Normally when rails environment is run by typing. This just runs the default environment which is usually development

rails s

The specific environment can be selected by using the flag -e for example:

rails s -e test

Which will run the test environment.

The default environment can be changed in terminal by editing the ~/.bashrc file, and adding the following line:

export RAILS_ENV=production in your 

If running on a remote server that is using Passenger change apache.conf to to the environment you want to use. For example this case you see RailsEnv production.

<VirtualHost *:80>
  ServerName application_name.rails.local
  DocumentRoot "/Users/rails/application_name/public"
  RailsEnv production ## This is the default
</VirtualHost>