work around a goofy problem in upstart

workaround-upstart-snafu

#!/usr/bin/env perl

# occasionally when you're designing upstart services in /etc/init/whatever.conf
# you pick the wrong 'no expect' `expect fork` or `expect daemon` and upstart beings 
# tracking a pid that is already dead. It'll be stuck there refusing to start or stop the service until
# it tracks the pid exiting again. So this script forkexists over and over and over until it gets the pid
# upstart is waiting for, then exits.

# NOTE: sometimes the upstart user prevents this from working, if applicable
# ssh to localhost to make sure our ppid is 1 after we die.
# The script attempts to detect this scenerio and exists with either:
#   "really might work" or
#   "need to use ssh trick, see notes in file"
#
# ssh localhost workaround-upstart-snafu $stupidpid

use strict;
use POSIX qw(setsid);

my $target = shift;
die "pid?" unless $target and int $target;
die "... er, that's running" if -d "/proc/$target";

my $ppid = $$;

$SIG{USR1} = sub { print "we did it!! \\o/\n"; exit 0 };

while( my $pid = fork ) {
    waitpid($pid, 0);
}

print "hai, I'm $$\n";
if( $$ == $target ) {
    setsid();
    kill 10, $ppid;
    sleep 2;
    my $_ppid = getppid();
    print "\n\nexiting... old ppid=$ppid, new ppid=$_ppid", ($_ppid == 1 ? " (might really work)" : " (need to use ssh trick, see notes in file)"), "\n\n";
    exit 1;
}