Let me start off by saying that I am not a fan of disabling ctrl+alt+delete, especially if you do not have physical access to a server. Sometimes the old three finger salute is the best and quickest method to reboot a locked and unresponsive Operating System. Regardless of this fact, some Info Sec folks think that disabling this functionality is a good idea for security. So for their sake, I will show you how to do it.
First ssh into your server and become root and change directory to what is shown below.
[root@ip-172-31-22-45 ~]# cd /etc/init
Now copy the file below exactly as I have illustrated. You do not want to try to modify the original file as it could be overwritten by Upstart.
[root@ip-172-31-22-45 init]# cp control-alt-delete.conf control-alt-delete.override
Now modify the line below and change it to run a command that will exit with an exit code of 0.
exec /sbin/shutdown -r now “Control-Alt-Delete pressed”
Something like /bin/true will work, although I am sure that you can come up with more creative ideas.
Now try ctrl+atl+delete, nothing should happen.