Upstart kills all process started by script

Question

So I use Upstart [myscript] to start a script [A], which starts another script [B], which in turn starts some other scripts [GROUP C].

When I run stop [myscript], I encounter the unusual behavior where [GROUP C] is also stopped. Every script in [GROUP C] has been started with a &, and are running in the background. I am surprised that they are also killed by the stop [myscript] command. Why is this, and how to I prevent it from happening?

EDIT: Basically [myscript] is as follows:

pre-start script
          echo 'Starting myscript Daemon\n'
end script

script
        exec /foo/bar/myscript-start.sh
end script

post-stop script
        echo 'and apparently we are done....'
end script

Answer 1

Upstart kills the process group:

The signal specified by the kill signal stanza is sent to the process group of the main process. (such that all processes belonging to the jobs main process are killed). By default this signal is SIGTERM.

To avoid this, start the child processes in a new session with setsid, for example:

setsid top

ps (ps -eo '%c %a %p %P %r') will show that the process has a unique process group, and a parent pid of 1.

Answer 2

Seems you don't understand how scripts stanzas works.

pre-start stanza

pre-start script
          echo 'Starting myscript Daemon\n'
end script

This script start before your main scrips, if it fails, the start sequence will fails. This is normally used for some adhoc operations that will allow the first script to start, these are not daemon-like (continuously running at background). Example:

pre-start script
    /lib/init/apparmor-profile-load usr.sbin.avahi-daemon
end script

script
    opts="-D"
    [ -e "/etc/eucalyptus/avahi-daemon.conf" ] && opts="${opts} -f /etc/eucalyptus/avahi-daemon.conf"
    exec avahi-daemon ${opts}
end script

As you can see, the apparmor profile is first load from the DBus (yeah, kind of awkward if you don't know the backend of Ubuntu) then starts the service as intended. This operation is designed for process that die once executed.

script stanza

script
        exec /foo/bar/myscript-start.sh
end script

This is the only part of your program that needs to run continuously and upstart has to track it's PID. This process dies when you stop the script.

post-stop stanza

post-stop script
        echo 'and apparently we are done....'
end script

This stanzas are designed as a kind of a cleanup process. It will be executed once the main script dies gracefully. For example, apport:

post-stop script
    # Check for a hung resume.  If we find one try and grab everything
    # we can to aid in its discovery
    if [ -e /var/lib/pm-utils/status ]
    then
        ps -wwef > /var/lib/pm-utils/resume-hang.log
    fi

    if [ "`dd if=/proc/sys/kernel/core_pattern count=1 bs=1 2>/dev/null`" != "|" ]
    then
        exit 1
    else
        echo 0 > /proc/sys/fs/suid_dumpable
        echo "core" > /proc/sys/kernel/core_pattern
    fi
end script

It tries to detect a resume from sleep that was not successful and starts preparations for detect the next hang so it can produce a useful report (yeah, is complicated again, but that was the most simple script I found apart ufw which is oversimplified). As you can see each process dies by itself since it could block the shutdown of the system (in such cases there's also a script that sends TERM and KILL signals to hanged process).

Bottom line, what you are experiencing is perfectly normal and is the desired behavior of upstart.