Occasionally, you’ll find a system showing symptoms of
high CPU load or one that runs out of memory for no obvious reason.
This often means an application has gone out of control on your
system. You can use ps or top to identify processes that may
be having a problem. Once you know the PID for the process, you can
use the kill command to stop the process nicely
with SIGTERM (
PID), escalating the signal
to higher strengths if necessary until the process terminates.
Occasionally you may see a process displayed by ps or top that is listed as a zombie. These are processes that are stuck while trying to terminate and are appropriately said to be in the zombie state. Just as in the cult classic film Night of the Living Dead, you can’t kill zombies, because they’re already dead!
If you have a recurring problem with zombies, there may be a bug in your system software or in an application.
Killing a process will also kill all of its child processes. For example, killing a shell will kill all the processes initiated from that shell, including other shells.