Kill a Process

kill takes a process ID as a parameter.  The process ID can be found using any of the methods described earlier in this chapter.

The following example shows the xscreensaver process (2609) which is to be terminated.

$ pgrep xscreen
2609
$ kill 2609

Though we use pgrep to find the PID of this process here we could have also used a PID from the output of top or ps.

When there a stubborn process trapping the kill command and refusing to terminate, the -9 (SIGKILL) signal should be used to kill the process. The -9 signal cannot be trapped by a process and ignored. If the xscreensaver process did not terminate after the last kill command, the new kill command would look like the following:

$ kill -9 2609

While the kill command is typically availble to all users you will only be able to kill processes you own.  To kill processes owned by other users you will need root privileges.

Kill Processes Using a Pattern

Rather than scanning through process ID (PID) numbers, it might be easier to kill a process or group of processes by searching for a pattern in the command name field.  The pkill command is one way to accomplish this, as shown below.  pkill matches processes in the same way pgrep does.  Be very careful when using pkill as you could easily kill more than you wanted to!

Here we want to kill all processes called xscreen.  First we use pgrep to make sure we get a reasonable number of PIDs back, then we kill the process with pkill.

$ pgrep xscreen
2609
$ pkill xscreen

Again, be careful using pkill, especially as root!

Kill All Processes Owned By a Particular User

The pkill command also recognizes the ?u option to look only at a specific user's processes. By adding the -u option to the pkill command, it is possible to terminate any and all processes for the specified user. If, for example, the following command was entered by user terry, all terry?s active processes would be cancelled, and terry would be kicked off the system.

$ pkill -9 ?u terry

* Please save any work in progress before trying this!

Since you have the ability to kill any user's processes this would be a quick way to stop everything they're doing.  Be careful though, doing so may not make you any friends, if you know what I mean.