When running Xubuntu with xfce4-terminal, after running rvm install 2.1.1 , the following error appears:

RVM is not a function, selecting rubies with 'rvm use ...' will not work.

You need to change your terminal emulator preferences to allow login shell.
Sometimes it is required to use `/bin/bash --login` as the command.
Please visit https://rvm.io/integration/gnome-terminal/ for a example.

You need to right click the terminal, click Preferences, tick “Run command as login shell”, then click Close, then reopen the terminal and you should be able to run rvm use 2.1.1 !