/var/run/directory/

[Charles R. Anderson]

On Sun, Oct 03, 2004 at 10:22:17PM -0700, Jamie Zawinski wrote:
> Maybe this is a dumb question, but what's the point of pid files,
> anyway?  Are they used by anything other than the init.d scripts?
> Why not just use /sbin/pidof instead?

pidof matches strings in /proc/*/cmdline.  The match may be imperfect
and could catch other processes (think user-created processes whose
argv[0] names are set to match a system daemon).

pidof may also return pids of child processes of the daemon.  This can
be a problem if you are trying to restart a daemon such as sshd--you
don't want to kill all open ssh connections, just restart the parent
daemon.

Using a pid file that was created by the parent daemon itself prevents
these problems, as long as you can trust who has access to write the
pid file.