How to Disable Ctrl+Alt+Delete Key Combination for Reboot in Ubuntu

Prevent Server from Accidental Reboot

The physical access to the keyboard can simply use the Ctrl+Alt+Delete key combination to reboot the server without having to log on. Of course, someone could simply unplug the power source, but you should still prevent the use of this key combination on a production server. This forces an attacker to take more drastic measures to reboot the server, and will prevent accidental reboots at the same time
To disable the reboot action taken by pressing the Ctrl+Alt+Delete key combination, comment out the following line in the file
#exec /sbin/shutdown -r now "Control-Alt-Delete pressed"
The above command will prevent your server from accidental Rebooting

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