mirror of https://github.com/tLDP/LDP
288 lines
16 KiB
XML
288 lines
16 KiB
XML
<sect1 id="var">
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<title>/var</title>
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<para>
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Contains variable data like system logging files, mail and printer
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spool directories, and transient and temporary files.
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Some portions of /var are not shareable between different systems. For
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instance, /var/log, /var/lock, and /var/run. Other portions may be shared,
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notably /var/mail, /var/cache/man, /var/cache/fonts, and /var/spool/news.
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Why not put it into /usr? Because there might
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be circumstances when you may want to mount /usr as read-only, e.g. if it is
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on a CD or on another computer. '/var' contains variable data, i.e.
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files and directories the system must be able to write to during operation,
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whereas /usr should only contain static data. Some directories can
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be put onto separate partitions or systems, e.g. for easier backups, due to
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network topology or security concerns. Other directories have to be on the
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root partition, because they are vital for the boot process.
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'Mountable' directories are: '/home', '/mnt',
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'/tmp', '/usr' and '/var'. Essential for booting
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are: '/bin', '/boot', '/dev', '/etc',
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'/lib', '/proc' and '/sbin'.
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</para>
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<para>
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<screen>
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If /var cannot be made a separate partition, it is often preferable to move /
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var out of the root partition and into the /usr partition. (This is sometimes
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done to reduce the size of the root partition or when space runs low in the
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root partition.) However, /var must not be linked to /usr because this makes
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separation of /usr and /var more difficult and is likely to create a naming
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conflict. Instead, link /var to /usr/var.
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Applications must generally not add directories to the top level of /var. Such
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directories should only be added if they have some system-wide implication, and
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in consultation with the FHS mailing list.
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</screen>
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</para>
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<para><variablelist><varlistentry><term>/var/backups</term><listitem><para>Directory
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containing backups of various key system files such as /etc/shadow,
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/etc/group, /etc/inetd.conf and dpkg.status. They are normally renamed to
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something like dpkg.status.0, group.bak, gshadow.bak, inetd.conf.bak,
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passwd.bak, shadow.bak</para></listitem></varlistentry>
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<varlistentry><term>/var/cache</term><listitem><para>Is
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intended for cached data from applications. Such data is locally generated
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as a result of time-consuming I/O or calculation. This data can generally be
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regenerated or be restored. Unlike /var/spool, files here can be deleted
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without data loss. This data remains valid between invocations of the
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application and rebooting of the system. The existence of a separate
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directory for cached data allows system administrators to set different disk
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and backup policies from other directories in /var.</para></listitem></varlistentry>
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<varlistentry><term>/var/cache/fonts</term><listitem><para>Locally-generated
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fonts. In particular, all of the fonts which are automatically generated by
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mktexpk must be located in appropriately-named subdirectories of /var/cache/
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fonts. </para></listitem></varlistentry>
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<varlistentry><term>/var/cache/man</term><listitem><para>A
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cache for man pages that are formatted on demand. The source for manual
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pages is usually stored in /usr/share/man/; some manual pages might come
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with a pre-formatted version, which is stored in /usr/share/man/cat* (this
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is fairly rare now). Other manual pages need to be formatted when they are
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first viewed; the formatted version is then stored in /var/man so that the
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next person to view the same page won't have to wait for it to be
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formatted (/var/catman is often cleaned in the same way temporary
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directories are cleaned).</para></listitem></varlistentry>
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<varlistentry><term>/var/cache/'package-name'</term><listitem><para>Package
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specific cache data.</para></listitem></varlistentry>
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<varlistentry><term>/var/cache/www</term><listitem><para>WWW
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proxy or cache data.</para></listitem></varlistentry>
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<varlistentry><term>/var/crash</term><listitem><para>This
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directory will eventually hold system crash dumps. Currently, system crash
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dumps are not supported under Linux. However, development is already
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complete and is awaiting unification into the Linux kernel.</para></listitem></varlistentry>
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<varlistentry><term>/var/db</term><listitem><para>Data
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bank store.</para></listitem></varlistentry>
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<varlistentry><term>/var/games</term><listitem><para>Any
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variable data relating to games in /usr is placed here. It holds variable
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data that was previously found in /usr. Static data, such as help text,
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level descriptions, and so on, remains elsewhere though, such as in
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/usr/share/games. The separation of /var/games and /var/lib as in release
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FSSTND 1.2 allows local control of backup strategies, permissions, and disk
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usage, as well as allowing inter-host sharing and reducing clutter in
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/var/lib. Additionally, /var/games is the path traditionally used by BSD.</para></listitem></varlistentry>
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<varlistentry><term>/var/lib</term><listitem><para>Holds
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dynamic data libraries/files like the rpm/dpkg database and game scores.
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Furthermore, this hierarchy holds state information pertaining to an
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application or the system. State information is data that programs modify
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while they run, and that pertains to one specific host. Users shouldn't
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ever need to modify files in /var/lib to configure a package's
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operation. State information is generally used to preserve the condition of
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an application (or a group of inter-related applications) between
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invocations and between different instances of the same application. An
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application (or a group of inter-related applications) use a subdirectory of
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/var/lib for their data. There is one subdirectory, /var/lib/misc, which is
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intended for state files that don't need a subdirectory; the other
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subdirectories should only be present if the application in question is
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included in the distribution. /var/lib/'name' is the location that
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must be used for all distribution packaging support. Different distributions
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may use different names, of course.</para></listitem></varlistentry>
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<varlistentry><term>/var/local</term><listitem><para>Variable
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data for local programs (i.e., programs that have been installed by the
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system administrator) that are installed in /usr/local (as opposed to a
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remotely mounted '/var' partition). Note that even locally installed
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programs should use the other /var directories if they are appropriate,
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e.g., /var/lock.</para></listitem></varlistentry>
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<varlistentry><term>/var/lock</term><listitem><para>Many
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programs follow a convention to create a lock file in /var/lock to indicate
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that they are using a particular device or file. This directory holds those
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lock files (for some devices) and hopefully other programs will notice the
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lock file and won't attempt to use the device or file.</para><para>Lock
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files should be stored within the /var/lock directory structure. Lock files
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for devices and other resources shared by multiple applications, such as the
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serial device lock files that were originally found in either
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/usr/spool/locks or /usr/spool/uucp, must now be stored in /var/lock. The
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naming convention which must be used is LCK.. followed by the base name of
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the device file. For example, to lock /dev/ttyS0 the file LCK..ttyS0 would
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be created. The format used for the contents of such lock files must be the
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HDB UUCP lock file format. The HDB format is to store the process identifier
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(PID) as a ten byte ASCII decimal number, with a trailing newline. For
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example, if process 1230 holds a lock file, it would contain the eleven
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characters: space, space, space, space, space, space, one, two, three, zero,
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and newline.</para></listitem></varlistentry>
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<varlistentry><term>/var/log</term><listitem><para>Log
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files from the system and various programs/services, especially login
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(/var/log/wtmp, which logs all logins and logouts into the system) and
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syslog (/var/log/messages, where all kernel and system program message are
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usually stored). Files in /var/log can often grow indefinitely, and may
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require cleaning at regular intervals. Something that is now normally
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managed via log rotation utilities such as 'logrotate'. This utility
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also allows for the automatic rotation compression, removal and mailing of
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log files. Logrotate can be set to handle a log file daily, weekly, monthly
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or when the log file gets to a certain size. Normally, logrotate runs as a
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daily cron job. This is a good place to start troubleshooting general
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technical problems.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/auth.log</term><listitem><para>Record
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of all logins and logouts by normal users and system processes.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/btmp</term><listitem><para>Log
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of all attempted bad logins to the system. Accessed via the lastb command.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/debug</term><listitem><para>Debugging
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output from various packages.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/dmesg</term><listitem><para>Kernel
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ring buffer. The content of this file is referred to by the dmesg command.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/gdm/</term><listitem><para>GDM
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log files. Normally a subset of the last X log file. See /var/log/xdm.log
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for mode details.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/kdm.log</term><listitem><para>KDM
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log file. Normally a subset of the last X log file. See /var/log/xdm.log for
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more details.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/messages</term><listitem><para>System
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logs.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/pacct</term><listitem><para>Process
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accounting is the bookkeeping of process activity. The raw data of process
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activity is maintained here. Three commands can be used to access the
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contents of this file dump-acct, sa (summary of process accounting) and
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lastcomm (list the commands executed on the system).</para></listitem></varlistentry>
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<varlistentry><term>/var/log/utmp</term><listitem><para>Active
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user sessions. This is a data file and as such it can not be viewed
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normally. A human-readable form can be created via the dump-utmp command or
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through the w, who or users commands.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/wtmp</term><listitem><para>Log
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of all users who have logged into and out of the system. The last command
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can be used to access a human readable form of this file. It also lists
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every connection and run-level change.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/xdm.log</term><listitem><para>XDM
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log file. Normally subset of the last X startup log and pretty much useless
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in light of the details the X logs is able to provide us with. Only consult
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this file if you have XDM specific issues otherwise just use the X logfile.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/XFree86.0.log,
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/var/log/XFree86.?.log</term><listitem><para>X startup logfile. An excellent
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resource for uncovering problems with X configuration. Log files are
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numbered according to when they were last used. For example, the last log
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file would be stored in /var/log/XFree86.0.log, the next
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/var/log/XFree86.9.log, so on and so forth.</para></listitem></varlistentry>
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<varlistentry><term>/var/log/syslog</term><listitem><para>The
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'system' log file. The contents of this file is managed via the
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syslogd daemon which more often than not takes care of all log manipulation
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on most systems.</para></listitem></varlistentry>
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<varlistentry><term>/var/mail</term><listitem><para>Contains
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user mailbox files. The mail files take the form
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/var/mail/'username' (Note that /var/mail may be a symbolic link to
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another directory). User mailbox files in this location are stored in the
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standard UNIX mailbox format. The reason for the location of this directory
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was to bring the FHS inline with nearly every UNIX implementation (it was
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previously located in /var/spool/mail). This change is important for
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inter-operability since a single /var/mail is often shared between multiple
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hosts and multiple UNIX implementations (despite NFS locking issues).</para></listitem></varlistentry>
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<varlistentry><term>/var/opt</term><listitem><para>Variable
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data of the program packages in /opt must be installed in
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/var/opt/'package-name', where 'package-name' is the name of
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the subtree in /opt where the static data from an add-on software package is
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stored, except where superceded by another file in /etc. No structure is
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imposed on the internal arrangement of /var/opt/'package-name'.</para></listitem></varlistentry>
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<varlistentry><term>/var/run</term><listitem><para>Contains
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the process identification files (PIDs) of system services and other
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information about the system that is valid until the system is next booted.
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For example, /var/run/utmp contains information about users currently logged
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in.</para></listitem></varlistentry>
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<varlistentry><term>/var/spool</term><listitem><para>Holds
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spool files, for instance for mail, news, and printing (lpd) and other
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queued work. Spool files store data to be processed after the job currently
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occupying a device is finished or the appropriate cron job is started. Each
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different spool has its own subdirectory below /var/spool, e.g., the cron
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tables are stored in /var/spool/cron/crontabs.</para></listitem></varlistentry>
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<varlistentry><term>/var/tmp</term><listitem><para>Temporary
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files that are large or that need to exist for a longer time than what is
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allowed for /tmp. (Although the system administrator might not allow very
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old files in /var/tmp either.)</para></listitem></varlistentry>
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<varlistentry><term>/var/named</term><listitem><para>Database
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for BIND. The Berkeley Internet Name Domain (BIND) implements an Internet
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domain name server. BIND is the most widely used name server software on the
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Internet, and is supported by the Internet Software Consortium, www.isc.org.</para></listitem></varlistentry>
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<varlistentry><term>/var/yp</term><listitem><para>Database
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for NIS (Network Information Services). NIS is mostly used to let several
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machines in a network share the same account information (eg. /etc/passwd).
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NIS was formerly called Yellow Pages (YP).</para></listitem></varlistentry></variablelist></para>
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<para>The following directories, or symbolic links to directories, are
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required in /var for FSSTND compliance:</para>
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<para><screen>
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/var/cache Application cache data
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/var/lib Variable state information
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/var/local Variable data for /usr/local
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/var/lock Lock files
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/var/log Log files and directories
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/var/opt Variable data for /opt
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/var/run Data relevant to running processes
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/var/spool Application spool data
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/var/tmp Temporary files preserved between system reboots
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</screen></para>
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<para>Several directories are 'reserved' in the sense that they must
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not be used arbitrarily by some new application, since they would conflict
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with historical and/or local practice. They are:</para>
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<para><screen>
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/var/backups
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/var/cron
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/var/msgs
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/var/preserve
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</screen></para>
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<para>The following directories, or symbolic links to directories, must be in /var,
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if the corresponding subsystem is installed:</para>
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<para><screen>
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account Process accounting logs (optional)
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crash System crash dumps (optional)
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games Variable game data (optional)
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mail User mailbox files (optional)
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yp Network Information Service (NIS) database files (optional)
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</screen></para>
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</sect1>
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