I have installed Ubuntu 12.04 on VirtualBox.

I installed rvm, ruby and rails following this tutorial.

But when I restart, I am getting this error:

The program 'rails' is currently not installed.  You can install it by typing:

sudo apt-get install rails

And after that, when I again try gem install rails I am getting this error:

ERROR:  While executing gem ... (Errno::EACCES)

Permission denied - /var/lib/gems

And there is no gems folder under /var/lib/.

Can anyone help me to fix this?