Is it better/preferred to kill all child processes by using PPID or PGID?

Question

I need the ability to kill all child processes running under a particular parent. What would be the better option to do this? Using PPID or PGID?

Something like this:

pkill -TERM -P

Would kill childs using a PPID. But I have read bits and pieces here and there about PGID and am curious to know if one works better over the other.

Answer 1

Killing a parent process won't kill child processes unless the parent traps and resends the signal.

Killing a process group with TERM sends the TERM signal to all members of the process group so that's the way to go, but you should make sure that the parent starts a process group (or that the parent's parent starts a process group and you don't care about the parent's parent getting possibly getting a the TERM signal if it's still alive).

If you're using a shell to start the parent (or the parent's parent), then you don't have to worry about that because each command invocation in the shell does start a process group.

(There's a Linux specific feature that may be used to tell the kernel to send children processes a signal when their parent dies, but in your standard Unix, this does not take place as far as I know. Check out prctl(2) and search for DEATHSIG if you want to learn more about it).