Install RVM 1.0.1
First be sure to do a quick update before you get started.
sudo apt-get update
Next install curl and git so we can pull down ruby via rvm
sudo apt-get install curl git-core
Now that you’re all set up, install RVM itself. This is done via a shell script which you can download and run directly with a single command.
$ bash < <(curl -s https://rvm.beginrescueend.com/install/rvm)
After this is complete you need to edit your .bashrc file. First cd ~ and then Type "gedit .bashrc". Put the following at the bottom of the file.
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"
after you complete the above and save your changes, close gedit. Next close your terminal window and re-open it. Now if you type "rvm -v" you should see a valid version 1.x
Install Ruby 1.8.7
First you need to pull down a few development packages
sudo apt-get install libruby1.8 zlib1g-dev libssl-dev libreadline5-dev build-essential
Next you need to install ruby 1.8.7 through rvm
rvm install ruby-1.8.7
After this is complete you need to set ruby 1.8.7 as the default for rvm
rvm use ruby-1.8.7 --default
Install rubygems and other dev essentials
first you need to add the ubuntu-on-rails ppa repository, sometimes they have newer versions of some Ruby components.
sudo add-apt-repository ppa:ubuntu-on-rails
After you add this be sure to do another update
sudo apt-get update
Next install the essential ruby packages
sudo apt-get install ruby rubygems irb ri rdoc rake
And a few more packages, odds are you will need them anyway
sudo apt-get install build-essential ruby1.8-dev libopenssl-ruby
After all the packages above are installed, add the gem path to your global PATH, so that executables new gems can be easily called from the command line.
export PATH=/var/lib/gems/1.8/bin:$PATH
After you run the above command, close the terminal window and re-open it.
Install MySql
Install the myslq development packages
sudo apt-get install mysql-server mysql-client sudo apt-get install libmysql-ruby libmysqlclient-dev
Install the mysql gem
gem install mysql
Install Ruby 1.9.2
Next you need to install ruby 1.9.2 through rvm
rvm install ruby-1.9.2
After this is complete you need to set ruby 1.9.2 as the default for rvm.
rvm use ruby-1.9.2 --default
Install Rails 3.0.3
Now install rails but be sure you DON’T use sudo
gem install rails --version 3.0.3
After you have both rails 3 and ruby 1.9.2 up and running, install the mysql gem again.
gem install mysql
Now you should have a fully functional rails 3 + ruby 1.9.2 development environment! You can verify this by doing a simple "ruby -v" and "rails -v" from the command line.
http://toranbillups.com/blog/archive/2010/09/01/How-to-install-Rails-3.0-and-Ruby-1.9.2-on-Ubuntu
http://wiki.rubyonrails.org/getting-started/installation/linux