In the 4BSD universe, you kill 1, and init sends SIGTERM to everything on
the system. Programs that need to clean up after themselves are expected to
catch SIGTERM and do whatever they need to do within about 15-30 seconds.
After that, init blasts the stragglers with SIGKILL, and if they still
don't die, it prints a warning on the console.

So, your "shutdown action" should be written in the code, to be run at SIGTERM.

	Erik <fair@clock.org>