You can make your computer halt or reboot using ctrl-alt-del as any user or you can restrict it so that only root or /etc/shutdown.allow users can do it.
To allow any console user to do this, make a line in /etc/inittab like this:
ca::ctrlaltdel:/sbin/shutdown -t5 -h now
-t5 makes init wait 5 seconds for processes to terminate before killing them.
-h halts the system, but does not reboot. When the system is halted, another ctrl-alt-del will reboot.
To restrict the users that can use ctrl-alt-del, make the shutdown.allow file with a username per line and add "-a" to the shutdown command. If -a is added but no shutdown.allow file exists, only root and do the ctrl-alt-del.
See:
man ctrlaltdel
man shutdown
man init
man inittab
I find this config good. When in KDE, ctrl-alt-del brings up the logout dialog box to confirm logout with alt-l. Then wait a few seconds and do another ctrl-alt-del to halt. After waiting, the system is halted and another ctrl-alt-del reboots, or you can power down. It is useful when your video system crashes
and you can't see what you are doing.
