killing zombies

[Steven Bellovin]

> If the zombie is an orphan (i.e., its parent process id is 1), you
> can always clean it up by signaling init (via kill) with SIGCLD (which
> wakes up init which then cleans up all orphaned zombies).  This has worked
> for me on SRV2 (I think, it was a while ago).

If the parent process is 1, /etc/init should find it by itself; certainly,
that happens on 4.2bsd where you don't get signal races.  But the most
common cause of processes refusing to die is when they're hung in a device
close routine -- called by exit() in the kernel.  Even if you could send
it a signal -- which you can't, since all signals are ignored by that point --
it couldn't do anything except re-enter the driver close routine.