When a graphical program locks up on your system, it could be a hassle to kill the program.  The kill command will do it, but you need to know the Process ID of the command (sometimes apps will have many different ID’s of which all need to be killed).

A much easier way to do this would be to run xkill.  This program simply asks you to click on the window you wish to kill and you are done.

Go to a UNIX prompt and type: xkill.