Why doesn't "rails s" work from the app directory?

It seems to think you are not in a rails directory (your output is saying the only valid way to use rails is with rails new).

Depending on your version, Rails identifies this differently. On 3.2, it checks for a file at script/rails. Now that 4.0 has been released, it looks for either script/rails or bin/rails (https://github.com/rails/rails/blob/207fa5c11ddf1cfd696f0eeb07d6466aae9d451e/railties/lib/rails/app_rails_loader.rb#L6)

Presumably you can get around this by creating the file rails in your script directory (if you do not have a script directory, create one in the root of your app):

#!/usr/bin/env ruby# This command will automatically be run when you run "rails" with Rails 3 gems installed from the root of your application.APP_PATH = File.expand_path('../../config/application',  __FILE__)require File.expand_path('../../config/boot',  __FILE__)require 'rails/commands'

Of course, it's worth wondering why you don't have this file in the first place. Might be worth making sure your rails is the version you want to be using first (rails -v if the version is newer, this post will show you how to create the new app using the older version).

Possible reasons:

• you are not in a directory that contains a full rails app
• your bin directory might me empty, try to run rake rails:update:bin (for Rails 4) or rails app:update:bin (Rails 5)

All the above answers didn't help me. What solved my problem for Rails 4 was to run command in the root directory of my application:

rake rails:update:bin

After that running rails s was running as expected.