Ubuntu – Custom keyboard shortcut for terminal command `htop` not working

In fact, you cannot use Ctrl+Alt+Del as your shortcut, because it is taken by a logout message, as I just checked:

In order to enable it, you have to go to the keyboard shortcuts you went before, and disable that shortcut or give it another key binding:

Then, you will be able to add your custom shortcut. In order for this to work for sure, you have to completely disable the other shortcut:

In order to do this, select the shortcut and press the Backspace button.

Now, you have to go to the Custom Shortcuts section and add a new shortcut, containing the following:

Name: Whatever relevant

Command: gnome-system-monitor

I did this and it works fine in Ubuntu 12.04!

For some reason there is a problem using Esc key within Custom shortcuts. Here is the same (unanswered) question: Ubuntu 16.04 escape key doesn't work in custom keyboard shortcut. I found also this question: Keyboard shortcut Shift + Ctrl + Escape does not work, where in the comments @Cas says: I have opened a bug report: #1350527.

Мy suggestion is to use another key combination, for example Ctrl+Alt+Z, and command to be executed: gnome-system-monitor.