The /var filesystem

The Linux System Administrators' Guide
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# The `/var` filesystem

The `/var` contains data that is changed when the system is running normally. It is specific for each system, i.e., not shared over the network with other computers.

`/var/catman`

  A cache for man pages that are formatted on demand. The source for manual pages is usually stored in `/usr/man/man*`; some manual pages might come with a pre-formatted version, which is stored in `/usr/man/cat*`. Other manual pages need to be formatted when they are first viewed; the formatted version is then stored in `/var/man` so that the next person to view the same page won't have to wait for it to be formatted. (`/var/catman` is often cleaned in the same way temporary directories are cleaned.)

`/var/lib`

  Files that change while the system is running normally.

`/var/local`

  Variable data for programs that are installed in `/usr/local` (i.e., programs that have been installed by the system administrator). Note that even locally installed programs should use the other `/var` directories if they are appropriate, e.g., `/var/lock`.

`/var/lock`

  Lock files. Many programs follow a convention to create a lock file in `/var/lock` to indicate that they are using a particular device or file. Other programs will notice the lock file and won't attempt to use the device or file.

`/var/log`

  Log files from various programs, especially login (`/var/log/wtmp`, which logs all logins and logouts into the system) and syslog (`/var/log/messages`, where all kernel and system program message are usually stored). Files in `/var/log` can often grow indefinitely, and may require cleaning at regular intervals.

`/var/run`

  Files that contain information about the system that is valid until the system is next booted. For example, `/var/run/utmp` contains information about people currently logged in.

`/var/spool`

  Directories for mail, news, printer queues, and other queued work. Each different spool has its own subdirectory below `/var/spool`, e.g., the mailboxes of the users are in `/var/spool/mail`.

`/var/tmp`

  Temporary files that are large or that need to exist for a longer time than what is allowed for `/tmp`. (Although the system administrator might not allow very old files in `/var/tmp` either.)

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