8 examples of using killall command to terminate processes in Linux

The Linux command line provides many commands to kill processes. For example, you can kill a process by passing a PID to the kill command; the pkill command takes a regular expression as input, so processes that match the pattern are killed.

But there is also a command called killall, which by default matches the argument name exactly and kills the matching processes. In this article, we will discuss some practical applications of this command.

By default, the killall command will send a SIGTERM signal to a process/group, but it is also possible to send a specific signal via an argument.

Below we introduce the eight usages of killall in detail with examples.

1. Basic usage

Suppose we have three processes running, namely hello1, hello2, hello3, and now we want to kill the hello1 process, we can directly use the following method:

killall hello1

The results of the operation are as follows:

[alvin@VM_0_16_centos test]$ ps aux | grep hello 
alvin 12061 0.0 0.0 4152 344 pts/0 S 14:41 0:00 ./hello1 
alvin 12074 0.0 0.0 4152 344 pts/0 S 14:41 0:00 ./hello2 
alvin 12084 0.0 0.0 4152 340 pts/0 S 14:41 0:00 ./hello3 
alvin 12089 0.0 0.0 112648 964 pts/0 R+ 14:41 0:00 grep --color=auto hello 
[alvin@VM_0_16_centos test]$ killall hello1 
[1] Terminated ./hello1 
[alvin@VM_0_16_centos test]$ ps aux | grep hello 
alvin 12074 0.0 0.0 4152 344 pts/0 S 14:41 0:00 ./hello2 
alvin 12084 0.0 0.0 4152 340 pts/0 S 14:41 0:00 ./hello3 
alvin 12170 0.0 0.0 112648 964 pts/0 R+ 14:42 0:00 grep --color=auto hello

As you can see, the hello1 process has been killed.

We want to kill the remaining hello2 and hello3 processes at once, that is, batch kill the processes, which can be done as follows:

[alvin@VM_0_16_centos test]$ killall hello* 
hello: no process found 
hello1: no process found 
hello.c: no process found 
[2]- Terminated ./hello2 
[3]+ Terminated ./hello3

In this way, all processes starting with hello are killed.

2. Terminate a process run by a user

We can kill a group of processes that match a regular expression, and similarly, we can kill all processes run by a certain user.

For example, user harry currently runs the following processes:

[alvin@VM_0_16_centos test]$ ps aux | grep harry 
root 13675 0.0 0.2 148236 5584 ? Ss 14:55 0:00 sshd: harry [priv] 
harry 13677 0.0 0.1 148236 2944 ? S 14:55 0:00 sshd: harry@pts/1 
root 13678 0.0 0.2 148236 5444 ? Ss 14:55 0:00 sshd: harry [priv] 
harry 13680 0.0 0.1 148236 2252 ? S 14:55 0:00 sshd: harry@notty 
harry 13681 0.0 0.1 53228 2168 ? Ss 14:55 0:00 /usr/libexec/openssh/sftp-server 
harry 13694 0.0 0.1 116436 3252 pts/1 Ss+ 14:55 0:00 -bash 
harry 13948 0.0 0.0 4152 344 pts/1 S 14:57 0:00 ./hello1 
harry 13952 0.0 0.0 4152 344 pts/1 S 14:57 0:00 ./hello2 
harry 13959 0.0 0.0 4152 344 pts/1 S 14:57 0:00 ./hello3 
alvin 14005 0.0 0.0 112648 964 pts/0 R+ 14:58 0:00 grep --color=auto harry

We now want to kill all processes run by harry, which can be done as follows:

killall -u harry

The results are as follows:

[alvin@VM_0_16_centos test]$ sudo killall -u harry 
[alvin@VM_0_16_centos test]$ ps aux | grep harry 
alvin 14040 0.0 0.0 112648 964 pts/0 R+ 14:58 0:00 grep --color=auto harry

However, this option should be used with caution, because it will kill all processes of the user, including terminal processes, and will cause the user to exit directly. So, don't try this option lightly if you don't want to get beaten.

3. Terminate the process at the end of time

If we are running many programs now, and we only want to kill the processes that have been running for more than 5 hours, we can use the -o option, where o stands for older as follows:

killall -o 5h

Similarly, if you want to kill processes that have been running for less than 4 hours, you can use the -y option, where y stands for younger, as follows:

killall -y 4h

These two options are also very rough and will exit the terminal, so I will not demonstrate them for now.

4. Ignore case

By default, killall command is case sensitive, so if we write it in the wrong case, it will not kill the process correctly.

[alvin@VM_0_16_centos test]$ killall HELLO1 
TEST1: no process found

If we want to ignore case, we can add the -I (uppercase i) option.

[alvin@VM_0_16_centos test]$ killall -I HELLO1 
[1] Terminated ./hello1

5. Turn off command execution echo

By default, killall will tell you the command execution status, but what if we don’t care about its execution results and just want it to execute silently? Just add the -q option, where q stands for quite, as follows:

[alvin@VM_0_16_centos test]$ killall HELLO2 
HELLO2: no process found 
[alvin@VM_0_16_centos test]$ killall -q HELLO2 
[alvin@VM_0_16_centos test]$

6. List all supported signals

As mentioned earlier, by default, the killall command will send the SIGTERM signal, but can it send other signals? Of course you can. You can use the -l option to view all the signals supported by killall:

[alvin@VM_0_16_centos test]$ killall -l 
HUP INT QUIT ILL TRAP ABRT IOT BUS FPE KILL USR1 SEGV USR2 PIPE ALRM TERM 
STKFLT CHLD CONT STOP TSTP TTIN TTOU URG XCPU XFSZ VTALRM PROF WINCH IO PWR SYS 
UNUSED

You can send a special signal to a process using the -s option followed by a signal name.

7. Interactive Operation

If you are not sure about killing multiple processes and are worried about killing processes that should not be killed, you can use the -i option, which allows you to freely decide which processes should be killed and which should be retained.

[alvin@VM_0_16_centos test]$ killall -i hello* 
Kill hello2(13825) ? (y/N) y 
Kill hello3(13831) ? (y/N) N 
hello: no process found 
hello1: no process found 
hello3: no process found 
hello.c: no process found 
[2]- Terminated ./hello2

8. Wait until a process is terminated

When a signal is sent to a process, if you want to make sure that the process has been killed before returning the execution result, you can use the -w option, where w stands for wait, as follows:

[alvin@VM_0_16_centos test]$ killall -w hello1 
[4]+ Terminated ./hello1

It seems that there is no effect here, but when it is actually executed, you can find that the execution result will appear after one or two seconds. Without the -w option, the execution result will be displayed immediately.

Summarize

The above is a detailed explanation of the 8 usage examples of using the killall command to terminate a process in Linux. I hope it will be helpful to you. If you have any questions, please leave me a message and I will reply to you in time. I would also like to thank everyone for their support of the 123WORDPRESS.COM website!
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