Ruby-on-rails – Set Ruby on Rails on Ubuntu 11.04

/usr/local/lib/site_ruby/1.8/rubygems/dependency.rb:247:in `to_specs': Could not find rails (>= 0) amongst [] ( Gem::LoadError)
 from /usr/local/lib/site_ruby/1.8/rubygems/dependency.rb:256:in `to_spec'
 from /usr/local/lib/site_ruby/1.8/rubygems .rb:1182:in `gem'
 from /usr/bin/rails:18

I am new to developing rails applications. I am trying to set everything up on Ubuntu 11.04. I have installed RVM (1.8.7 and 1.9 .2) And installed rubygems. But when I try to install rails using

sudo gem install rails

I get this error:

/usr/local/lib/site_ruby/1.8/rubygems/dependency.rb:247:in `to_specs': Could not find rails ( >= 0) amongst [] (Gem::LoadError)
 from /usr/local/lib/site_ruby/1.8/rubygems/dependency.rb:256:in `to_spec'
 from /usr/local /lib/site_ruby/1.8/rubygems.rb:1182:in `gem'
 from /usr/bin/rails:18

Any help would be greatly appreciated. Thank you very much in advance!

If you have installed RVM, you should not use sudo to install gems. Also, from your previous comments, you may already be in the root user’s HOME RVM is installed in the directory, which is not what you want.
You should be able to follow this guide written by Ryan Bigg, which contains a very good explanation on how to set up RVM and Rails on Ubuntu.