五种概览：http://www.cnblogs.com/xiehongfeng100/p/4763225.html
http://sukai.me/linux-five-io-models/ 内有多个链接
http://www.cnblogs.com/Anker/archive/2013/08/17/3263780.html
select 等比较http://codefine.co/%E8%BD%AC%E8%BD%BD%E7%90%86%E8%A7%A3%E7%BD%91%E7%BB%9Cio%E6%A8%A1%E5%9E%8B/
ubuntu 快捷键http://yife.im/ubuntu-terminal-shortcode/