Rails not booting in debug

I did:

gem install ruby-debug

Then it installs...

I launched using:

rails server -u -p 3002

(I also tried with -d)

I get this:

=> Booting WE开发者_StackOverflowBrick
=> Rails 3.0.1 application starting in development on http://0.0.0.0:3002
=> Call with -d to detach
=> Ctrl-C to shutdown server
You need to install ruby-debug to run the server in debugging mode. With gems, use 'gem install ruby-debug'
Exiting

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You need add ruby-debug in your Gemfile

gem 'ruby-debug'