Modifying shutdown script

I'm looking for the location of the system script that calls /sbin/shutdown. I want to change the flags so when the machine is shutdown from the finder, it halts the machine, but doesn't power off.

Alternately, I'd like to force the setting that "Start up automatically after a power failure" checks on power applied to start the machine every time the power comes on.

Is there a way to enforce a dirty shutdown wi开发者_运维知识库thout trashing the filesystem?

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In OS X, the shutdown is not done by /sbin/shutdown in a standard GUI setting.

If you want to perform something when a login or logout occurs, use login/logout hooks described here.