From Canonical Ubuntu 16.04 Security Technical Implementation Guide
Part of SRG-OS-000480-GPOS-00227
Associated with: CCI-000366
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. In the GNOME graphical environment, risk of unintentional reboot from the Ctrl-Alt-Delete sequence is reduced because the user will be prompted before any action is taken.
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: # systemctl status ctrl-alt-del.target reboot.target - Reboot Loaded: loaded (/usr/lib/systemd/system/reboot.target; disabled) Active: inactive (dead) Docs: man:systemd.special(7) If the "ctrl-alt-del.target" is active, this is a finding.
Configure the system to disable the Ctrl-Alt-Delete sequence for the command line with the following command: # sudo systemctl mask ctrl-alt-del.target And reload the daemon to take effect # sudo systemctl daemon-reload If GNOME is active on the system, create a database to contain the system-wide setting (if it does not already exist) with the following command: # cat /etc/dconf/db/local.d/00-disable-CAD Add the setting to disable the Ctrl-Alt-Delete sequence for GNOME: [org/gnome/settings-daemon/plugins/media-keys] logout=’’
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