postgres, ubuntu how to restart service on startup? get stuck on clustering after instance reboot

I have a `Postgres db 9.1` running on `AWS EC2`, with `ubuntu 12.04`. I messed a lot with the instance (i.e installed all kinds of postgres X.X before i settled on 9.1). Now after a month working on that db, I discovered that if I restart my instance `postgres` doesn't load correctly, its status says "Running clusters". this will last forever until I sudo service postgresql restart from terminal, and then it works again. How do I add this line, to ubuntu startup so that each time it loads, it will restart this service, and hopefully solve my problem? Also any other solution which might solve this.