How to use Kill, Pkill and Killall to Terminate a Process in Linux

To use Kill, Pkill and Killall Commands to Terminate a Process in Linux

Linux Operating System provides Kill command to terminate a process, which makes it possible to continue running the server without the necessity of reboot after making a major change or update. The kill command can be executed directly or from a shell script in a number of ways. Using kill command from /usr/bin will supply you additional feature to kill a process by process name. Kill, Pkill and Killall Commands to Terminate a Process in Linux are explained in this tutorial.

List of Signal Name for a kill command

SIGTERM is the safest and default way to kill a process. SIGHUP is not a secure way of killing a process as SIGTERM. SIGKILL is the most dangerous way to kill a process that terminates a process without saving.

To kill a process, it is necessary to know the Process ID of a process. Whenever a program begins, automatically an unique PID is created for that process. Run the following command to know all the processes and their assigned pid.

[root@linuxhelp ~]# ps -A
  PID TTY          TIME CMD
    1 ?        00:00:01 init
    2 ?        00:00:00 kthreadd
    3 ?        00:00:00 migration/0
    4 ?        00:00:00 ksoftirqd/0
.
.
.
3913 ?        00:00:00 gnome-pty-helpe
 3914 pts/0    00:00:00 bash
 4632 ?        00:00:00 sleep
 4636 pts/0    00:00:00 ps

To customize the above output

[root@linuxhelp ~]# pidof sleep
3723

or use the following command.

[root@linuxhelp ~]# ps aux | grep sleep
root      3736  0.0  0.0 107892   624 ?        S    20:59   0:00 sleep 60
root      3744  0.0  0.0 112644   956 pts/0    R+   21:00   0:00 grep  --color=auto sleep

To execute a kill command, some important points to be noticed are:

• A user can kill all the processes.
• A root user can kill system-level-process and the process of any user.
• A user cannot kill processes which the System is using.
• A user cannot kill another user’ s process.

Execute ‘ pgrep‘ command to perform the same function is to .

[root@linuxhelp ~]# pgrep cups
3216

Use the kill command, to kill the above process ID

[root@linuxhelp ~]# kill -9 3216

The above command will kill the process with pid=3216, where PID is a Numerical Value of process. Or use the following command to do the same.

[root@linuxhelp1 Desktop]# pidof cupsd
3875
[root@linuxhelp1 Desktop]# kill -SIGTERM 3875

Killing a process using process name

[root@linuxhelp ~]# pkill nautilus

Be aware of process name before killing.

To Kill more than one process at a time

# kill PID1 PID2 PID3
or
# kill -9 PID1 PID2 PID3
or
# kill -SIGKILL PID1 PID2 PID3

To kill a process that has too many instances and a number of child processes, then use ‘ killall‘ .

Use the below command, to kill all ssh-agent instances with child processes.

[root@linuxhelp ~]# killall ssh-agent

To check the status of the process use the below command:

[root@linuxhelp Desktop]# systemctl status ssh-agent
ssh-agent.service
   Loaded: not-found (Reason: No such file or directory)
   Active: inactive (dead)

[root@linuxhelp Desktop]# pgrep ssh-agent