方法一： 通过/etc/network/interfaces，在它的最后增加一句（多个dns之间用空格分隔）：
# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
auto lo
iface lo inet loopback
# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.201.100
netmask 255.255.255.0
gateway 192.168.201.254
dns-nameservers 202.97.224.68 202.97.224.69
202.97.224.68是联通的DNS服务。
重启后DNS就生效了，这时候/etc/resolv.conf文件最下面会多出一行：
# 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 202.97.224.68
nameserver 202.97.224.69
方法二 ：通过修改 /etc/resolvconf/resolv.conf.d/base（这个文件默认是空的）
sudo vi /etc/resolvconf/resolv.conf.d/base
在里面插入：
nameserver 202.97.224.68
nameserver 202.97.224.69
如果有多个DNS就一行一个
修改好保存，然后执行：
resolvconf -u
再看/etc/resolv.conf，最下面就多了2行：
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 202.97.224.68
nameserver 202.97.224.69
可以看到设置的多个DNS已经加上了，然后再ping一下百度，立即就可以解析了，无需重启。
