TRICK: Kill a Background Process, Desktop Application on Linux

First thing you need to do is "Open The Terminal":

For example VLC Player is running in the background and we want to kill it from the terminal. The standard kill command takes a process ID number, so you’ll need to find it first.

Let's Find it by typing the following command :

# ps aux | grep vlc

 Take the process ID number from the VLC process — just to the right of the username — and provide it to the kill command. That is, run the command like so:

Now we got the Precess ID of VLC 23134, let's kill it, to kill it you need to use the following command:

# kill ####

If the Process refer to another user u need to run it as root

# sudo kill ####

replace the four  #### by the Process ID number, in our example we'll type the following command :

# kill 23134