How to Kill Processes Using Linux

Every so often a program hangs, in which case you will need a method for killing it. Linux offers several approaches for force-terminating programs from the shell.

The killall command kills all the processes by name. That means if you have three versions of the same program running, the killall command kills all three.

For example, open a small program such an image viewer. Now open another copy of the same image viewer. For this example, we've chosen Xviewer, which is a clone of Eye Of Gnome.

Now open a terminal and type in the following command:

killall xviewer

Both instances of the program will now close.

killall may produce strange results. If you have a command name which is more than 15 characters long, then the killall command will only work on the first 15 characters. If therefore you have two programs which share the same first 15 characters both programs will be canceled even though you only wanted to kill one.

To get around this you can specify the following switch which will only kill files matching the exact name.

killall -e

To make sure the killall command ignores the case of the program name that you provide use the following command:

killall -I
killall --ignore-case

When you run a command such as the following one, it creates two processes:

ps -ef | less

One command is for the ps -ef part, which lists all of the running processes on your system, and the output is piped to the less command. Both programs belong to the same group, which is bash.

To kill both programs at once, run the following command:

killall -g

For example, to kill all commands running in a bash shell run the following:

killall -g bash

To list all the running groups run the following command:

ps -g

Obviously, the killall command is quite a powerful command and you don't want to accidentally kill the wrong processes.

Using the following switch, you will be asked whether you are sure before each process is killed.

killall -i

Imagine you have been running a program and it is taking a lot longer than you hoped it would.

You can kill the command in the following way:

killall -o h4

The h in the above command stands for hours—this command kills processes running for four hours or longer.

Specify any one of the following time milestones:

• s: seconds
• m: minutes
• h: hours
• d: days
• w: weeks
• M: months
• y: years

Alternatively, to kill commands that have only just started running, use the following switch:

killall -y h4

This time the killall command will kill all programs running for less than 4 hours.

By default if you try and kill a program that isn't running you will receive the following error:

programname: no process found

If you don't want to be told if the process wasn't found use the following command:

killall -q

Instead of specifying the name of a program or command, specify a regular expression so that all processes that match the regular expression are closed by the killall command.

To use a regular expression use the following command:

killall -r <expression>

To kill a program owned by a specific user, use the -u switch:

killall -u <username> <programname>

Omit the program name to terminate all of that user's processes

By default, killall returns to the terminal when you run it but you can force killall to wait until all the processes specified have been closed before returning you to the terminal window.

Run the following command:

killall -w

If the program never dies then killall will also continue to live on.