PidFile

A useful piece of information about an executing process is its PID number. This is available under both Unix and Win32 in the PidFile, and this directive allows you to change its location.

PidFile file
Default file: logs/httpd.pid
Server config

By default, it is in ... /logs/httpd.pid. However, only Unix allows you to do anything easily with it; namely, to kill the process.