in reply to
I'm an admin on a few systems that get fork-bombed accidentally a few times a semester (big computers used by students in begining OS courses). There is something you can do if you catch it while it's going on, though, as long as you do a little planning ahead. On those machines I keep about four shells nested.
set prompt="THIS IS YOUR LAST SHELL# "
(cut and paste into the terminal). Then if I notice the machine is going to Hell, I can "exec top" and "exec pkill -u person" and things like that. Although you can no longer get any new pids, you're quite free to sacrifice shells for that one last desperation command. Just a little tip, in case anyone is interested.