Rails does not include a config/staging.rb file in it’s default blueprint for a new project.
This can provoke problems when you try to run the server for the staging environment and the file does not exist. It happened to me while trying out a vagrant machine and there was a unicorn script in init.d
Solution: make sure this file exists when you want to run this mode. I got crazy!
I suggest that the rails software created this file by default. The reason not to do it is to avoid cumbersome initial installation. But it is somehow widely extended in the community that there are four environments: