The default DNS server list was reset automatically after network restarting.

chenyang@chenyang-pc:~$ cat /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 20.10.1.5
nameserver 20.10.1.6
nameserver 127.0.1.1
search ufsoft.com.cn

This config file is generated by resolvconf using template files in /etc/resolvconf/resolv.conf.d/

chenyang@chenyang-pc:~$ cat /etc/resolvconf/resolv.conf.d/head 
# 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

Modify head to

chenyang@chenyang-pc:~$ cat /etc/resolvconf/resolv.conf.d/head 
# 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 192.168.8.57
nameserver 192.168.8.119

Regenerate /etc/resolv.conf file

sudo resolvconf -u

Then the latest config is

chenyang@chenyang-pc:~$ cat /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 192.168.8.57
nameserver 192.168.8.119
nameserver 20.10.1.5
nameserver 20.10.1.6
nameserver 127.0.1.1
search ufsoft.com.cn

refs

  • http://askubuntu.com/questions/130452/how-do-i-add-a-dns-server-via-resolv-conf