Run a script only at shutdown (not log off or restart) on Mac OS X

Question

Is there any way to run a script only at shutdown?

I mean, only when the computer is really shutting down to off state. This script should not run when doing just a

Answer 1

It looks like the most straightforward way would be to write a small C++ application that would run as a daemon with launchctl, catch the shutdown notification but ignore the reboot notification (see below) and then call whatever is given to it as arguments, e.g. a shell script. It does not look like Apple provides libraries to catch those notifications in any other language.

From the "Kernel Programming" manual https://developer.apple.com/library/mac/documentation/Darwin/Conceptual/KernelProgramming/KernelProgramming.pdf from Apple, page 150:

"Although OS X does not have traditional BSD-style shutdown hooks, the I/O Kit provides equivalent functionality in recent versions. Since the I/O Kit provides this functionality, you must call it from C++ code."

"To register for notification, you call registerSleepWakeInterest (described in IOKit/RootDomain.h) and register for sleep notification. If the system is about to be shut down, your handler is called with the message type kIOMessageSystemWillPowerOff. If the system is about to reboot, your handler gets the message type kIOMessageSystemWillRestart. If the system is about to reboot, your handler gets the message type kIOMessageSystemWillSleep."

As you can see there is a different message for reboot, so you can handle the shutdown case exclusively.