What is a pid file and what does it contain

Question

Can anyone shed more light on this, or guide me to details of what's contained in the PID file?

Answer 1

The PID files contain the process id (a number) of a given program. For example, Apache HTTPD may write its main process number to a PID file - which is a regular text file, nothing more than that - and later use the information there contained to stop itself. You can also use that information to kill the process yourself, using cat filename.pid | xargs kill