Linux sessions, process groups, processes, threads and the ps command

I don’t want to repeat the description how sessions, process groups, processes and threads all hang together in Linux. This description is pretty clear, there are plenty of others on the net.

I keep forgetting what’s the main feature of sessions and process groups though. So here is my reminder:

  • A session can contain one or more process groups.
  • A session can optionally have a controlling tty.
  • Signals can be delivered to a process group.
  • A shell with job control puts all processes of a pipe into one process group.
  • Signals caused by the terminal (like Ctrl-C) go to all processes in the foreground process group.

The following ps command shows the relevant information from sessions down to threads.

ps -emo pid,ppid,sess,tty,pgid,tid,cls,rtprio,nice,cputime,comm,cmd

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About usrmisc

I'm a software guy and intend to write down my own miscellaneous learnings here instead of on some papers, which I don't find again. Let's see how that goes. I work mainly with Linux.
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