I have an app that I am migrating from Ruby to JRuby (due to need for better Web Service Security support via Java). One of the gems I use is daemons to create a background
There is an alternative, called Spoon written by Charles Nutter. See his blog http://blog.headius.com/2009/05/fork-and-exec-on-jvm-jruby-to-rescue.html and the gist https://gist.github.com/321084 for an example.