rails 3
Install environment:
sudo aptitude install build-essential libopenssl-ruby libfcgi-dev
sudo aptitude install ruby irb rubygems ruby1.8-dev
sudo aptitude install sqlite3 libsqlite3-dev

Using the gem update system:
sudo gem update --system
? Using the gem designed to update troublesome systems:
sudo gem install rubygems-update
sudo update_rubygems
? Using setup.rb, which is provided with rubygems-update:
sudo gem install rubygems-update
cd /var/lib/gems/1.8/gems/rubygems-update-*
sudo ruby setup.rb
? Finally, installing from source:
wget http://rubyforge.org/frs/download.php/69365/rubygems-1.3.6.tgz
tar xzf rubygems-1.3.6.tgz
cd rubygems-1.3.6
sudo ruby setup.rb