title: How to get pids in one process group in Linux OS
body: <p>I have one question on Linux pid things. How to get pids in one same group?
  It seems easy to get all pids or pgid with 'ps' command in Linux, but how to get the pids that belong to same group, or in other words, how to get the pids of one same program?
  Anyone please give me some help on this? Thank you!</p>