環境：

Ubuntu 14.04

操作過程：

1. 刪除RVM

rvm implode

其他注意事項：

Note you may need to manually remove /etc/rvmrc and ~/.rvmrc and ~/.rvm if they exist still.
Please check all .bashrc .bash_profile .profile and .zshrc for RVM source lines and delete or comment out if this was a Per-User installation.
Also make sure to remove ‘rvm’ group if this was a system installation.
Finally it might help to relogin / restart if you want to have fresh environment (like for installing RVM again).

2. 簡單兩步驟安裝rbenv

First you install rbenv, and then ruby-build

$ cd ~
$ git clone git://github.com/sstephenson/rbenv.git .rbenv
$ echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
$ echo 'eval "$(rbenv init -)"' >> ~/.bashrc
$ exec $SHELL

$ git clone git://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build
$ echo 'export PATH="$HOME/.rbenv/plugins/ruby-build/bin:$PATH"' >> ~/.bashrc
$ exec $SHELL

$ rbenv install 2.1.2
$ rbenv global 2.1.2
$ ruby -v

3. 參考網址：

Setup Ruby On Rails on Ubuntu 14.04 Trusty Tahr
move from rvm to rbenv