[HowTo] Dealing with unresponsive applications or desktops

[Hallvor]

Skill level: Beginner
Tested on: Debian Bullseye

Unresponsive applications or even unresponsive desktop environments are not common in Debian, but it can happen. Here is how you can deal with them without holding the power button for a hard shutdown. This howto was tested on Debian Bullseye, but should also work on later versions.


Unresponsive applications

Some applications can't be closed normally from the GUI. Here are a few ways to deal with that:

Method 1: Force quit from the GUI.

Open KSysGuard, Task Manager or an equivalent.
Find the unresponsive application in the list of running processes.
Right click on the process.
Click "End process" or "Kill process" to quit the application.


Method 2: Use xkill

Open the Terminal by pressing Ctrl+Alt+T on your keyboard. (You can use Ctrl+Alt+Esc in KDE or Alt+F2 and enter the command in KRunner.)
Type the command xkill and press Enter
Your cursor will now turn into an X or skull and crossbones.
Click on the unresponsive application window to force quit.


Method 3: Use the Terminal (option 1)

Open the Terminal by pressing Ctrl+Alt+T on your keyboard.
Type the command

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ps aux | grep nameoftheapplication

to find the process ID (PID) of the misbehaving application. (Replace nameoftheapplication with the actual name of the application, for instance firefox.)
Note the process ID of the unresponsive application.
Type the command

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kill PID

. Press Enter. (Replace PID with the actual process ID number you just noted.)

Method 4: Use the Terminal (option 2)
Open the Terminal by pressing Ctrl+Alt+T on your keyboard.
Type the command

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killall nameoftheapplication

, for instance

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killall firefox

.


Unresponsive desktop environment


Method 1: Get to a virtual console

Press Ctrl+Alt+F2 (or any function key between F2 to F6) to get to a virtual console.

If you are able to get to a virtual console, you can log in as root or use the following command with sudo to restart the x server.

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systemctl restart display-manager

Method 2: Restart the X server (if the keyboard shortcut is enabled)

Note: This will not work unless you have enabled the shortcut.
Press Ctrl+Alt+Backspace to restart X and get back to the login screen.


Method 3: Safely restart your computer with REISUB

I use this method only as a last resort when everything else has failed.
Press and hold down the Alt and SysRq (or Print Screen) keys on your keyboard.
While holding down the Alt and SysRq keys, type the following keys (slowly) in sequence:
R: Switch the keyboard from raw mode
E: Send the SIGTERM signal
I: Send the SIGKILL signal
S: Sync all mounted filesystems
U: Remount all filesystems in read-only mode
B: Reboot the system

Your system should now shut down and reboot normally.

If you have a hard time remembering the sequence, think of this sentence: Raising Elephants Is So Utterly Boring, or as I prefer: Reading Every Inch Stimulates Understanding Better.


Edits:
16.04.23: Fixed typo and added KDE Plasma shortcut for xkill. Thanks to sunrat.

[kent_dorfman766]

IMHO, xkill should be a menu option on anyone's pulldown menus. Highly useful but not well known.

[sunrat]

xkill shortcut is Ctrl-Alt-Esc here on Bullseye Plasma. It turns the cursor into a skull and crossbones.

[FreewheelinFrank]

Wayland has a "check-alive" feature that will ping an app to ask for a response (pong) to say if it is busy with a task. If Wayland gets no response, it assumes the app has frozen and calls it irresponsive. Some apps as yet fail to return this "busy" pong. At least this was true for me some time ago.

If apps in Gnome on Wayland produce a pop-up saying they may be unresponsive, but are actually just working on a task, it is possible to edit the check-alive-timeout period to a longer period. Default is 5 seconds, which could be too short.

Details here.