You would set something up in your /etc/inittab.
This is an excerpt from doing a 'man inittab'
The process will be executed when init receives a signal from the keyboard handler that
a special key combination was pressed on the console keyboard.
The documentation for this function is not complete yet; more documentation can be found
in the kbd-x.xx packages (most recent was kbd-0.94 at the time of this writing). Basi-
cally you want to map some keyboard combination to the "KeyboardSignal" action. For
example, to map Alt-Uparrow for this purpose use the following in your keymaps file:
alt keycode 103 = KeyboardSignal
So check out the docs for kbd-0.94 and they'll tell you what to do.