摘要：
https://www.ibm.com/developerworks/cn/linux/l-cn-usagecounter/index.html https://blog.csdn.net/younger_china/article/details/54707773 阅读全文
摘要：
http://blog.51cto.com/leejia/1952482 http://blog.51cto.com/laoxu/1267097 阅读全文