pidfile() writes a file containing the process ID of the program to the
/var/run directory. The file name has the form
/var/run/basename.pid. If the
basename argument is
NULL,
pidfile() will determine the program name and use that instead.
The pid file can be used as a quick reference if the process needs to be sent a signal. When the program exits, the pid file will be removed automatically, unless the program receives a fatal signal.
Note that only the first invocation of
pidfile() causes a pid file to be written; subsequent invocations have no effect unless a new
basename is supplied. If called with a new
basename,
pidfile() will remove the old pid file and write the new one.