Install Ruby on Rails on Ubuntu

• sudo apt-get install ruby
• wget http://rubyforge.org/frs/download.php/45905/rubygems-1.3.1.tgz
• tar -xvzf rubygems-1.3.1.tgz
• rm rubygems-1.3.1.tgz
• cd rubygems-1.3.1
• sudo ruby setup.rb
• cd ..
• rm -r rubygems-1.3.1
• sudo apt-get install rubygems1.9
• sudo gem install rails mongrel

Complete
http://www.rubyinside.com/how-to-install-a-ruby-18-stack-on-ubuntu-810-from-scratch-1566.html