Install ruby on rails in Ubuntu 12.04

参考：http://ruby-china.org/wiki/install-rails-on-ubuntu-12-04-server

简述如下

1. 更改源并update

2. Install 第三方库

3. Install RVM

4. Install Ruby

5. Install Rails

安装版本

rvm -v

rvm 1.22.9 (master) by Wayne E. Seguin <[e-mail]>, Michal Papis <[e-mail]> [https://rvm.io/]

ruby -v

ruby 2.0.0p247 (2013-06-27 revision 41674) [i686-linux]

rails -v

Rails 4.0.0

SQLite3

1.3.8

碰到的问题：

Q1: There is no checksum for 'http://production.cf.rubygems.org/rubygems/rubygems-2.1.3.tgz' or 'rubygems-2.1.3.tgz', it's not possiable to validate it.

A1: rvm get stable or rvm get head

Reference: http://stackoverflow.com/questions/15378312/rvm-install-error-there-is-no-checksum-its-not-possible-to-validate-it