How do you kill all child processes without killing the parent

Question

I have a script which runs a background process at the beginning, then towards the end needs to stop that background process and its children, THEN do some other tasks etc t

Answer 1

To expand on Ed Heal's comment:

In the parent process, trap SIGTERM, eg

trap "echo received sigterm" SIGTERM

Then, when you want to terminate all the child processes, in the main script do

kill -s SIGTERM 0

The parent will also receive SIGTERM, but that doesn't matter, since it's trapped that signal.

You may also find it useful to set a trap for EXIT in the child processes so they can clean up when they receive SIGTERM.

You could send the child processes SIGKILL, but that's a bit brutal, and the child processes won't have a chance to do any clean up.

---

edit

Here are some scripts that illustrate how a parent script can kill its children individually, rather than en masse using kill -s SIGTERM 0.

traptest

#!/bin/bash

# trap test
# Written by PM 2Ring 2014.10.23

myname=$(basename "$0")
child=sleeploop
delay=${1:-5}
loops=${2:-5}

sig=SIGTERM 
# sig=SIGKILL 
# sig=SIGINT 

# killed=False

signal_children()
{
    killed=True
    for ipid in "${pids[@]}"
    do 
        echo "Sending $sig to $ipid"
        kill -s $sig $ipid
    done
}

set_INT_trap()
{
    msg="echo -e \"\n$myname received ^C, sending $sig to children\""
    trap "$msg; signal_children" SIGINT
}

trap "echo \"bye from $myname\"" EXIT

pids=()
for i in A B C;do 
    echo "running $child $i $delay ..."
    ./$child $i $delay  &
    pid=$!
#     echo -e "$child$i PID = $pid\n"
    pids+=($pid)
done
# echo "all child PIDs: ${pids[@]}"

echo "$myname PID = $$"
echo; ps; echo

set_INT_trap $sig
trap "echo $myname Received SIGTERM; signal_children" SIGTERM

echo "$myname sleeping..."
sleep 18 &
wait $!
echo "$myname awake"

[[ $killed != True ]] && { echo "$myname sending $sig"; signal_children; }

echo "$myname finished"

sleeploop

#!/bin/bash

# child script for traptest
# Written by PM 2Ring 2014.10.23

myname="$(basename "$0")$1"
delay=$2
loops=${3:-5}

set_trap()
{
    sig=$1
    trap "echo -e '\n$myname received $sig signal';exit 0" $sig
}

trap "echo \"bye from $myname\"" EXIT
set_trap SIGTERM
# set_trap SIGINT

#Select sleep mode
if false
then
    echo "$myname using foreground sleep"
    Sleep()
    {
        sleep $delay
    }
else
    echo "$myname using background sleep"
    Sleep()
    {
        sleep "$delay" &
        wait $!
    }
fi

#Time to snooze :)
for ((i=0; i<loops; i++));
do
    echo "$i: $myname sleeping for $delay"
    Sleep
done

echo "$myname terminated normally"

This even works if you want to pipe the output of traptest, eg try

{ ./traptest; echo >&2 exitcode $?; } | cat -n

Answer 2

You need to capture the value of $! (the child PID) right after

/some_process_with_child_processes &
pid=$!
./do_stuff
kill $pid
./do_other_stuff