The key combination Ctrl-Alt-Del will typically causes your system to reboot. If you take a look at the /etc/inittab fille, you’ll see something like this:
ca:12345:ctrlaltdel:/sbin/shutdown -r now
So if you want to prevent Ctrl-Alt-Del from rebooting your system, simply comment this line in /etc/inittab:
#ca:12345:ctrlaltdel:/sbin/shutdown -r now
or change it to something like this:
ca:12345:ctrlaltdel:/bin/echo “Ctr+Alt+Del disabled”
And then to activate the change type…
/sbin/init q
…that tells init to re-examine the /etc/inittab file.