JSON Ruby Library

I am working on an open source cloud computing project. The project being in the initial phase, I have installed Ubuntu Server 14.04 as the Front End on Oracle VM VirtualBox. When I was going as per the Design and Installation Guide, I couldn’t execute the command “$ sudo mv /usr/lib/ruby/1.8/json.rb /usr/lib/ruby/1.8/json.rb.no” in the section 1.4 Installing the Software . It says no such file or directory exists. I checked using ‘ls’ command, I couldnt find ruby folder inside “usr/lib” whereas I had successfully installed JSON. Please HELP
P.S. - Please try to keep it simple to understand.