I installed rvm with rails, from the official website of RVM, I specified the command suggested by the tutorial. When the installation my system has rails 4.0.0, rvm 01/23/1
Possible duplicate of: Ubuntu rvm setup issue
Your problem is that RVM is not loaded when you open a new terminal.
To solve this, run this command line: (if using login-shell)
echo "source $HOME/.rvm/scripts/rvm" >> ~/.bash_profile
Or this (if using non-login shell):
echo "source $HOME/.rvm/scripts/rvm" >> ~/.bashrc
This will add the path to RVM to load at each Terminal instanciation (close & re-open a terminal after you did this).