2.0 KiB
Kill a background job without a message
---- dataentry snipplet ---- snipplet_tags: kill, process management, jobs LastUpdate_dt: 2010-07-31 Contributors: 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.