linux - What is a .pid file and what does it contain?

Question

I recently come across a file with the extension .pid and explored inside it but didn't find much. The documentation says:

A Pid-File is a file containing the process identification number (pid) that is stored in a well-defined location of the filesystem thus allowing other programs to find out the pid of a running script.

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 contains 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