Ctrl+Alt+Backspace

In Linux, the Ctrl+Alt+Backspace key combination is used to terminate the X server, which can be useful for troubleshooting or restarting graphical sessions.

On a Linux Mint system with the Cinnamon desktop this key combination results in all of your applications being terminated and you being returned to the session login.

To disable in Linux Mint Cinnamon Desktop

correct process to disable Ctrl+Alt+Backspace in a modern Linux Mint system with Cinnamon Desktop:

1. Open the Preferences menu.
2. Select Keyboard (the graphical application).
3. Navigate to the Layouts tab.
4. Click the Options... button to open Keyboard Layout Options.
5. Locate Key sequence to kill the X server.
6. Uncheck the checkbox for Control + Alt + Backspace.
7. Click Close to save changes.

This method is indeed the standard way to disable the shortcut in Linux Mint Cinnamon, as noted in resources for Linux Mint 12 and later versions.

Linux Mint 20.1. and earlier if unchecking the box in Keyboard Layout Options fails

Enables and disable the shortcut, bypassing a known bug

gsettings set org.gnome.libgnomekbd.keyboard options "['terminate\tterminate:ctrl_alt_bksp']"
gsettings set org.gnome.libgnomekbd.keyboard options "[]"

Classic x.org method / all Linux Distributions

Edit /etc/X11/xorg.conf.d/00-keyboard.conf to include:

Section "InputClass"
    Identifier "keyboard"
    Option "XkbOptions" ""
EndSection

Or use setxkbmap -option in a startup script to ensure the shortcut is disabled.

Accidental Key Combination Activation

Ctrl+Alt+Backspace is an "arcane" shortcut that users might accidentally press, closing all graphical applications (e.g., spreadsheets, word documents, incomplete emails) and causing significant data loss.

Users are more likely to lose data from accidentally triggering this shortcut than to benefit from it to avoid a hard reset.

There are alternative ways to handle system freezes besides a hard reset (e.g., holding the power button), making Ctrl+Alt+Backspace less necessary.

User error (accidentally pressing the shortcut) is more common than a system freeze that requires Ctrl+Alt+Backspace as the only solution.

Default Disablement: In most modern Linux distributions (e.g., Ubuntu, Fedora, Debian since around 2009), Ctrl+Alt+Backspace is disabled by default in the X server configuration.

Alternatives to Hard Reset for System Freezes

• switch to Virtual Terminal (Ctrl+Alt+F1–F6):

If the system is responsive, switching to a text-based virtual terminal allows users to kill the offending process (e.g., using kill or pkill) or restart the display manager (e.g., systemctl restart gdm).

This preserves unsaved data in graphical and non-graphical applications, unlike Ctrl+Alt+Backspace or a hard reset.

Limitation: If the X server is severely hung (e.g., GPU driver crash), the system may not respond to Ctrl+Alt+F1–F6, rendering this option unavailable.

• Magic SysRq Key (REISUB):

The SysRq key sequence (e.g., Alt+SysRq+R, E, I, S, U, B) can gracefully terminate processes, sync disks, and reboot the system.

This is safer than a hard reset, as it minimizes filesystem corruption and allows some processes to shut down cleanly.

Limitation: Requires a functional kernel and keyboard driver. If the system is completely unresponsive, SysRq may not work.

• SSH from Another Machine:

If the system is networked, users can SSH in to kill processes or reboot gracefully.

Limitation: Requires network access and a running SSH server, which may not be available in a severe freeze.

History

The Ctrl+Alt+Backspace key combination, used to terminate the X server, likely emerged in the early days of the X Window System. It became a standard feature in X11 (released 1987) to provide a quick way to restart the X server. As relating to Linux the Control-Alt-Backspace keyboard combination was widely used by the mid-1990s in early distributions like Slackware (1993) and Debian (1993), which relied on the X Window System. Consider by the mid 1990s XFree86 was the dominant X Windows environment. XFree86 provided the graphical backbone for desktop environments like FVWM, CDE, and early versions of KDE (1996) and GNOME (1997). Ctrl+Alt+Backspace was a default XFree86 shortcut to restart the graphical session.

By the mid-2000s X.Org began replacing XFree86 in most distributions. Ctrl+Alt+Backspace remained a default shortcut in X.Org until around 2008–2009, when upstream X.Org and distributions like Ubuntu disabled it by default to prevent accidental data loss.

A 2013 Linux Mint forum post for Mint 15 Cinnamon noted that Ctrl+Alt+Backspace was unchecked by default in the Keyboard Layout Options for enabling the shortcut, but one user reported it still logged them out without manual enablement, suggesting inconsistencies or bugs.

A 2022 post for Linux Mint 20.1 reported a bug where disabling Ctrl+Alt+Backspace via the GUI didn’t persist after reboot, implying it could remain active despite settings.  Older posts (e.g., 2009–2014) indicate the Xorg project and Ubuntu disabled Ctrl+Alt+Backspace by default to prevent accidental data loss, but Mint sometimes diverged to keep it enabled or make enabling easier.

Linux Mint 21.1 (released December 2022, based on Ubuntu 22.04) has reverted to enabling Ctrl+Alt+Backspace by default in Cinnamon to cater to users who value its utility for resolving graphical freezes, diverging from Ubuntu’s default.