Instalar o git:
sudo apt-get update
sudo apt-get install git-core curl zlib1g-dev build-essential libssl-dev libreadline-dev libyaml-dev libsqlite3-dev libxml2-dev libxslt1-dev libcurl4-openssl-dev software-properties-common libffi-dev
Instalar o rbenv:
git clone https://github.com/rbenv/rbenv.git ~/.rbenv
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc