A couple of ways depending on the situation from a terminal sudo top
then kill the process you want. Another method is to alt-F2 and put
xkill into the run box on click on the app. With the firefox hassle,
open a terminal cd to .mozilla/firefox then ls to find the name of your
actual profile folder, it will have numbers and letters, cd to it, quick
way type in the first few and hit tab, this will auto complete. Once in
the folder ls -a and look for lock and .parentlock, rm both of them then
close the terminal and try again.

The way I do it is oen a terminal window,

> ps ax | grep <process name>

where <process name> is the process or programme you want to kill

> kill -9 PID

where PID is the Process-ID of the process/programme in question (you
get this from the ps|grep command above)

oh, and ">" refers to the command line prompt

There may be a more "graphical" way of doing this, but I've never
looked for one.

on terminal, write

> sudo top

this will list the processes running. note the process-id(PID) for the
process you want to kill.
now press

> control + d

to exit to top, now write

> sudo kill <pid>

by replacing <pid> with the id you noted earlier.

Thank you very very much for the site ! I programmed something behaving
similar in FreeBASIC and one in Gambas. I will send the site to some friends,
but I will warn them it is a nasty surprise !
I opened a terminal window and gave the

xkill

command and then clicked on the moving target and it was gone. Then when I
started Firefox I chose "Start new session" instead of "Restore previous
session".

I followed these directions and manage to get rid of my problem. Thanks Alex
and everyone else for your quick replies. BTW, I'll follow the other
suggestions cause I want to learn about this, and I really didn't find that much
when I was searching.

Go to system then to administration then click on system monitor look for the
program in the list to want to stop highlight it and click the the kill process
button at the bottom of the box that should do it after that click out and go
back and try your app again if it does it again just follow the steps i just
gave you.and welcome to Ubuntu friend.

> Go to system then to administration then click on system monitor look for the
program in the list to want to stop highlight it and click the the kill process
button at the bottom of the box that should do it after that click out and go
back and try your app again if it does it again just follow the steps i just
gave you.and welcome to Ubuntu friend.
>
Before 9.04 'cntl +alt +backspace' was the way to effectively kill all and the
has been changed to 'AltG +k +sysRq' (if my memory serves me right.) I will try
it after this mail! The original report about this shows how to revert back to
CNTL +ALT +Backspace if you prefere it.

There wouldn't be any special mention of how to kill a process in ubuntu
since processes can be killed in exactly the same way as they have for
the past 40 years in unix.

In a terminal, type "kill <process id>" if you know the process id - if
you don't know the process id, you can use the "killall" command and use
the process name - e.g. "killalll firefox".

As mentioned, you can also use the top command to view and selectively
kill processes.

If you're in a gui environment, there are several types of gui process
monitors, but generally, to kill a gui app one needs only to click the
terminate button on the upper right hand corner of the window.

But if you want to see a graphical representation, you can fire up the
process monitor. In gnome for instance, this is called "system monitor"
and it's in the system administraton menu.

Right click on the top or bottom panel and select add to panel. Then look for
System Monitor and or Force Quit. That should help you out.