I'm running Ubuntu server and am looking or a server monitoring utility that is open source/free. We don't need any thing too fancy. Mainly we want to know when the server is offline or if any core services have issues. Preferably something that can send us text messages or emails would be great.

**Update**

I plan on making this external than the system it's monitoring. At most it will monitor 3 servers.

**Update**

I'd like to get something that looks professional.