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I have a question. Studying processes management I observed a strange behavior, on a CentOS 7. I know that killing a parent process, the child processes are killed also. But not in the following case. I ran the command dd, just for example:

[root@server2 ~]# dd if=/dev/zero of=/dev/null & [1] 1756 [root@server2 ~]# ps fax | grep -B2 dd 1737 pts/2 S 0:00 \_ su - 1741 pts/2 S 0:00 \_ -bash 1756 pts/2 R 1:18 \_ dd if=/dev/zero of=/dev/null

After that I tried to kill (with SIGKILL signal) the parent process, that is the bash, but this action doesn't kill the dd process:

[root@server2 ~]# kill -9 1741 Killed [user@server2 ~]#

The shell terminates but as you can see in the top command output, the dd process is still working:

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1756 root 20 0 107948 612 512 R 99.9 0.1 10:06.98 dd

Do you have any idea about it please?

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4 Answers 4

Reset to default
15

By default killing a parent process does not kill the children processes.

I suggest you look for other questions about how to kill both the parent and child using the process group (a negative PID).

A good answer about how to do this in detail can be found at Process descendants

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2

I was in a similar situation and found the answer.

TLDR;

try: kill -2 <parent_pid>

You will know if this method will work for you, if while running your script and you press Ctrl+C would kill the parent and all spawned processes.

The reason for this is the different signals that kill can send. By default kill <pid> will send 15 <SIGTERM> signal. But the regular signal when pressing Ctrl+C is not 15 <SIGTERM> it is in fact 2 <SIGINT>.

So if you kill -2 <pid> this will kill your parent process as if having interrupted it with Ctrl+C

source

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1
  • I don't think this is quite correct. Ctrl-C kills all the processes because the of terminal magic. kill -2 will still only send it to one process. Commented Oct 10, 2023 at 10:02
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Please adjust to your own needs, especially on the kill command:

function kill_recurse() { cpids=`pgrep -P $1|xargs` for cpid in $cpids; do kill_recurse $cpid done echo "killing $1" kill -9 $1 }

Example usage would be: kill_recurse <my_parent_pid>

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For simpler cases where you don't need to recursively find grand and great-grand child processes, this will terminate the parent and child processes:

pkill -P <parent PID>
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