Have you tried pressing the key combination “Alt+Ctrl+Del” on CentOS/RHEL system? Well, Don’t try it if you don’t know what it does. The key combination “Alt+Ctrl+Del” will reboot your CentOS/RHEL server. For earlier version like CentOS/RHEL 6 the file that causes init to handle Ctrl-Alt-Del was /etc/init/control-alt-delete.conf.
In CentOS/RHEL 7, /etc/init/control-alt-delete.override no more works to override the key combination. The post provides the procedure to disable “alt+ctrl+del” key combination in order to prevent an accidental shutdown.
Masking the ctrl-alt-del.target Target
1. If requirement is to disable the “ctrl+Alt+delete” key combination, one need to mask a service. This is like disabling a service. Run the following command:
# systemctl mask ctrl-alt-del.target
# ln -sf /dev/null /etc/systemd/system/ctrl-alt-del.target
2. 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.
June 9 02:33:43 geeklab systemd: Failed to enqueue ctrl-alt-del.target job: Unit ctrl-alt-del.target is masked.
3. 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
Unmasking the ctrl-alt-del.target Target
To unmask the ctrl-alt-del.target Target and revert back, run the following command:
# systemctl unmask ctrl-alt-del.target
Disabling “ctrl-alt-del.target Target” in GUI mode, using CLI
Use the steps below to disable the “Alt+Ctrl+Del” key combination in GUI, using CLI.
Disabling per user
1. We need to check the value of “DBUS_SESSION_BUS_ADDRESS” environment variable from the already logged in GNOME. For example, a `testuser` has already logged in to the GNOME, and form the GNOME terminal, we use the following command:
$ env | grep DBUS_SESSION_BUS_ADDRESS DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-3UIRkKkjAU,guid=15771e3a5dcb3a7b2c151d00566a2dda
2. Mark down the output and then turn to the ssh session and export it:
$ export DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-3UIRkKkjAU,guid=15771e3a5dcb3a7b2c151d00566a2dda
3. Now we can use gsettings to set the value of the key:
$ gsettings set org.gnome.settings-daemon.plugins.media-keys logout ''
4. Check if the key is successfully modified:
$ gsettings get org.gnome.settings-daemon.plugins.media-keys logout ''
Disabling for all users
1. Create a file under the directory ‘/etc/dconf/db/local.d/‘ with the settings to be applied globally. For example:
# cat /etc/dconf/db/local.d/00-disable-CAD [org/gnome/settings-daemon/plugins/media-keys] logout=''
2. Update the dconf settings:
# dconf update
Verify if the ‘ctrl-alt-del’ key combination is disabled globally.
How to Disable “alt+ctrl+Del” Key Combination causing reboot in CentOS/RHEL 4,5