1) Установка пакетного менеджера rvm:
open vim
\curl -sSL https://get.rvm.io | bash -s stable
reopen a vim
rvm -v
2) Установка ruby:
sudo apt-get purge ruby (this will remove old ruby that is not installed by rvm)
rvm list known (this will show available ruby versions)
rvm install 2.2.0 (it's quite smart, will do a lot check, might take a while)
setup GEM_HOME, and choose ruby version via rvm use ruby-2.2.0 (I didn't use this way, for some reason)
or, put ~/.rvm/rubies/ruby-2.2.0/bin to your PATH, by hand, (I use this way, because I have a common config file for such things)
reboot or re-login or source some_file, (depends on your configuration)
ruby -v
3) Установка Ruby on Rails:
gem install rails (install to "current_ruby/bin/" inside rvm folder,)
rails -v
done