How to fire and forget a subprocess?

Question

I have a long running process and I need it to launch another process (that will run for a good while too). I need to only start it, and then completely forget about it.

Answer 1

The other answers are good if you're sure you want to detach the child process. However, if you either don't mind, or would prefer to keep the child process attached (e.g. you are launching sub-servers/services for a web app), then you can take advantage of the following shorthand

fork do
    exec('whatever --option-flag')
end

Providing a block tells fork to execute that block (and only that block) in the child process, while continuing on in the parent.