Ubuntu 15.04直接修改/etc/resolv.conf，添加DNS重启后配置丢失。

正确方法：

1. #vim /etc/network/interfaces，文件最后添加“dns-nameservers  223.5.5.5”

   重启systemctl restart networking.service，测试OK

2. #vim /etc/resolvconf/resolv.conf.d/base（文件默认为空）

   nameserver  223.5.5.5

   nameserver  223.6.6.6

   #resolvconf -u  (更新改动至resolv.conf)

   #more /etc/resolv.conf

   # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)

   #     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

   nameserver 223.5.5.5

   nameserver 223.6.6.6

   不需要重启网卡/系统，测试OK，重启系统后OK。