Open a terminal (Konsole, Terminal, xterm, gnome-terminal, or press CTRL+ALT+F1*). Don’t type in the $ and # signs. Those indicate the beginning of a line which you have to type. *You can use any key from F1 to F6 here. Press CTRL+ALT+F7 to go back to the GUI.

Type:
$ ps -e
If you don’t see the whole list, you can scroll up and down with SHIFT+PAGE_UP and SHIFT+PAGE_DOWN.

Find the process’ number and type:
$ kill 12345
Where 12345 is the number of your process.

If it didn’t die, type:
$ kill -9 12345
Where 12345 is the process’ number.

If it still didn’t die, type:
$ su
# kill -9 12345
# exit
You can also use:
$ sudo su
instead of “$ su” if you don’t know/have the root password but you happen to be a sudo-er.

If it still didn’t die, type:
$ pstree
Now find process’ parent process (the one to the left of it), and repeat everything for the parent process.

Warning: don’t try killing “gdm”, “kdm”, “xdm” or “init” unless you really know what you’re doing.

You can also use:
$ pkill fullprocessname
instead of
$ kill processnumber
You can usually see the full process’ name in the “pstree” and “ps -e”, next to it’s number.

If you want to kill all instances of something, type:
$ killall fullprocessname

Full process name may be different from the program’s name, for example firefox’s full process name may be “firefox-bin” instead of just “firefox”.

Both pkill and killall can use -9 parameter as well. This parameter tells it to kill forcefully (and not gently). For example:
$ pkill -9 firefox-bin
$ killall -9 npviewer.bin

$ su
Password:
# ps -e|grep part-of-process-name
# kill -9 PID
# exit
$ echo continue with what you were doing

Where PID is process ID (that number). You can use ‘pstree’ instead of ‘ps -e|grep blah’ if you want.

“ls” has practically absolutely nothing to do with killing a process. It is used to list segments (usually files) in a directory.

If I want to kill firefox (No offence mozilla ;), this is what I use:

pstree -p | grep fire*

this displays:
|-firefox(28060)-+-{firefox}(28070)
| |-{firefox}(28071)
| |-{firefox}(28072)

Then I would kill it using:
kill -9 28060

Use “$ ps -ejH” to display all processes in a tree. You might want to also “$ ps -ejH>tempprocesseslist;gedit tempprocesseslist;rm tempprocesseslist” to view the files nicely. Use ‘kate’, ‘mousepad’, ‘vi’, ‘nano’ or whatever instead of ‘gedit’ if you like/need.

Btw, don’t type/copy-paste the quotes and the $ sign ^^.

Now if you’re killing a process but it jumps back, maybe try killing/debugging it’s parent instead. Parent processes are those to the left (with less spacing at the left side) in the “tree”.

Explanation:
‘$ ps -ejH’
Displays all processes in a tree. This part is almost absolutely harmless (it takes up a lot of screen space). Use shift+pageUp/pageDown to scroll through the list if you’re stuck in CTRL+ALF+F1-6.

‘$ ps -ejH>tempprocesseslist’
Outputs to a file named ‘tempprocesseslist’ instead of screen. You can use any other filename istead of ‘tempprocesseslist’, but than you must use the same one in all three commands.

‘$ ps -ejH>tempprocesseslist;gedit tempprocesseslist’

Also open the file in text editor.
‘$ ps -ejH>tempprocesseslist;gedit tempprocesseslist;rm tempprocesseslist’
Also remove the file after it is no longer needed.