Your kill command is backwards.
Like many UNIX commands, options that start with a minus must come first, before other arguments.
If you write
kill -INT 0
it sees the -INT as an option, and sends SIGINT to 0 (0 is a special number meaning all processes in the current process group).
But if you write
kill 0 -INT
it sees the 0, decides there's no more options, so uses SIGTERM by default. And sends that to the current process group, the same as if you did
kill -TERM 0 -INT
(it would also try sending SIGTERM to -INT, which would cause a syntax error, but it sends SIGTERM to 0 first, and never gets that far.)
So your main script is getting a SIGTERM before it gets to run the wait and echo DONE.
Add
trap 'echo got SIGTERM' TERM
at the top, just after
trap 'killall' INT
and run it again to prove this.
As Stephane Chazelas points out, your backgrounded children (process1, etc.) will ignore SIGINT by default.
In any case, I think sending SIGTERM would make more sense.
Finally, I'm not sure whether kill -process group is guaranteed to go to the children first. Ignoring signals while shutting down might be a good idea.
So try this:
#!/bin/bash
trap 'killall' INT
killall() {
trap '' INT TERM # ignore INT and TERM while shutting down
echo "**** Shutting down... ****" # added double quotes
kill -TERM 0 # fixed order, send TERM not INT
wait
echo DONE
}
./process1 &
./process2 &
./process3 &
cat # wait forever
