........................................242
7. Configuring a System to Authenticate Using OpenLDAP ........................244
7.1. PAM and LDAP ........................................................................245
7.2. Migrating Old Authentication Information to LDAP Format ...........245
8. Migrating Directories from Earlier Releases ..........................................246
9. Additional Resources ..........................................................................246
9.1. Installed Documentation ...........................................................246
9.2. Useful Websites .......................................................................247
9.3. Related Books .........................................................................248
14. Samba .....................................................................................................249
1. Introduction to Samba .........................................................................249
1.1. Samba Features ......................................................................249
2. Samba Daemons and Related Services ................................................250
2.1. Daemon Overview ....................................................................250
2.2. Starting and Stopping Samba ....................................................250
3. Samba Server Types and the smb.conf File .........................................252
3.1. Stand-alone Server ..................................................................252
3.2. Domain Member Server ............................................................254
3.3. Domain Controller ....................................................................256
4. Samba Security Modes .......................................................................261
4.1. User-Level Security ..................................................................261
4.2. Share-Level Security ................................................................261
4.3. Domain Security Mode (User-Level Security) .............................262
Red Hat Enterprise Linux 4.5.0
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4.4. Active Directory Security Mode (User-Level Security) .................262
4.5. Server Security Mode (User-Level Security) ...............................262
5. Samba Account Information Databases ................................................263
5.1. Backward Compatible Backends ...............................................263
5.2. New Backends .........................................................................264
6. Samba Network Browsing ....................................................................264
6.1. Workgroup Browsing ................................................................265
6.2. Domain Browsing .....................................................................266
6.3. WINS (Windows Internetworking Name Server) .........................266
7. Samba with CUPS Printing Support .....................................................267
7.1. Simple smb.conf Settings .........................................................267
8. Samba Distribution Programs ..............................................................268
8.1. findsmb ..................................................................................268
8.2. make_smbcodepage ..................................................................268
8.3. make_unicodemap ....................................................................269
8.4. net ..........................................................................................269
8.5. nmblookup ...............................................................................270
8.6. pdbedit ..................................................................................270
8.7. rpcclient ...............................................................................271
8.8. smbcacls .................................................................................271
8.9. smbclient ...............................................................................271
8.10. smbcontrol ...........................................................................271
8.11. smbgroupedit ........................................................................272
8.12. smbmount ...............................................................................272
8.13. smbpasswd .............................................................................272
8.14. smbspool ...............................................................................272
8.15. smbstatus .............................................................................272
8.16. smbtar ..................................................................................272
8.17. testparm ...............................................................................273
8.18. testprns ...............................................................................274
8.19. wbinfo ..................................................................................274
9. Additional Resources ..........................................................................274
9.1. Installed Documentation ...........................................................274
9.2. Red Hat Documentation ............................................................274
9.3. Related Books .........................................................................274
9.4. Useful Websites .......................................................................275
15. FTP ..........................................................................................................277
1. The File Transport Protocol .................................................................277
1.1. Multiple Ports, Multiple Modes ...................................................277
2. FTP Servers .......................................................................................278
2.1. vsftpd ....................................................................................278
3. Files Installed with vsftpd ...................................................................279
4. Starting and Stopping vsftpd ..............................................................280
4.1. Starting Multiple Copies of vsftpd ............................................280
5. vsftpd Configuration Options ..............................................................282
5.1. Daemon Options ......................................................................282
5.2. Log In Options and Access Controls ..........................................283
xiii

5.3. Anonymous User Options .........................................................285
5.4. Local User Options ...................................................................285
5.5. Directory Options .....................................................................287
5.6. File Transfer Options ................................................................288
5.7. Logging Options .......................................................................288
5.8. Network Options ......................................................................289
6. Additional Resources ..........................................................................292
6.1. Installed Documentation ...........................................................292
6.2. Useful Websites .......................................................................293
6.3. Related Books .........................................................................293
III. Security Reference .............................................................................................295
16. Pluggable Authentication Modules (PAM) ...................................................297
1. Advantages of PAM ............................................................................297
2. PAM Configuration Files ......................................................................297
2.1. PAM Service Files ....................................................................297
3. PAM Configuration File Format ............................................................298
3.1. Module Interface ......................................................................298
3.2. Control Flag .............................................................................299
3.3. Module Name ..........................................................................300
3.4. Module Arguments ...................................................................300
4. Sample PAM Configuration Files ..........................................................300
5. Creating PAM Modules ........................................................................303
6. PAM and Administrative Credential Caching .........................................304
6.1. Removing the Timestamp File ...................................................304
6.2. Common pam_timestamp Directives ..........................................304
7. PAM and Device Ownership ................................................................305
7.1. Device Ownership ....................................................................305
7.2. Application Access ...................................................................306
8. Additional Resources ..........................................................................306
8.1. Installed Documentation ...........................................................306
8.2. Useful Websites .......................................................................307
17. TCP Wrappers and xinetd ........................................................................309
1. TCP Wrappers ....................................................................................309
1.1. Advantages of TCP Wrappers ...................................................310
2. TCP Wrappers Configuration Files .......................................................310
2.1. Formatting Access Rules ..........................................................311
2.2. Option Fields ...........................................................................315
3. xinetd ...............................................................................................318
4. xinetd Configuration Files ..................................................................318
4.1. The /etc/xinetd.conf File .....................................................318
4.2. The /etc/xinetd.d/ Directory .................................................319
4.3. Altering xinetd Configuration Files ...........................................320
5. Additional Resources ..........................................................................324
5.1. Installed Documentation ...........................................................324
5.2. Useful Websites .......................................................................325
5.3. Related Books .........................................................................325
18. iptables ..................................................................................................327
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1. Packet Filtering ...................................................................................327
2. Differences between iptables and ipchains ......................................329
3. Options Used within iptables Commands ...........................................330
3.1. Structure of iptables Options ..................................................330
3.2. Command Options ...................................................................330
3.3. iptables Parameter Options ....................................................332
3.4. iptables Match Options ..........................................................333
3.5. Target Options .........................................................................336
3.6. Listing Options .........................................................................337
4. Saving iptables Rules .......................................................................338
5. iptables Control Scripts .....................................................................338
5.1. iptables Control Scripts Configuration File ...............................340
6. ip6tables and IPv6 ............................................................................341
7. Additional Resources ..........................................................................341
7.1. Installed Documentation ...........................................................341
7.2. Useful Websites .......................................................................341
19. Kerberos ..................................................................................................343
1. What is Kerberos? ..............................................................................343
1.1. Advantages of Kerberos ...........................................................343
1.2. Disadvantages of Kerberos .......................................................343
2. Kerberos Terminology .........................................................................344
3. How Kerberos Works ..........................................................................346
4. Kerberos and PAM ..............................................................................347
5. Configuring a Kerberos 5 Server ..........................................................348
6. Configuring a Kerberos 5 Client ...........................................................350
7. Additional Resources ..........................................................................351
7.1. Installed Documentation ...........................................................351
7.2. Useful Websites .......................................................................352
20. SSH Protocol ............................................................................................355
1. Features of SSH .................................................................................355
1.1. Why Use SSH? ........................................................................355
2. SSH Protocol Versions ........................................................................356
3. Event Sequence of an SSH Connection ................................................357
3.1. Transport Layer ........................................................................357
3.2. Authentication ..........................................................................358
3.3. Channels .................................................................................358
4. OpenSSH Configuration Files ..............................................................359
5. More Than a Secure Shell ...................................................................360
5.1. X11 Forwarding ........................................................................360
5.2. Port Forwarding .......................................................................361
6. Requiring SSH for Remote Connections ...............................................362
7. Additional Resources ..........................................................................362
7.1. Installed Documentation ...........................................................362
7.2. Useful Websites .......................................................................363
7.3. Related Books .........................................................................363
21. SELinux ....................................................................................................365
1. Introduction to SELinux .......................................................................365
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2. Files Related to SELinux .....................................................................365
2.1. The /selinux/ Pseudo-File System .........................................365
2.2. SELinux Configuration Files ......................................................366
2.3. SELinux Utilities .......................................................................368
3. Additional Resources ..........................................................................369
3.1. Installed Documentation ...........................................................369
3.2. Red Hat Documentation ............................................................369
3.3. Useful Websites .......................................................................369
IV. Appendixes .......................................................................................................371
A. General Parameters and Modules ...............................................................373
1. Kernel Module Utilities .........................................................................373
2. Persistent Module Loading ..................................................................376
3. Specifying Module Parameters ............................................................376
4. Storage parameters ............................................................................377
5. Ethernet Parameters ...........................................................................383
5.1. Using Multiple Ethernet Cards ...................................................390
5.2. The Channel Bonding Module ...................................................390
6. Additional Resources ..........................................................................394
6.1. Installed Documentation ...........................................................394
6.2. Useful Websites .......................................................................394
Index .....................................................................................................................395
Red Hat Enterprise Linux 4.5.0
xvi

Introduction
Welcome to the Red Hat Enterprise Linux Reference Guide.
The Red Hat Enterprise Linux Reference Guide contains useful information about the Red Hat
Enterprise Linux system. From fundamental concepts, such as the structure of the file system,
to the finer points of system security and authentication control, we hope you find this book to
be a valuable resource.
This guide is for you if you want to learn a bit more about how the Red Hat Enterprise Linux
system works. Topics that you can explore within this manual include the following:
• The boot process
• The file system structure
• The X Window System
• Network services
• Security tools
1. Changes To This Manual
This manual has been reorganized for clarity and updated for the latest features of Red Hat
Enterprise Linux 4.5.0. Some of the changes include:
A New Samba Chapter
The new Samba chapter explains various Samba daemons and configuration options.
Special thanks to John Terpstra for his hard work in helping to complete this chapter.
A New SELinux Chapter
The new SELinux chapter explains various SELinux files and configuration options. Special
thanks to Karsten Wade for his hard work in helping to complete this chapter.
An Updated proc File System Chapter
The proc file system chapter includes updated information in regards to the 2.6 kernel.
Special thanks to Arjan van de Ven for his hard work in helping to complete this chapter.
An Updated Network File System (NFS) Chapter
The Network File System (NFS) chapter has been revised and reorganized to include
NFSv4.
An Updated The X Window System Chapter
The X Window System chapter has been revised to include information on the X11R6.8
release developed by the X.Org team.
Before reading this guide, you should be familiar with the contents of the Red Hat Enterprise
xvii

Linux Installation Guide concerning installation issues, the Red Hat Enterprise Linux
Introduction to System Administration for basic administration concepts, the Red Hat Enterprise
Linux System Administration Guide for general customization instructions, and the Red Hat
Enterprise Linux Security Guide for security related instructions. This guide contains information
about topics for advanced users.
2. Finding Appropriate Documentation
You need documentation that is appropriate to your level of Linux expertise. Otherwise, you
might feel overwhelmed or may not find the necessary information to answer any questions. The
Red Hat Enterprise Linux Reference Guide deals with the more technical aspects and options of
a Red Hat Enterprise Linux system. This section helps you decide whether to look in this
manual for the information you need or to consider other Red Hat Enterprise Linux manuals,
including online sources, in your search.
Three different categories of people use Red Hat Enterprise Linux, and each of these
categories require different sets of documentation and informative sources. To help you figure
out where you should start, determine your own experience level:
New to Linux
This type of user has never used any Linux (or Linux-like) operating system before or has
had only limited exposure to Linux. They may or may not have experience using other
operating systems (such as Windows). Is this you? If so, skip ahead to Section 2.1,
“Documentation For First-Time Linux Users”.
Some Linux Experience
This type of user has installed and successfully used Linux (but not Red Hat Enterprise
Linux) before or may have equivalent experience with other Linux-like operating systems.
Does this describe you? If so, turn to Section 2.2, “For the More Experienced”.
Experienced User
This type of user has installed and successfully used Red Hat Enterprise Linux before. If
this describes you, turn to Section 2.3, “Documentation for Linux Gurus”.
2.1. Documentation For First-Time Linux Users
For someone new to Linux, the amount of information available on any particular subject, such
as printing, starting up the system or partitioning a hard drive, can be overwhelming. It helps to
initially step back and gain a decent base of information centered around how Linux works
before tackling these kinds of advanced issues.
Your first goal should be to obtain some useful documentation. This cannot be stressed enough.
Without documentation, you only become frustrated at your inability to get a Red Hat Enterprise
Linux system working the way you want.
You should acquire the following types of Linux documentation:
Introduction
xviii

•A brief history of Linux — Many aspects of Linux are the way they are because of historical
precedent. The Linux culture is also based on past events, needs, or requirements. A basic
understanding of the history of Linux helps you figure out how to solve many potential
problems before you actually see them.
•An explanation of how Linux works — While delving into the most arcane aspects of the Linux
kernel is not necessary, it is a good idea to know something about how Linux is put together.
This is particularly important if you have been working with other operating systems, as some
of the assumptions you currently hold about how computers work may not transfer from that
operating system to Linux.
•An introductory command overview (with examples) — This is probably the most important
thing to look for in Linux documentation. The underlying design philosophy for Linux is that it
is better to use many small commands connected together in different ways than it is to have
a few large (and complex) commands that do the whole job themselves. Without examples
that illustrate this approach to doing things, you may find yourself intimidated by the sheer
number of commands available on a Red Hat Enterprise Linux system.
Keep in mind that you do not have to memorize all of the available Linux commands. Different
techniques exist to help you find the specific command you need to accomplish a task. You
only need to know the general way in which Linux functions, what you need to accomplish,
and how to access the tool that gives you the exact instructions you need to execute the
command.
The Red Hat Enterprise Linux Installation Guide and the Red Hat Enterprise Linux Step By Step
Guide are excellent references for helping you get a Red Hat Enterprise Linux system
successfully installed and initially configured. The Red Hat Enterprise Linux Introduction to
System Administration is a great place to start for those learning the basics of system
administration. Start with these books and use them to build the base of your knowledge of Red
Hat Enterprise Linux. Before long, more complicated concepts begin to make sense because
you already grasp the general ideas.
Beyond reading the Red Hat Enterprise Linux manuals, several other excellent documentation
resources are available for little or no cost:
2.1.1. Introduction to Linux Websites
•http://www.redhat.com/ — On the Red Hat website, you find links to the Linux Documentation
Project (LDP), online versions of the Red Hat Enterprise Linux manuals, FAQs (Frequently
Asked Questions), a database which can help you find a Linux Users Group near you,
technical information in the Red Hat Support Knowledge Base, and more.
•http://www.linuxheadquarters.com/ — The Linux Headquarters website features easy to
follow, step-by-step guides for a variety of Linux tasks.
2.1.2. Introduction to Linux Newsgroups
Documentation For First-Time Linux Users
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You can participate in newsgroups by watching the discussions of others attempting to solve
problems, or by actively asking or answering questions. Experienced Linux users are known to
be extremely helpful when trying to assist new users with various Linux issues — especially if
you are posing questions in the right venue. If you do not have access to a news reader
application, you can access this information via the Web at http://groups.google.com/. Dozens
of Linux-related newsgroups exist, including the following:
•linux.help [news:linux.help] — A great place to get help from fellow Linux users.
•linux.redhat [news:linux.redhat] — This newsgroup primarily covers Red Hat Enterprise
Linux-specific issues.
•linux.redhat.install [news:linux.redhat.install] — Pose installation questions to this newsgroup
or search it to see how others solved similar problems.
•linux.redhat.misc [news:linux.redhat.misc] — Questions or requests for help that do not really
fit into traditional categories go here.
•linux.redhat.rpm [news:linux.redhat.rpm] — A good place to go if you are having trouble using
RPM to accomplish particular objectives.
2.2. For the More Experienced
If you have used other Linux distributions, you probably already have a basic grasp of the most
frequently used commands. You may have installed your own Linux system, and maybe you
have even downloaded and built software you found on the Internet. After installing Linux,
however, configuration issues can be very confusing.
The Red Hat Enterprise Linux System Administration Guide is designed to help explain the
various ways a Red Hat Enterprise Linux system can be configured to meet specific objectives.
Use this manual to learn about specific configuration options and how to put them into effect.
When you are installing software that is not covered in the Red Hat Enterprise Linux System
Administration Guide, it is often helpful to see what other people in similar circumstances have
done. HOWTO documents from the Linux Documentation Project, available at
http://www.redhat.com/mirrors/LDP/HOWTO/HOWTO-INDEX/howtos.html, document particular
aspects of Linux, from low-level kernel esoteric changes to using Linux for amateur radio station
work.
If you are concerned with the finer points and specifics of the Red Hat Enterprise Linux system,
the Red Hat Enterprise Linux Reference Guide is a great resource.
If you are concerned about security issues, the Red Hat Enterprise Linux Security Guide is a
great resource — explaining in concise terms best strategies and practices for securing Red Hat
Enterprise Linux.
2.3. Documentation for Linux Gurus
Introduction
xx