Which Ruby version am I really running?

On your terminal, try running:

which -a ruby

This will output all the installed Ruby versions (via RVM, or otherwise) on your system in your PATH. If 1.8.7 is your system Ruby version, you can uninstall the system Ruby using:

sudo apt-get purge ruby

Once you have made sure you have Ruby installed via RVM alone, in your login shell you can type:

rvm --default use 2.0.0

You don't need to do this if you have only one Ruby version installed.

If you still face issues with any system Ruby files, try running:

dpkg-query -l '*ruby*'

This will output a bunch of Ruby-related files and packages which are, or were, installed on your system at the system level. Check the status of each to find if any of them is native and is causing issues.

Run this command:

rvm get stable --auto-dotfiles

and make sure to read all the output. RVM will tell you if something is wrong, which in your case might be because GEM_HOME is set to something different then PATH.

The ruby version 1.8.7 seems to be your system ruby.

Normally you can choose the ruby version you'd like, if you are using rvm with following. Simple change into your directory in a new terminal and type in:

rvm use 2.0.0

You can find more details about rvm here: http://rvm.io Open the website and scroll down, you will see a few helpful links. "Setting up default rubies" for example could help you.

Update:To set the ruby as default:

rvm use 2.0.0 --default