Installing the latest ruby on rails on any ubuntu :lynx,karmic ....

I needed to have the latest rails on my ubuntu desktop : lucid lynx (the one that is by default in repository is too old)

and this command will not work on any debian based system because it's disabled and
it will break the debian way

sudo gem update --system

anyway you can update and the replace the gem installed on the system this way

sudo gem install rubygems-update
sudo update_rubygems

if it's not in the path (I wonder why is not there by default when the gem package is installed)
you can do this

sudo  /var/lib/gems/1.8/bin/update_rubygems 
RubyGems 1.3.6 installed

=== 1.3.6 / 2010-02-17
changelog and notices
--------------------------------

RubyGems installed the following executables:
 /usr/bin/gem1.8

then you can install the latest stable rails

sudo gem install rails