How do I disable CTRL + ALT + DEL reboot keys shortcut on Linux server?

CTRL+ALT+DEL reboot is configured using /etc/inittab file. Edit /etc/inittab file and remove ctrlaltdel entry (login as root):
# vi /etc/inittab
Find line:
ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now
Replace it (i.e comment out the line by putting a hash mark (#) in front of it):

# ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

Close and save the file. Type command to reread /etc/inittab:
# init q