rails s -u ignores ruby-debug gem

Try adding 'gem "ruby-debug"' to your Gemfile, that should do the trick.

i am facing the similar problem too.
adding 'gem "ruby-debug"' to Gemfile gives me an error like this

vibhas-MacBook:rawspot vibhachadha$ r s --debugger
/Users/vibhachadha/.rvm/gems/ruby-1.9.1-p378/gems/bundler-0.9.10/lib/bundler/resolver.rb:52:in block in resolve': No compatible versions could be found for required dependencies: (Bundler::VersionConflict)

ruby-debug-base (~> 0.10.3.0, runtime) not found in any of the sources
  required by ruby-debug (>= 0, runtime)
All possible versions of origin requirements conflict.
from /Users/vibhachadha/.rvm/gems/ruby-1.9.1-p378/gems/bundler-0.9.10/lib/bundler/resolver.rb:39:in `catch'
from /Users/vibhachadha/.rvm/gems/ruby-1.9.1-p378/gems/bundler-0.9.10/lib/bundler/resolver.rb:39:in `resolve'
from /Users/vibhachadha/.rvm/gems/ruby-1.9.1-p378/gems/bundler-0.9.10/lib/bundler/runtime.rb:93:in `specs'
from /Users/vibhachadha/.rvm/gems/ruby-1.9.1-p378/gems/bundler-0.9.10/lib/bundler/runtime.rb:82:in `specs_for'
from /Users/vibhachadha/.rvm/gems/ruby-1.9.1-p378/gems/bundler-0.9.10/lib/bundler/runtime.rb:18:in `setup'
from /Users/vibhachadha/.rvm/gems/ruby-1.9.1-p378/gems/bundler-0.9.10/lib/bundler.rb:66:in `setup'
from /Users/vibhachadha/rawspot/config/boot.rb:7:in `rescue in <top (required)>'
from /Users/vibhachadha/rawspot/config/boot.rb:2:in `<top (required)>'
from /Users/vibhachadha/rawspot/script/rails:9:in `require'
from /Users/vibhachadha/rawspot/script/rails:9:in `<main>'

ruby-debug (0.10.3)
ruby-debug-base19 (0.11.23)
ruby-debug-ide (0.4.9)
ruby-debug19 (0.11.6) gems are already installed on my machine. I am running my app on ruby 1.9.1 and rails 3

Any suggestions ?
Please help

(from [a509b0b18fd02d1d712248ce94e1d36750d58565]) Revert "Ruby 1.9: use ruby-debug19. [#3949 rails s -u ignores ruby-debug gem state:resolved]"

This wasn't the issue here; we need to beef up the docs and speak to
Wayne and Mark about installation.

This reverts commit da238dafd7c242eb75ae37e6243b61baf763e3d0.
http://github.com/rails/rails/commit/a509b0b18fd02d1d712248ce94e1d3...

(from [4fbcde43e3122914334d706ea9d4d30151a1368d]) Ruby 1.9: use ruby-debug19. [#3949 rails s -u ignores ruby-debug gem state:resolved] http://github.com/rails/rails/commit/4fbcde43e3122914334d706ea9d4d3...

(from [b94c4080e5ba738b76b44d954bd8b13ff13e8688]) Revert "Ruby 1.9: use ruby-debug19. [#3949 rails s -u ignores ruby-debug gem state:resolved]"

This wasn't the issue here; we need to beef up the docs and speak to
Wayne and Mark about installation.

This reverts commit da238dafd7c242eb75ae37e6243b61baf763e3d0.
http://github.com/rails/rails/commit/b94c4080e5ba738b76b44d954bd8b1...