title: What is a .pid file and what does it contain?
body: <p>I recently come across a file with the extension .pid and explored inside it but didn't find much. The documentation says:</p>
  
  <blockquote>
    <p>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.</p>
  </blockquote>
  
  <p>Can anyone shed more light on this, or guide me to details of what's contained in the pid file?</p>