Upstart: What is the first tracked PID w/o expect, but with script AND exec?

I have some Upstart configs used to start some foreground and blocking processes to run in the background as some kind of "daemons", especially those processes do not fork in any case. What I want is to restart them automatically if they exit for any unknown reason, so I configured respawn, but because those processes don't fork, I DIDN'T configure expect. That seemed to work as expected, but recently I changed something and today came across something in the Upstart cookbook again which made me wonder...

If you do not specify the expect stanza, Upstart will track the life cycle of the first PID that it executes in the exec or script stanzas.

I do use a script stanza to build the classpath for my "daemon" and recently added some waiting for Postgres and/or some web applications to become ready and execute my process afterwards using exec in that script stanza. For waiting I use tools like ps and curl, because I forgot about the "first PID thing" and seem to have confused Upstarts exec with that of the shell executing the script.

One example config:

script
  waitForPostgres()
  {
    while [ true ]
    do
      # http://superuser.com/questions/597549/grep-fails-in-upstart-script
      if ps ax | grep "[p]ostgres: wal writer process" > /dev/null
      then
        break
      fi
      sleep 10s
    done
  }
  waitForPostgres
  cd "$basePath"
  CLASSPATH=$basePath/lib
  for i in `ls $basePath/lib/*.jar`
  do
    CLASSPATH=$CLASSPATH:$i
  done
  export CLASSPATH
  exec java [...]
end script

The waitForPostgres stuff is new and from my understanding everything else are shell built-ins and without waitForPostgres the first executed and therefore tracked process should be java. But with my additional function I suspect that Upstart tracks ps instead and that obviously wouldn't be what I want.

So, which PID is tracked in this example, that of ps, grep or java and why?

And if not java is tracked, any ideas for workarounds to track that last PID instead of the first?

Thanks!

Asked by user308859 (818 )
Aug 28, 2015 at 08:14