Bash – sleep, wait and Ctrl+C propagation

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

First, exit 130 is not an abnormal exit. It is a normal exit, with exit status 130. As can be seen from man 3 wait (POSIX):

   If  the  information  pointed  to  by  stat_loc was stored by a call to
   waitpid()  that  specified  the  WUNTRACED     and  WCONTINUED   flags,
   exactly one of the macros WIFEXITED(*stat_loc), WIFSIGNALED(*stat_loc),
   WIFSTOPPED(*stat_loc),  and WIFCONTINUED(*stat_loc)  shall evaluate  to
   a non-zero value.

WIFEXITED checks normal exit, and WIFSIGNALLED is termination due to an uncaught signal. Since these are mutually exclusive, an exit 130 is normal.

That the exit status is 130 when a process dies by SIGINT is because bash sets it to be 130 outside of the process because it detected an exit due to SIGINT: Why does bash set $? (exit status) to non-zero on Ctrl-C or Ctrl-Z?

Second, a process that handles SIGINT and then dies should kill itself with SIGINT. Greg's wiki (an excellent resource for shell stuff) has a note on this:

If you choose to set up a handler for SIGINT (rather than using the EXIT trap), you should be aware that a process that exits in response to SIGINT should kill itself with SIGINT rather than simply exiting, to avoid causing problems for its caller. Thus:

trap 'rm -f "$tempfile"; trap - INT; kill -INT $$' INT

Now, if you changed the exit 130 to:

trap - INT
kill -INT $$

You'd see the expected behaviour.