REDHAT ENTERPRISE LINUX 4.5.0 Reference Manual

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

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Red Hat Enterprise Linux 4.5.0 ...

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Red Hat Enterprise Linux 4.5.0: Reference Guide Copyright © 2007 Red Hat, Inc. Copyright © 2007 by Red Hat, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, V1.0 or later (the...

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Red Hat Enterprise Linux 4.5.0 ...

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Introduction ............................................................................................................ xvii 1. Changes To This Manual ............................................................................. xvii 2. Finding App...

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2.1. FHS Organization .......................................................................25 3. Special File Locations Under Red Hat Enterprise Linux ...........................30 4. The sysconfig Directory ...........................................

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5. The proc File System ....................................................................................49 1. A Virtual File System .............................................................................49 1.1. Viewing Virtual Files ..........

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3.11. /proc/tty/ .............................................................................85 4. Using the sysctl Command ..................................................................86 5. Additional Resources ...................................

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1. How It Works ......................................................................................131 1.1. Required Services ....................................................................132 1.2. NFS and portmap ...............................

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5.17. Group ....................................................................................168 5.18. ServerAdmin .........................................................................168 5.19. ServerName .........................................

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5.64. NameVirtualHost ..................................................................179 5.65. VirtualHost .........................................................................179 5.66. Configuration Directives for SSL ...........................

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4.1. Configuring /etc/named.conf ..................................................227 4.2. Configuring /etc/rndc.conf ....................................................228 4.3. Command Line Options ....................................................

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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 ................................................2...

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5.3. Anonymous User Options .........................................................285 5.4. Local User Options ...................................................................285 5.5. Directory Options ..............................................

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1. Packet Filtering ...................................................................................327 2. Differences between iptables and ipchains ......................................329 3. Options Used within iptables Commands ..................

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2. Files Related to SELinux .....................................................................365 2.1. The /selinux/ Pseudo-File System .........................................365 2.2. SELinux Configuration Files ....................................

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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 sys...

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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 instruct...

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• 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 ho...

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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...

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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 a long-time Red Hat Enterprise Linux user, you probably already know that on...

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Additionally, the manual uses different strategies to draw your attention to pieces of information. In order of how critical the information is to you, these items are marked as follows: Note A note is typically information that you need to understan...

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4.1. We Need Feedback! If you find an error in the Red Hat Enterprise Linux Reference Guide, or if you have thought of a way to make this manual better, we would love to hear from you! Please submit a report in Bugzilla (http://bugzilla.redhat.com/bu...

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xxiv ...

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Part I. System Reference To manage the system effectively, it is crucial to know about its components and how they fit together. This part outlines many important aspects of the system. It covers the boot process, the basic file system layout, the lo...

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...

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Boot Process, Init, and Shutdown An important and powerful aspect of Red Hat Enterprise Linux is the open, user-configurable method it uses for starting the operating system. Users are free to configure many aspects of the boot process, including spe...

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1 GRUB reads ext3 file systems as ext2, disregarding the journal file. Refer to the chapter titled The ext3 File System in the Red Hat Enterprise Linux System Administration Guide for more information on the ext3 file system. Other platforms use diff...

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Note If Symmetric Multi-Processor (SMP) kernel support is installed, more than one option is presented the first time the system is booted. In this situation GRUB displays Red Hat Enterprise Linux (<kernel-version>-smp), which is the SMP kernel...

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When the kernel is loaded, it immediately initializes and configures the computer's memory and configures the various hardware attached to the system, including all processors, I/O subsystems, and storage devices. It then looks for the compresse...

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-> ../init.d/dc_server K10psacct -> ../init.d/psacct K10radiusd -> ../init.d/radiusd K12dc_client -> ../init.d/dc_client K12FreeWnn -> ../init.d/FreeWnn K12mailman -> ../init.d/mailman K12mysqld -> ../init.d/mysqld K15httpd ->...

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2 Refer to Section 3.11, “/proc/tty/” for more information about tty devices. 3 Refer to Section 5.2, “Runlevel 5” for more information about display managers. Tip After the system is finished booting, it is possible to log in as root and exe...

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setserial commands to configure the system's serial ports. Refer to the setserial man page for more information. 4. SysV Init Runlevels The SysV init runlevel system provides a standard process for controlling which programs init launches or hal...

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In general, users operate Red Hat Enterprise Linux at runlevel 3 or runlevel 5 — both full multi-user modes. Users sometimes customize runlevels 2 and 4 to meet specific needs, since they are not used. The default runlevel for the system is listed ...

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Refer to the chapter titled Controlling Access to Services in the Red Hat Enterprise Linux System Administration Guide for more information regarding these tools. 5. Shutting Down To shut down Red Hat Enterprise Linux, the root user may issue the /sb...

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12 ...

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1 For more on the system BIOS and the MBR, refer to Section 2.1, “The BIOS”. The GRUB Boot Loader When a computer with Red Hat Enterprise Linux is turned on, the operating system is loaded into memory by a special program called a boot loader. A ...

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primary boot loader exists on less than 512 bytes of disk space within the MBR and is capable of loading either the Stage 1.5 or Stage 2 boot loader. 2. The Stage 1.5 boot loader is read into memory by the Stage 1 boot loader, if necessary. Some hard...

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• GRUB supports Logical Block Addressing (LBA) mode. LBA places the addressing conversion used to find files in the hard drive's firmware, and is used on many IDE and all SCSI hard devices. Before LBA, boot loaders could encounter the 1024-cyl...

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One of the most important things to understand before using GRUB is how the program refers to devices, such as hard drives and partitions. This information is particularly important when configuring GRUB to boot multiple operating systems. 4.1. Devic...

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• If a system has multiple drive devices, it is very important to know how the drive boot order is set in the BIOS. This is a simple task if a system has only IDE or SCSI drives, but if there is a mix of devices, it becomes critical that the type o...

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The use of the term root file system has a different meaning in regard to GRUB. It is important to remember that GRUB's root file system has nothing to do with the Linux root file system. The GRUB root file system is the top level of the specifi...

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After all changes are made, the b key executes the commands and boots the operating system. The Esc key discards any changes and reloads the standard menu interface. The c key loads the command line interface. Tip For information about changing runle...

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• boot — Boots the operating system or chain loader that was last loaded. • chainloader </path/to/file> — Loads the specified file as a chain loader. If the file is located on the first sector of the specified partition, use the blockli...

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separated list. The following is an example kernel command: kernel /vmlinuz-2.6.8-1.523 ro root=/dev/VolGroup00/LogVol00 The option in the previous example specifies that the root file system for Linux is located on the hda5 partition. • root (<...

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operating system and sets it to autoboot after 10 seconds. Two sections are given, one for each operating system entry, with commands specific to the system disk partition table. Note Note that the default is specified as an integer. This refers to t...

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• password=<password> — Prevents a user who does not know the password from editing the entries for this menu option. Optionally, it is possible to specify an alternate menu configuration file after the password=<password> directive. ...

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This chapter is only intended as an introduction to GRUB. Consult the following resources to discover more about how GRUB works. 9.1. Installed Documentation • /usr/share/doc/grub-<version-number>/ — This directory contains good information...

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File System Structure 1. Why Share a Common Structure? The file system structure is the most basic level of organization in an operating system. Almost all of the ways an operating system interacts with its users, applications, and security model are...

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The complete standard is available online at http://www.pathname.com/fhs/ [http://www.pathname.com/fhs]. 2.1.1. The /boot/ Directory The /boot/ directory contains static files required to boot the system, such as the Linux kernel. These files are ess...

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mounts. For all removeable media, use the /media/ directory. Note This directory must not be used by installation programs. 2.1.7. The /opt/ Directory The /opt/ directory provides storage for large, static application software packages. A package pla...

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arp, clock,halt, init, fsck.*, grub, ifconfig, mingetty, mkfs.*, mkswap, reboot, route, shutdown, swapoff, swapon 2.1.10. The /srv/ Directory The /srv/ directory contains site-specific data served by your system running Red Hat Enterprise Linux. This...

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The FHS says: The /usr/local hierarchy is for use by the system administrator when installing software locally. It needs to be safe from being overwritten when the system software is updated. It may be used for programs and data that are shareable am...

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3. Special File Locations Under Red Hat Enterprise Linux Red Hat Enterprise Linux extends the FHS structure slightly to accommodate special files. Most files pertaining to RPM are kept in the /var/lib/rpm/ directory. For more information on RPM, refe...

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The sysconfig Directory The /etc/sysconfig/ directory contains a variety of system configuration files for Red Hat Enterprise Linux. This chapter outlines some of the files found in the /etc/sysconfig/ directory, their function, and their contents. T...

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• keyboard • kudzu • mouse • named • netdump • network • ntpd • pcmcia • radvd • rawdevices • samba • sendmail • selinux • spamassassin • squid • system-config-securitylevel • system-config-users • system-logviewer...

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looking through the initscripts in the /etc/rc.d/ directory can prove helpful. 1.1. /etc/sysconfig/amd The /etc/sysconfig/amd file contains various parameters used by amd; these parameters allow for the automatic mounting and unmounting of file syste...

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The /etc/sysconfig/autofs file defines custom options for the automatic mounting of devices. This file controls the operation of the automount daemons, which automatically mount file systems when you use them and unmount them after a period of inacti...

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• ZONE=<filename> — The time zone file under /usr/share/zoneinfo that /etc/localtime is a copy of. The file contains information such as: ZONE="America/New York" Earlier releases of Red Hat Enterprise Linux used the following valu...

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The /etc/sysconfig/dhcpd file is used to pass arguments to the dhcpd daemon at boot time. The dhcpd daemon implements the Dynamic Host Configuration Protocol (DHCP) and the Internet Bootstrap Protocol (BOOTP). DHCP and BOOTP assign hostnames to machi...

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Warning Do not make changes to this file without careful consideration. By changing the default values, it is possible to corrupt all of the data on the hard drive(s). The /etc/sysconfig/harddisks file may contain the following: • USE_DMA=1, where ...

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The /etc/sysconfig/init file controls how the system appears and functions during the boot process. The following values may be used: • BOOTUP=<value>, where <value> is one of the following: • color — The standard color boot display...

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the /etc/sysconfig/ip6tables file by typing the following command: /sbin/service ip6tables save Once this file exists, any firewall rules saved in it persists through a system reboot or a service restart. For more information on ip6tables, refer to C...

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• DONGLE=<value>, where <value> specifies the type of dongle being used for infrared communication. This setting exists for people who use serial dongles rather than real infrared ports. A dongle is a device that is attached to a tradit...

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• FULLNAME="<value>", where "<value>" refers to the full name of the kind of mouse being used. • MOUSETYPE="<value>", where "<value>" is one of the following: • imps2 — A generic...

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configured. Type info chroot for more information. • OPTIONS="<value>", where <value> is any option listed in the man page for named except -t. In place of -t, use the ROOTDIR line above. For more information about available p...

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about what parameters are available for this file, use a Web browser to view the following file: /usr/share/doc/ntp-<version>/ntpd.htm (where <version> is the version number of ntpd). By default, this file sets the owner of the ntpd proce...

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The /etc/sysconfig/samba file is used to pass arguments to the smbd and the nmbd daemons at boot time. The smbd daemon offers file sharing connectivity for Windows clients on the network. The nmbd daemon offers NetBIOS over IP naming services. For mo...

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number installed on the system). By default, this file sets squid to start in daemon mode and sets the amount of time before it shuts itself down. 1.35. /etc/sysconfig/system-config-securitylevel The /etc/sysconfig/system-config-securitylevel file co...

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• VNCSERVERS=<value>, where <value> is set to something like "1:fred", to indicate that a VNC server should be started for user fred on display :1. User fred must have set a VNC password using the vncpasswd command before atte...

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• Various shared network function scripts which should not be edited directly. For more information on the network-scripts directory, refer to Chapter 8, Network Interfaces. • rhn/ — This directory contains the configuration files and GPG keys ...

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48 ...

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The proc File System The Linux kernel has two primary functions: to control access to physical devices on the computer and to schedule when and how processes interact with these devices. The /proc/ directory — also called the proc file system — c...

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When viewing different virtual files in the /proc/ file system, some of the information is easily understandable while some is not human-readable. This is in part why utilities exist to pull data from virtual files and display it in a useful way. Exa...

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Note In most cases, the content of the files listed in this section are not the same as those installed on your machine. This is because much of the information is specific to the hardware on which Red Hat Enterprise Linux is running for this documen...

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90 of 2^(0*PAGE_SIZE) chunks of memory. Similarly, there are 6 of 2^(1*PAGE_SIZE) chunks, and 2 of 2^(2*PAGE_SIZE) chunks of memory available. The DMA row references the first 16 MB on a system, the HighMem row references all memory greater than 4 GB...

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• cpu family — Authoritatively identifies the type of processor in the system. For an Intel-based system, place the number in front of "86" to determine the value. This is particularly helpful for those attempting to identify the archit...

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2. Character devices send data with no preconfigured size. Block devices can send and receive information in blocks of a size configured per device. For more information about devices refer to the following installed documentation: /usr/share/doc/ker...

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The first column signifies whether the file system is mounted on a block device. Those beginning with nodev are not mounted on a device. The second column lists the names of the file systems supported. The mount command cycles through the file system...

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000a0000-000bffff : Video RAM area 000c0000-000c7fff : Video ROM 000f0000-000fffff : System ROM 00100000-07ffffff : System RAM 00100000-00291ba8 : Kernel code 00291ba9-002e09cb : Kernel data e0000000-e3ffffff : VIA Technologies, Inc. VT82C597 [Apollo...

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2.15. /proc/kmsg This file is used to hold messages generated by the kernel. These messages are then picked up by other programs, such as /sbin/klogd or /bin/dmesg. 2.16. /proc/loadavg This file provides a look at the load average in regard to both t...

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This file remains in the same state as seen above unless a software RAID or md device is present. In that case, view /proc/mdstat to find the current status of mdX RAID devices. The /proc/mdstat file below shows a system with its md0 configured as a ...

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• HighTotal and HighFree — The total and free amount of memory, in kilobytes, that is not directly mapped into kernel space. The HighTotal value can vary based on the type of kernel used. • LowTotal and LowFree — The total and free amount of ...

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2.20. /proc/misc This file lists miscellaneous drivers registered on the miscellaneous major device, which is device number 10: 63 device-mapper 175 agpgart 135 rtc 134 apm_bios The first column is the minor number of each device, while the second co...

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This file provides a list of all mounts in use by the system: rootfs / rootfs rw 0 0 /proc /proc proc rw,nodiratime 0 0 none /dev ramfs rw 0 0 /dev/mapper/VolGroup00-LogVol00 / ext3 rw 0 0 none /dev ramfs rw 0 0 /proc /proc proc rw,nodiratime 0 0 /sy...

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• major — The major number of the device with this partition. The major number in the /proc/partitions, (3), corresponds with the block device ide0, in /proc/devices. • minor — The minor number of the device with this partition. This serves t...

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This file gives full information about memory usage on the slab level. Linux kernels greater than version 2.2 use slab pools to manage memory above the page level. Commonly used objects have their own slab pools. Instead of parsing the highly verbose...

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2.27. /proc/stat This file keeps track of a variety of different statistics about the system since it was last restarted. The contents of /proc/stat, which can be quite long, usually begins like the following example: cpu 259246 7001 60190 34250993 1...

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provides a snapshot of every swap file name, the type of swap space, the total size, and the amount of space in use (in kilobytes). The priority column is useful when multiple swap files are in use. The lower the priority, the more likely the swap fi...

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13 01:28 637 dr-xr-xr-x 3 rpcuser rpcuser 0 Feb 13 01:28 666 These directories are called process directories, as they are named after a program's process ID and contain information specific to that process. The owner and group of each process d...

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• stat — The status of the process. • statm — The status of the memory in use by the process. Below is a sample /proc/statm file: 263 210 210 5 0 205 0 The seven columns relate to different memory statistics for the process. From left to righ...

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example, on a standard system containing PCI and USB buses, current data on each of these buses is available within a subdirectory within /proc/bus/ by the same name, such as /proc/bus/pci/. The subdirectories and files available within /proc/bus/ va...

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/proc/fs/nfsd/exports displays the file systems being shared and the permissions granted for those file systems. For more on file system sharing with NFS, refer to Chapter 9, Network File System (NFS). 3.5. /proc/ide/ This directory contains informat...

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• capacity — The capacity of the device, in 512 byte blocks. • driver — The driver and version used to control the device. • geometry — The physical and logical geometry of the device. • media — The type of device, such as a disk. •...

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settings and statistics. This directory is primarily used with ATM networking and ADSL cards. • dev — Lists the various network devices configured on the system, complete with transmit and receive statistics. This file displays the number of byte...

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The primary file in this directory is /proc/scsi/scsi, which contains a list of every recognized SCSI device. From this listing, the type of device, as well as the model name, vendor, SCSI channel and ID data is available. For example, if a system co...

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megabytes per second, while the tape drive is only communicating at 10 megabytes per second. 3.9. /proc/sys/ The /proc/sys/ directory is different from others in /proc/ because it not only provides information about the system but also allows the sys...

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Note Any configuration changes made using the echo command disappear when the system is restarted. To make configuration changes take effect after the system is rebooted, refer to Section 4, “Using the sysctl Command”. The /proc/sys/ directory co...

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If RAID support is compiled into the kernel, a /proc/sys/dev/raid/ directory becomes available with at least two files in it: speed_limit_min and speed_limit_max. These settings determine the acceleration of RAID devices for I/O intensive tasks, such...

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space available on the file system containing the log. By default, the file looks like the following: 4 2 30 The first value dictates the percentage of free space required for logging to resume, while the second value sets the threshold percentage of...