ubuntu18 自带dns服务systemd-resolved

停掉自带的dns管理服务

systemctl stop systemd-resolved
systemctl disable systemd-resolved

删除dns配置文件

rm /etc/resolv.conf

重新写入dns解析

echo -e "nameserver 114.114.114.114" > /etc/resolv.conf

修改/etc/nsswitch.conf

这个文件不修改，无法连接外网

vi /etc/nsswitch.conf
修改 hosts 为 
hosts: files dns mymachines