Disable the ctrl + Alt + delete key combination, one need to mask a service. This is like disabling a service,
Run the following command:
[root@RHEL7 ~]# ln -sf /dev/null /etc/systemd/system/ctrl-alt-del.target
[root@RHEL7 ~]# systemctl mask ctrl-alt-del.target
Created symlink from /etc/systemd/system/ctrl-alt-del.target to /dev/null.
NOTE: systemd will recognize units symlinked to /dev/null and show them as masked. If one try to send key combination, this will fail with following similar error.
However above steps will not disable ctrl + Alt + delete key combination, in GUI mode. To disable it in GUI change keyboard settings.
Navigate to Applications -> System Tools -> Settings -> Keyboard -> Shortcuts -> System
Set value of `Logout` as Disabled