It’s bound to happen, one of your applications freezes up when you try to run it and you cannot close it. Instead of having to restart your system and wasting valuable time, you can simply use xkill to terminate the application so that you can continue with your computing tasks.
1. Press Alt+F2 on your keyboard.
2. When the Run Application window appears, input xkill in the textbox and click the Run button.
3. Your cursor will turn into a skull and crossbones. Move your cursor to the offending window and left click your mouse to terminate the application.