How to kill a process in Linux?
Learn how to kill a running process in Linux using Kill, Pkill and Killall commands. These commands terminates processes abruptly and make sure the system continues to run.
In Linux, usually a process terminates on its own one its job is done. But sometimes a process can take up too much time and CPU and it would still keep on running. In such situations, we need to kill the process.
To kill a process, we need its pid (process id). First we will take a look at different ways to finding pid.
Locating a process using Linux commands
In Linux, every process has a pid. The kernel identifies each process using a process ID (PID), a every instance of process must have a unique PID from other processes which is assigned when the process is invoked, to avoid any execution errors.
ps command
To view the list of all running processes using the following command.
ps aux
Its output would list all the running processes with the user, pid, percentage of CPU utilization, percentage of memory consumed etc. But this command would show the processes run by the root user too.
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.1 167384 8820 ? Ss 14:59 0:08 /sbin/init persistent splash root 2 0.0 0.0 0 0 ? S 14:59 0:00 [kthreadd] root 3 0.0 0.0 0 0 ? I< 14:59 0:00 [rcu_gp] root 4 0.0 0.0 0 0 ? I< 14:59 0:00 [rcu_par_gp] root 6 0.0 0.0 0 0 ? I< 14:59 0:00 [kworker/0:0H-kblockd] root 8 0.0 0.0 0 0 ? I< 14:59 0:00 [mm_percpu_wq] root 9 0.0 0.0 0 0 ? S 14:59 0:02 [ksoftirqd/0] root 10 0.3 0.0 0 0 ? I 14:59 0:43 [rcu_sched] root 11 0.0 0.0 0 0 ? S 14:59 0:00 [migration/0] root 12 0.0 0.0 0 0 ? S 14:59 0:00 [idle_inject/0] root 14 0.0 0.0 0 0 ? S 14:59 0:00 [cpuhp/0] root 15 0.0 0.0 0 0 ? S 14:59 0:00 [cpuhp/1] root 16 0.0 0.0 0 0 ? S 14:59 0:00 [idle_inject/1] root 17 0.0 0.0 0 0 ? S 14:59 0:00 [migration/1] root 18 0.0 0.0 0 0 ? S 14:59 0:00 [ksoftirqd/1] root 20 0.0 0.0 0 0 ? I< 14:59 0:00 [kworker/1:0H-kblockd] root 21 0.0 0.0 0 0 ? S 14:59 0:00 [cpuhp/2] root 22 0.0 0.0 0 0 ? S 14:59 0:00 [idle_inject/2]
We can filter this out by using grep.
ps aux | grep william
This command would list down all the processes started by the user william.
william 1561 0.0 0.0 16800 6748 ? Ss 15:00 0:00 /lib/systemd/systemd --user william 1562 0.0 0.0 21264 2480 ? S 15:00 0:00 (sd-pam) william 1578 0.0 0.0 542848 7376 ? Sl 15:00 0:00 /usr/bin/gnome-keyring-daemon --daemonize --login william 1582 0.0 0.0 173872 5472 tty2 Ssl+ 15:00 0:00 /usr/lib/gdm3/gdm-x-session --run-script env GNOME_SHELL_SESSION_MODE=ubuntu /usr/bin/gnome-session --session=ubuntu william 1584 1.3 0.5 781140 47000 tty2 Sl+ 15:00 2:43 /usr/lib/xorg/Xorg vt2 -displayfd 3 -auth /run/user/1000/gdm/Xauthority -background none -noreset -keeptty -verbose 3 william 1596 0.0 0.0 8144 4504 ? Ss 15:00 0:00 /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only william 1599 0.0 0.1 583220 12020 tty2 Sl+ 15:00 0:00 /usr/lib/gnome-session/gnome-session-binary --session=ubuntu william 1705 0.0 0.0 5924 40 ? Ss 15:00 0:00 /usr/bin/ssh-agent /usr/bin/im-launch env GNOME_SHELL_SESSION_MODE=ubuntu /usr/bin/gnome-session --session=ubuntu william 1711 0.0 0.0 308716 5776 ? Ssl 15:00 0:00 /usr/lib/at-spi2-core/at-spi-bus-launcher william 1716 0.0 0.0 7264 3592 ? S 15:00 0:00 /usr/bin/dbus-daemon --config-file=/usr/share/defaults/at-spi2/accessibility.conf --nofork --print-address 3 william 1718 0.0 0.0 168188 5576 ? Sl 15:00 0:00 /usr/lib/at-spi2-core/at-spi2-registryd --use-gnome-session william 1739 2.1 2.3 3366092 189992 tty2 Rl+ 15:00 4:16 /usr/bin/gnome-shell william 1749 0.0 0.0 247448 6300 ? Ssl 15:00 0:00 /usr/lib/gvfs/gvfsd william 1754 0.0 0.0 377580 4964 ? Sl 15:00 0:00 /usr/lib/gvfs/gvfsd-fuse /run/user/1000/gvfs -f -o big_writes william 1766 0.1 0.1 319296 8196 tty2 Sl 15:00 0:17 ibus-daemon --xim --panel disable william 1767 0.0 0.0 243300 3972 ? Ssl 15:00 0:00 /usr/libexec/xdg-permission-store
We can also filter it using the name of the program.
ps aux | grep httpd
This command would filter out the Apache processes
root 15720 0.0 0.0 224064 2956 ? Ss 01:43 0:02 /usr/sbin/httpd -DFOREGROUND root 16209 0.0 0.0 241228 2572 pts/0 S+ 07:29 0:00 sudo vi httpd.conf root 16230 0.0 0.0 126504 1268 pts/0 S+ 07:30 0:00 vi httpd.conf schandr+ 19168 0.0 0.0 112716 960 pts/1 S+ 07:53 0:00 grep --color=auto httpd apache 25863 0.0 0.0 224196 2644 ? S 03:27 0:00 /usr/sbin/httpd -DFOREGROUND apache 25864 0.0 0.0 224196 2536 ? S 03:27 0:00 /usr/sbin/httpd -DFOREGROUND apache 25865 0.0 0.0 224196 2640 ? S 03:27 0:00 /usr/sbin/httpd -DFOREGROUND apache 25866 0.0 0.0 224196 2620 ? S 03:27 0:00 /usr/sbin/httpd -DFOREGROUND apache 25867 0.0 0.0 224196 2508 ? S 03:27 0:00 /usr/sbin/httpd -DFOREGROUND apache 26512 0.0 0.0 224196 2536 ? S 03:32 0:00 /usr/sbin/httpd -DFOREGROUND apache 26579 0.0 0.0 224196 2564 ? S 03:33 0:00 /usr/sbin/httpd -DFOREGROUND apache 26650 0.0 0.0 224196 2496 ? S 03:34 0:00 /usr/sbin/httpd -DFOREGROUND
pidof and pgrep commands
The pidof command lists down all the pids using the process name.
>pidof httpd 26650 26579 26512 25867 25866 25865 25864 25863 15720
Similarly, pgrep command lists down all the process ids using its name.
>pgrep httpd 15720 25863 25864 25865 25866 25867 26512 26579 26650
top command
top command gives you an interface where you can view more information of all processes which can be navigated using up and down keys.
top - 20:48:29 up 5:49, 1 user, load average: 3.04, 2.16, 1.56 Tasks: 387 total, 1 running, 386 sleeping, 0 stopped, 0 zombie %Cpu(s): 5.5 us, 1.6 sy, 0.0 ni, 92.7 id, 0.1 wa, 0.0 hi, 0.1 si, 0.0 st MiB Mem : 7837.3 total, 392.2 free, 2887.8 used, 4557.3 buff/cache MiB Swap: 2048.0 total, 1822.5 free, 225.5 used. 3631.3 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1739 william 20 0 3378452 204788 61564 S 11.6 2.6 5:27.05 gnome-shell 1584 william 20 0 786208 47408 34292 S 5.3 0.6 3:06.74 Xorg 7165 william 20 0 1099620 349188 125504 S 2.6 4.4 12:56.24 chrome 7632 william 20 0 987264 45048 31456 S 2.3 0.6 0:07.97 gnome-terminal- 912 root 20 0 232908 6028 5324 D 1.0 0.1 3:43.04 iio-sensor-prox 7214 william 20 0 606148 129064 83976 S 1.0 1.6 1:17.45 chrome 2151 william 20 0 389088 83624 42320 S 0.7 1.0 1:08.93 chrome 8025 william 20 0 573648 113188 75428 S 0.7 1.4 0:35.61 chrome 1009 debian-+ 20 0 185720 7340 6400 S 0.3 0.1 0:14.14 transmission-da 2092 william 20 0 1520300 554968 361468 S 0.3 6.9 4:57.96 chrome 5996 william 20 0 893088 261808 81012 S 0.3 3.3 2:03.59 chrome 7413 william 20 0 705892 215500 82012 S 0.3 2.7 1:32.96 chrome 7458 william 20 0 590140 132180 78624 S 0.3 1.6 0:49.35 chrome 8045 william 20 0 575820 101520 71952 S 0.3 1.3 0:37.83 chrome 8254 william 20 0 850964 188708 94596 S 0.3 2.4 1:22.29 chrome 8399 william 20 0 547392 87096 66932 S 0.3 1.1 0:14.28 chrome 11625 root 20 0 0 0 0 D 0.3 0.0 0:00.16 kworker/0:2+kacpid 11745 root 20 0 0 0 0 I 0.3 0.0 0:00.15 kworker/3:0-events 11882 root 20 0 0 0 0 I 0.3 0.0 0:00.23 kworker/u16:69-iwlwifi 12216 william 20 0 20660 3956 3208 R 0.3 0.0 0:00.18 top
Killing processes
When you kill a process, Linux sends a terminating signal to the process. By default, SIGTERM signal will be sent, which allows the program to interpret this signal and run some code to help the process exit gracefully. To kill a process forcibly, we can use SIGKILL signal. SIGTERM is referred as number 15 internally and SIGKILL as 9.
To kill processes, we can use various commands such as kill, pkill and killall.
kill command
To kill a process using kill command, use the following syntax
kill [signal] pid1 pid2 pidN
To send SIGKILL signal
kill -9 pid1 pid2 pidN
You can also pass SIGKILL instead of the number 9.
kill -SIGKILL 5467 4535
killall command
killall command kills a process and all its child process. This command accepts process name. Syntax would be..
kill [signal] <process_name>
Example:
kill -9 httpd
pkill command
pkill command kills a process using its name.
pkill <process_name>
Always be sure you are passing the correct process name. Sending wrong process name would screw things up.
pkill httpd
or..
pkill -9 httpd
