ruby on rails

I wanted to try ruby-debug as described in the book by Patrick Lenz Simply Rails 2.0 in chapter 11. I installed the gem with »sudo gem install ruby-debug«. The following error I got staring the server with debug option prevented me from carrying on with the lesson:

USER@COMPUTER:/var/www/ror$ rails server –debug
=> Booting Mongrel
=> Rails 3.0.3 application starting in development on http://0.0.0.0:3000
=> 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

I googled my ass off to find the solution. Most sites had a hint about incompatibility between ruby, rails and gems. But the solution was much more simple. Just edit the Gemfile and uncomment »gem ‚ruby-debug’« like this:

# To use debugger
gem ‚ruby-debug‘