3 Easy Ways To Kill Or Terminate A Process In Linux

https://www.2daygeek.com/kill-terminate-a-process-in-linux-using-kill-pkill-killall-command

We have explained in our previous article, how to find out Process ID (PID or PPID) in Linux. Today we are going to discuss about related article that will help you to kill or terminate a hung or unresponsive program.
Basically why you want to kill a process? Most of the time the running process or program or instance will be closed without any issues while you finish the job or close the application.
In some causes if the process become hung or unresponsive then you need to kill the process manually because there is no other way to close it.
This can be done using the below three methods.

• kill Command
• pkill Command
• killall Command

Common syntax for process kill as follow.

[command] [signal] [PID]

Details :

• Command : It could be kill or pkill or killall
• Signal : SIGKILL (9) or SIGTERM (15)
• PID : Name of the process

Before experiment this, first we need to understand the signals information, which will help us to use the right signal with kill command.

Kill command offers 64 variety of signals but we are going to discuss about only two signals SIGKILL & SIGTERM out of 64, which allows user to send a terminate signal to process.
SIGKILL (9) : SIGKILL stands for Kill Signal, this will kill or terminate the process immediately, this signal cannot be caught or ignored, and thus this is a signal of last resort.
SIGTERM (15) : SIGTERM stands for termination signal, this is the best way to terminate the process but it can be caught and interpreted or ignored by the process.
To kill a process, you need to find the PID of a process. Run the any one of the below commands to get Process ID (PID) of a process.

# pidof apache2
or
# pgrep apache2
or
# pstree -p | grep "apache2"
or
# ps aux | grep "apache2"

Navigate to the following link to know more about each command.

Suggested Read : 4 Easiest Ways To Find Out Process ID (PID) In Linux

Method-1 : Using kill Command

kill allow users to terminate a process. The command kill sends the specified signal to the specified process or process group. If no signal is specified, the TERM signal is sent. The TERM signal will kill processes which do not catch this signal.
To demonstrate this, we are going to find apache2 process PID using pstree command.

# pstree -p | grep apache2
           |-apache2(29554)-+-apache2(29555)
           |                |-apache2(29556)
           |                |-apache2(29557)
           |                |-apache2(29558)
           |                `-apache2(29559)

The above output shows that the apache2 process is running in 29533 PID and we are going to terminate the process using kill command.

# kill 29554

Re-run the pstree command once again to verify whether the process is terminated or not.

# pstree -p | grep apache2

Yes, it was terminated successfully because we didn’t see any process id for apache2 process.

Method-2 : Using pkill Command

pkill stands for process kill is a command line utility which allow users to kill or terminate process in Linux through PID or process name. Make a note, pkill will kill all processes matching the process name. It allows extended regular expression patterns and other matching criteria.
To demonstrate this, we are going to check whether the desicred process MySql is running or not using pstree command.

# pstree -p | grep mysql
           |-mysqld(3861)-+-{mysqld}(3862)
           |              |-{mysqld}(3863)
           |              |-{mysqld}(3864)
           |              |-{mysqld}(3865)
           |              |-{mysqld}(3866)
           |              |-{mysqld}(3867)
           |              |-{mysqld}(3868)
           |              |-{mysqld}(3869)
           |              |-{mysqld}(3870)
           |              |-{mysqld}(3871)
           |              |-{mysqld}(3872)
           |              |-{mysqld}(3873)
           |              |-{mysqld}(3874)
           |              |-{mysqld}(3876)
           |              |-{mysqld}(3877)
           |              |-{mysqld}(3878)
           |              |-{mysqld}(3879)
           |              |-{mysqld}(3880)
           |              |-{mysqld}(3881)
           |              |-{mysqld}(3882)
           |              |-{mysqld}(3883)
           |              |-{mysqld}(3884)
           |              |-{mysqld}(3885)
           |              |-{mysqld}(3886)
           |              |-{mysqld}(3887)
           |              `-{mysqld}(5064)

The above output shows that the MySql process is running and we are going to terminate the process using pkill command.

# pkill -e mysql
mysqld killed (pid 3861)

Details :

• -e, --echo :Display what is killed

Re-run the pstree command once again to verify whether the process is terminated or not.

# pstree -p | grep mysql

Yes, it was terminated successfully because we didn’t see any process name for MySql process.
Also you can kill any user’s process using pkill command. The below output shows the list of apache2 processes, which includes parent process ID (PPID) and it’s child process ID. To test this we are going to kill apache2 process for user root, see the below output.

# ps aux | grep apache2
root       822  1.5  1.3 302680 27452 ?        Ss   15:39   0:00 /usr/sbin/apache2 -k start
www-data   823  0.0  0.4 302704  8156 ?        S    15:39   0:00 /usr/sbin/apache2 -k start
www-data   824  0.0  0.4 302704  8156 ?        S    15:39   0:00 /usr/sbin/apache2 -k start
www-data   825  0.0  0.4 302704  8156 ?        S    15:39   0:00 /usr/sbin/apache2 -k start
www-data   826  0.0  0.4 302704  8156 ?        S    15:39   0:00 /usr/sbin/apache2 -k start
www-data   827  0.0  0.4 302704  8156 ?        S    15:39   0:00 /usr/sbin/apache2 -k start
root       829  0.0  0.0  12784  1020 pts/0    S+   15:39   0:00 grep apache2

I can see, one apache2 process hold with root user, rest are binded with www-data user. We are going to kill root users apache2 process alone.

# pkill -e -u root apache2
apache2 killed (pid 822)

Yes, its killed the root user process alone.

Method-3 : Using killall Command

killall command allows user to terminate the process easily by giving process name instead of PID. It’s a good alternative to the kill command because you no need to find the PID.
To demonstrate this, we are going to check whether the desicred process fail2ban is running or not using pstree command.

# pstree -p | grep fail2ban
           |-fail2ban-server(19099)-+-{fail2ban-server}(19100)
           |                        |-{fail2ban-server}(19101)
           |                        |-{fail2ban-server}(19102)
           |                        `-{fail2ban-server}(19104)

The above output shows that the fail2ban process is running and we are going to terminate the process using killall command.

# killall -v fail2ban-server
Killed fail2ban-server(19099) with signal 15

Details :

• -v, --verbose :Report if the signal was successfully sent.

Re-run the pstree command once again to verify whether the process is terminated or not.

# pstree -p | grep fail2ban

Yes, it was terminated successfully because we didn’t see any process name for fail2ban process.
To kill particular user process.

# killall -v -u root fail2ban-server

To kill the process group.

# kill -e -g root apache2