Ubuntu 11.04 Ruby on Rails install write permissions error

I am trying to install rails and have installed rvm and am trying to install rails but it is saying I do not have write permissions.

$ gem install rails --version 3.0.7
    ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions into the /var/lib/gems/1.8 directory.

When I try sudo it give me this error, I know that you can use --no-ri --no-r-doc but even when I did this rails was not installed properly. Does anyone have any ideas?

$ sudo gem install rails --version 3.0.7
Successfully installed rails-3.0.7
1 gem installed
Installing ri documentation fo开发者_开发百科r rails-3.0.7...
file 'lib' not found
Installing RDoc documentation for rails-3.0.7...
file 'lib' not found

from my experience with rvm, gems should't stay in /var/lib/

if you didn't specifically asked for this, there might be a problem with your rvm installation

if so, i would definetly recommend a clean rvm install by following ryan bigg's guide of installing rvm. i followed it every time and never ever had the slightest problem after.

hope this helps!