Bash running multiple program and handling close

background-processbashkillshell-script

I have a bash script that runs multiple programs

#!/bin/sh
python program1.py &
python program2.py &
other programs ... &
lastProgram

I run it as ./myscript.sh

When I hit Ctrl+C to close the lastProgram it exit and all the other ones keep running in the background. The problem is that the other programs need to be terminated.

Which is the proper way to handle the closing of all the programs started from the script?

Best Answer

Collect the process ID's, kill the background processes on exit.

#!/bin/bash
killbg() {
        for p in "${pids[@]}" ; do
                kill "$p";
        done
}
trap killbg EXIT
pids=()
background job 1 & 
pids+=($!)
background job 2... & 
pids+=($!)
foreground job

Trapping EXIT runs the function when the shell exits, regardless of the reason. You could change that to trap killbg SIGINT to only run it on ^C.

This doesn't check if one of the background processes exited before the script tries to shoot them. If they do, you could get errors, or worse, shoot the wrong process.

Or kill them by job id. Let's read the output of jobs to find out which ones are still active.

#!/bin/bash 
killjobs() {
    for x in $(jobs | awk -F '[][]' '{print $2}' ) ; do 
        kill %$x
    done
}
trap killjobs EXIT
sleep 999 &
sleep 1 &
sleep 999 &
sleep 30

If you run background processes that spawn other processes (like a subshell: (sleep 1234 ; echo foo) &), you need to enable job control with set -m ("monitor mode") for this to work. Otherwise just the lead process is terminated.

Related Solutions

Bash – Script ends abruptly with a Terminated message

When you are calling pkill -f resque it is also matching your script, sending it a SIGTERM. If you are unable to add additional restrictions on the pkill commands such as more exact matching, you will need to kill PIDs one at a time to ensure the script is not killing itself. Here is an example:

pids=( $(pgrep -f resque) )
for pid in "${pids[@]}"; do
  if [[ $pid != $$ ]]; then
    kill "$pid"
  fi
done

Shell – What happens to background jobs after exiting the shell

When the shell exits, it might send the HUP signal to background jobs, and this might cause them to exit. The SIGHUP signal is only sent if the shell itself receives a SIGHUP, i.e. only if the terminal goes away (e.g. because the terminal emulator process dies) and not if you exit the shell normally (with the exit builtin or by typing Ctrl+D). See In which cases is SIGHUP not sent to a job when you log out? and Is there any UNIX variant on which a child process dies with its parent? for more details. In bash, you can set the huponexit option to also send SIGHUP to background jobs on a normal exit. In ksh, bash and zsh, calling disown on a job removes it from the list of jobs to send SIGHUP to. A process that receives SIGHUP may ignore or catch the signal, and then it won't die. Using nohup when you run a program makes it immune to SIGHUP.

If the process isn't killed due to a possible SIGHUP then it remains behind. There's nothing left to relate it to job numbers in the shell.

The process may still die if it tries to access the terminal but the terminal no longer exists. That depends how the program reacts to a non-existent terminal.

If the job contains multiple processes (e.g. a pipeline), then all these processes are in one process group. Process groups were invented precisely to capture the notion of a shell job that is made up of multiple related processes. You can see processes grouped by process group by displaying their process group ID (PGID — normally the process ID of the first process in the group), e.g. with ps l under Linux or something like ps -o pid,pgid,tty,etime,comm portably.

You can kill all the processes in a group by passing a negative argument to kill. For example, if you've determined that the PGID for the pipeline you want to kill is 1234, then you can kill it with

kill -TERM -1234

Best Answer

Related Solutions

Bash – Script ends abruptly with a Terminated message

Shell – What happens to background jobs after exiting the shell

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