How to Safely Force Shutdown of Mac

Question

What I want

I\'m developing a little app to force me to only work at certain times of day - I need something to force me to stop working in the even

Answer 1

The shutdown command sends running processes a signal to terminate, giving them a chance to do clean up work, if needed. So generally, when an application receives this signal (SIGTERM(inate)) it should wrap up and exit.

IIRC in Snow Leopard (10.6) Apple added something called fast-shutdown (or similar) which will send processes that have been flagged as being ok with it a SIGKILL signal, shutting them down without chance for cleanup work. This is supposed to make shutdown faster. The default is that applications still get SIGTERM and have to opt-in for SIGKILL; and they can mark themselves as "dirty", i. e. having unsaved work and do not want to be killed forcibly.

So while shutting down in the middle of a disk utility run will abort whatever disk utility is doing, IMHO it would not cause data corruption in general. However depending on the operation you are currently running, you could end up with an incomplete disk image or a half-formatted partition. Maybe you want to refrain from using it when you know the end of your configured work time is coming close.

Using cron to schedule the shutdown is a viable option if you want it to happen at a specified time. If you want it to happen after a certain amount of time after you log in, you could use the number parameter to shutdown to specify say 8 hours from now.