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 conta

Answer 1

To understand pid files, refer this DOC

Some times there are certain applications that require additional support of extra plugins and utilities. So it keeps track of these utilities and plugin process running ids using this pid file for reference.

That is why whenever you restart an application all necessary plugins and dependant apps must be restarted since the pid file will become stale.