To explain the meaning of a ‘Process’ in the simplest words is that it is a running instance of any application or program on your system. You may be running multiple applications simultaneously such as browsing, listening to music working on your terminal, etc. There are many background processes associated with these applications that are run by the user.
Every application or a program that runs on your system creates multiple processes associated with your single application. Sometimes this may be a problem and getting rid of these processes is the only option you have.
‘Killing’ a process is one useful option Linux provides you to stop the ongoing processes, be it a foreground process or a background process. In this article, we will review the commands like
killall to force quit any process on a system.
Why kill a Process?
Understanding the concept of killing a process is important before moving ahead in this tutorial. Killing may seem a very brutal way to express the concept, but what it figuratively means is to forcefully abort a process.
Now, why abort or quit an ongoing process? When multiple processes are running in the background, all or few of them may malfunction and can cause your system to misbehave. This delays your ongoing tasks as the malfunctioning process may freeze your system for a while.
Sometimes, quitting all the misbehaving processes seems to be the only option to restore normalcy on your system. Linux allows you to kill a process using the
pid or the process name.
Most of the Linux users are familiar with the
grep command. The
pgrep command can be used on similar lines of the
pgrep command when used, displays the
pid of the running process as specified in the command. This command will prove very helpful while using the
pgrep [options] [pattern]
Important options available with the
|list process id owned by a specific user|
|count number of matching processes|
|list only process names|
|list full path of the process name|
Let us demonstrate the use of
pgrep command using an example.
pgrep -u gaurav gnome
Here, we wish to see the
pids of the process gnome that is owned by the user ‘gaurav’. Option
-u allows you to list the
pids of the processes owned by a specific user. In this case, user gaurav.
gaurav@ubuntu:~$ pgrep -u gaurav gnome 1752 1755 1909 1922 2021 2576 4279 gaurav@ubuntu:~$
As we move ahead with this tutorial,
pgrep command will help us in confirming if the process has been killed or is still running.
Let us now move to the
pkill command and its execution.
You can use the
pkill command in Linux to kill the process using the process name. Even if you do not know the
pid of some process, even then you can kill that particular process using the
The processes can be specified with their complete name or the partial name while using the
pkill command. Even if you enter the partial name of the process, the
pkill command will match all the running processes with the matching name that you have entered in the command.
Let us display the processes currently running using the
top command. You can also use the
ps command to list the processes.
top - 14:24:02 up 3:12, 1 user, load average: 0.29, 0.48, 0.58 Tasks: 221 total, 1 running, 172 sleeping, 0 stopped, 1 zombie %Cpu(s): 5.6 us, 1.0 sy, 0.0 ni, 92.9 id, 0.4 wa, 0.0 hi, 0.1 si, 0.0 st KiB Mem : 3928240 total, 610456 free, 2233152 used, 1084632 buff/cache KiB Swap: 4083708 total, 3378884 free, 704824 used. 1187268 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 4077 gaurav 20 0 3312128 673480 118360 S 19.6 17.1 15:13.23 Web Content 3712 gaurav 20 0 3953008 453544 116476 S 4.0 11.5 9:28.39 MainThread 2010 gaurav 20 0 4084232 111096 45024 S 1.7 2.8 3:14.85 gnome-shell 1197 root 20 0 1039612 33704 22988 S 1.0 0.9 3:04.42 Xorg 1426 couchdb 20 0 3772396 16908 2520 S 0.7 0.4 1:50.83 beam.smp 3288 gaurav 20 0 722480 25048 18272 S 0.7 0.6 0:06.84 gnome-terminal- 3915 gaurav 20 0 2804900 231524 111228 S 0.7 5.9 0:54.42 Web Content 4146 gaurav 20 0 3017924 245304 120604 S 0.7 6.2 2:01.21 Web Content 4417 gaurav 20 0 2964208 234396 119160 S 0.7 6.0 0:59.90 Web Content 4860 gaurav 20 0 3066800 372920 132544 S 0.7 9.5 0:48.20 Web Content 16007 gaurav 20 0 41944 3780 3116 R 0.7 0.1 0:00.28 top
top command will display multiple processes on your terminal. Let us try to display the process with a particular name. We will use the
grep command to display a process whose name matches the string ‘mongo’.
top | grep -i mongo
Note: Here, I have used the -i option to make the search case-insensitive.
The output of this command will display the processes matching to the name ‘mongo’
1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.22 mongod 1158 mongodb 20 0 288564 4848 1320 S 1.0 0.1 1:03.25 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.27 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.29 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.31 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.33 mongod 1158 mongodb 20 0 288564 4848 1320 S 1.0 0.1 1:03.36 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.38 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.40 mongod 1158 mongodb 20 0 288564 4848 1320 S 1.0 0.1 1:03.43 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.45 mongod 1158 mongodb 20 0 288564 4848 1320 S 1.0 0.1 1:03.48 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.3 0.1 1:03.49 mongod 1158 mongodb 20 0 288564 4848 1320 S 1.0 0.1 1:03.52 mongod 1158 mongodb 20 0 288564 4848 1320 S 0.7 0.1 1:03.54 mongod 1158 mongodb 20 0 288564 4848 1320 S 1.0 0.1 1:03.57 mongod
Now, we will use the
pkill command to kill the process named ‘mongo’.
This command will now kill the process mongo. We can confirm if the process has been forced to quit by using the
pgrep command which displays the
pid of the running process according to the criteria specified by the user.
gaurav@ubuntu:~$ pgrep mongo gaurav@ubuntu:~$
This command will return no value. This confirms that the process ‘mongo’ is now killed using the
Options frequently used with
While using the
pkill command we will be needing the mentioned options for proper and effortless use of the
|match against full arguments including spaces, quotes, special characters|
|to inform the pkill process to match the process being run by the specified user|
|reloads the process|
|kills the process|
|gracefully aborts a proces|
Let us see one more example of
pkill command using the
There are two commands currently executing on the terminal as shown below.
ping bbc.com ping youtube.com
Both the processes are initiated by the
ping command. Now, suppose we wish to terminate only one process “ping youtube.com” then we have to use the
-f option with the
pkill command which kills a process with a specific name including the spaces and quotes from the process name.
gaurav@ubuntu:~$ pkill -f "ping youtube.com" gaurav@ubuntu:~$
gaurav@ubuntu:~$ ping youtube.com PING youtube.com (22.214.171.124) 56(84) bytes of data. 64 bytes from bom12s08-in-f14.1e100.net (126.96.36.199): icmp_seq=1 ttl=117 time=30.9 ms 64 bytes from bom12s08-in-f14.1e100.net (188.8.131.52): icmp_seq=2 ttl=117 time=121 ms 64 bytes from bom12s08-in-f14.1e100.net (184.108.40.206): icmp_seq=206 ttl=117 time=86.5 ms 64 bytes from bom12s08-in-f14.1e100.net (220.127.116.11): icmp_seq=207 ttl=117 time=105 ms Terminated gaurav@ubuntu:~$
Here, the “
ping youtube.com” process is now killed and the “
ping bbc.com” is still running on the terminal.
In case, if we had used the
pkill ping command, it would have killed both the
ping processes, which is undesirable.
Signals used with
pkill forces a process to quit by sending a specific signal to that process. There are three possible signals which
pkill command could send to the process depending upon the command which the user gives.
Following is the list of the signals available.
|reloads the process specified|
|kills the process specified|
|gently stops or aborts the process specified|
For this tutorial, we will be relying heavily on the
KILL signal. Let us go through some examples to understand it better.
pgrep command to get the
pid matching against the name apache.
gaurav@ubuntu:~$ pgrep apache 1218 10402 10403 gaurav@ubuntu:~$
pkill -KIll apache
OR you can also use the command with numbers (eg. 1, 9, 15)
pkill -9 apache
Both the commands shown above will kill the process apache. Confirming with the
pgrep command again.
gaurav@ubuntu:~$ pgrep apache gaurav@ubuntu:~$
pgrep command returns no output, proves that the process apache has been killed.
In this tutorial, we learnt about the
pkill command and how it is used to kill the process using the process name directly. We also learnt about the
pgrep command which is used to fetch the process id of the process run by any specific user. The
pgrep command allows us to cross-check if the process is killed.