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

User · Answer

Pidfile contains pid of a process  It is a convention allowing long running processes to be more self-aware  Server process can inspect it to stop itself  or have heuristic that its other instance is already running  Pidfiles can also be used to conventiently kill risk manually  e g  pkill -F  lt some pid gt

User · Answer

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

User · Answer

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

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

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