This directory was once intended for system information data
describing the system since it was booted. These functions have been
moved to /run; this directory exists to ensure
compatibility with systems and software using an older version of this
specification.
In general, the requirements for /run shall
also apply to /var/run. It is valid to implement
/var/run as a symlink to
/run.
The utmp file, which stores information
about who is currently using the system, is located in this
directory.
Programs should not access both /var/run
and /run directly, except to access
/var/run/utmp.
[45]
[45] This is to prevent confusion about where transient files are
located. In general, a program should use either
/var/run or /run to access
these files, not both.