Unable to use ruby-debug

I'm trying to use ruby-debug but when I try to start the server with it,
I get an error saying I need to install it (even though it's installed):

tiberius:project Jonathan$ sudo gem install ruby-debug
Building native extensions. This could take a while...
Successfully installed ruby-debug-base-0.10.4
Successfully installed ruby-debug-0.10.4
2 gems installed
Installing ri documentation for ruby-debug-base-0.10.4...
Installing ri documentation for ruby-debug-0.10.4...
Installing RDoc documentation for ruby-debug-base-0.10.4...
Installing RDoc documentation for ruby-debug-0.10.4...

tiberius:project Jonathan$ rails server --debug
=> Booting WEBrick
=> Rails 3.0.0 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

tiberius:project Jonathan$ gem list

*** LOCAL GEMS ***
...
ruby-debug (0.10.4)
ruby-debug-base (0.10.4)
...

The gem also appears to run okay:

tiberius:project Jonathan$ irb

require 'ruby-debug'

=> true

Any idea why it's not working?

In Rails 3 you need to include the gem in Gemfile

gem 'ruby-debug'

Cheers!
Arzumy

If you're using ruby1.9.2 try:

group :development, :test do
   gem 'ruby-debug19', :require => "ruby-debug"
end

in your Gemfile.

I'd imply you should update to Rails 3.0.1 because of a security-update for nested attributes (if you use 'em).

That did the trick! I just converted over to Rails 3 so I wasn't aware
of the Gemfile requirement. smbepiec, thanks for the suggestion -- it
will come in handy when I update to Ruby 1.9.2.

Arzumy MD wrote in post #960061:

you will also need to type the following at the prompt:

bundle install

FYI: when replying get into the habit of bottom posting, it's easier to follow thread

Rajinder Yadav wrote in post #960332:

you will also need to type the following at the prompt:

bundle install

FYI: when replying get into the habit of bottom posting, it's easier to
follow thread

Thanks Rajinder!