kill, killall, pkill, xkill

1. Kill Command – Kill the process by specifying its PID

All the below kill conventions will send the TERM signal to the specified process. For the signals, either the signal name or signal number can be used. You need to lookup the pid for the process and give it as an argument to kill.

$ kill -TERM pid

$ kill -SIGTERM pid

$ kill -15 pid

Example: Kill the firefox process.

$ ps -ef | grep firefox
1986 ?        Sl     7:22 /usr/lib/firefox-3.5.3/firefox

$ kill -9 1986

2. Killall Command – Kill processes by name

Instead of specifying a process by its PID, you can specify the name of the process. If more than one process runs with that name, all of them will be killed.
Example: Kill all the firefox processes

$ killall -9 firefox

3. Pkill Command – Send signal to the process based on its name

You can send signal to any process by specifying the full name or partial name. So there is no need for you to find out the PID of the process to send the signal.

Example: Send SIGTERM to all the process which has sample in its name.

$ pkill sample

Pkill Example:

Before sending signal, you can verify which are all the process is matching the criteria using “pgrep -l”, which displays the process ID and process name of the matching processes.

In this example, all the processes are designed to log the signal to signal-log, along with its PID.

$ pgrep -l sample
12406 sample-server.p
12425 sample-server.p
12430 sample-garbagec

$ pkill -USR1 sample

$ cat signal-log
Name: ./sample-server.pl Pid: 12406 Signal Received: USR1
Name: ./sample-server.pl Pid: 12425 Signal Received: USR1
Name: ./sample-garbagecollector.pl Pid: 12430 Signal Received: USR1

Note: The part of name which you specify should be in the character within the first 15 character of the process name.

4. Xkill Command – kill a client by X resource

xkill is the simplest way to kill a malfunctioning program. When you want to kill a process, initiate xkill which will offer an cross-hair cursor. Click on the window with left cursor which will kill that process.

$ xkill
Select the window whose client you wish to kill with button 1....
xkill:  killing creator of resource 0x1200003

Note: Actually, xkill instructs XServer to terminate the client.