The IBM PC used Ctrl-Alt-Delete to launch a reboot of the computer. Linux traps this key chord and makes it available to the init system. This is done by sending the init process a SIGINT signal (although ctrlaltdel hard can undo this trap and make the key chord reboot the comptuer immediately). The init system uses /etc/inittab to determine how to handle the signal generated by the Ctrl-Alt-Delete key chord.
Most distributions cleanly reboot the system, mimicing the behaviour that most users expect. Figure 9-14 shows how this is done.
Figure 9-14. Default handling of Ctrl-Alt-Delete in /etc/inittab
# Trap CTRL-ALT-DELETE ca::ctrlaltdel:/sbin/shutdown -t3 -r now
Depending upon each individual site you may wish to disable Ctrl-Alt-Delete. This is shown in Figure 9-15.
Figure 9-15. Ignoring Ctrl-Alt-Delete in /etc/inittab
# Trap CTRL-ALT-DELETE and do nothing ca::ctrlaltdel:
Alternatively, you may wish to cleanly shut down the computer. This is very easy to explain to operators and instructions can be displayed on the monitor using /etc/issue or a Post-it Note. If the computer uses Advanced Power Management (or APM) then shutting down the computer will also remove the power.