Kill a background job without a message

snipplet:
kill, process management, jobs
LastUpdate:
2010-07-31
Contributor:
Jan Schampera
type:
snipplet

When you start background jobs from within a script (non-interactive shell) and kill it afterwards, you will get a message from the shell that the process was terminated.

Example:

#!/bin/bash

# example background process
sleep 300 &

# get the PID
BG_PID=$!

# kill it, hard and mercyless
kill -9 $BG_PID

echo "Yes, we killed it"

You will get something like this:

$ ./bg_kill1.sh
./bg_kill1.sh: line 11:  3413 Killed                  sleep 300
Yes, we killed it

This is more or less a normal message. And it can't be easily redirected since it's the shell itself that yells this message, not the command kill or something else. You would have to redirect the whole script's output.

It's also useless to temporarily redirect stderr when you call the kill command, since the successful termination of the job, the termination of the kill command and the message from the shell may not happen at the same time. And a blind sleep after the kill would be just a workaround.

The solution is relatively easy: The shell spits that message because it controls the background job, and when it terminates, the shell will tell you whenever possible. Now you just need to tell your shell that it is no longer responsible for that background process. This is done by the disown command, which can take an internal shell job number (like %1) or a process ID as argument.

#!/bin/bash

# example background process
sleep 300 &

# get the PID
BG_PID=$!

### HERE, YOU TELL THE SHELL TO NOT CARE ANY MORE ###
disown $BG_PID
###


# kill it, hard and mercyless, now without a trace
kill -9 $BG_PID

echo "Yes, we killed it"

That way, you can run and kill background processes without disturbing messages.

Discussion

Enter your comment. Wiki syntax is allowed: