A locally logged-on user who presses Ctrl-Alt-Delete, when at the console, can reboot the system. If accidentally pressed, as could happen in the case of a mixed OS environment, this can create the risk of short-term loss of availability of systems due to unintentional reboot.
Check
Verify the Ubuntu operating system is not configured to reboot the system when Ctrl-Alt-Delete is pressed.
Check that the "ctrl-alt-del.target" (otherwise also known as reboot.target) is not active with the following command: