The /var Hierarchy
/var contains variable data files. This includes spool directories and files, administrative and logging data, and transient and temporary files.
Some portions of /var are not shareable between different systems. For instance, /var/log, /var/lock, and /var/run. Other portions may be shared, notably /var/mail, /var/cache/man, /var/cache/fonts, and /var/spool/news.
/var is specified here in order to make it possible to mount /usr read-only. Everything that once went into /usr that is written to during system operation (as opposed to installation and software maintenance) must be in /var.
If /var cannot be made a separate partition, it is often preferable to move /var out of the root partition and into the /usr partition. (This is sometimes done to reduce the size of the root partition or when space runs low in the root partition.) However, /var must not be linked to /usr because this makes separation of /usr and /var more difficult and is likely to create a naming conflict. Instead, link /var to /usr/var.
Applications must generally not add directories to the top level of /var. Such directories should only be added if they have some system-wide implication, and in consultation with the FHS mailing list.
The following directories, or symbolic links to directories, are required in /var.
Directory Description cache Application cache data lib Variable state information local Variable data for /usr/local lock Lock files log Log files and directories opt Variable data for /opt run Data relevant to running processes spool Application spool data tmp Temporary files preserved between system reboots
Several directories are `reserved' in the sense that they must not be used arbitrarily by some new application, since they would conflict with historical and/or local practice. They are:
/var/backups /var/cron /var/msgs /var/preserve
 Specific Options
The following directories, or symbolic links to directories, must be in /var, if the corresponding subsystem is installed:
Directory Description account Process accounting logs (optional) crash System crash dumps (optional) games Variable game data (optional) mail User mailbox files (optional) yp Network Information Service (NIS) database files (optional)
 /var/account : Process accounting logs (optional)
This directory holds the current active process accounting log and the composite process usage data (as used in some UNIX-like systems by lastcomm and sa).
 /var/cache : Application cache data
/var/cache is intended for cached data from applications. Such data is locally generated as a result of time-consuming I/O or calculation. The application must be able to regenerate or restore the data. Unlike /var/spool, the cached files can be deleted without data loss. The data must remain valid between invocations of the application and rebooting the system.
Files located under /var/cache may be expired in an application specific manner, by the system administrator, or both. The application must always be able to recover from manual deletion of these files (generally because of a disk space shortage). No other requirements are made on the data format of the cache directories.
The existence of a separate directory for cached data allows system administrators to set different disk and backup policies from other directories in /var.
 Specific Options
Directory Description fonts Locally-generated fonts (optional) man Locally-formatted manual pages (optional) www WWW proxy or cache data (optional) <package> Package specific cache data (optional)
 /var/cache/fonts : Locally-generated fonts (optional)
The directory /var/cache/fonts should be used to store any dynamically-created fonts. In particular, all of the fonts which are automatically generated by mktexpk must be located in appropriately-named subdirectories of /var/cache/fonts. 
 Specific Options
Other dynamically created fonts may also be placed in this tree, under appropriately-named subdirectories of /var/cache/fonts.
 /var/cache/man : Locally-formatted manual pages (optional)
This directory provides a standard location for sites that provide a read-only /usr partition, but wish to allow caching of locally-formatted man pages. Sites that mount /usr as writable (e.g., single-user installations) may choose not to use /var/cache/man and may write formatted man pages into the cat
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