ubuntu18.04清除自带systemd-resolved服务

### 报错： 53端口被占用

#停止
systemctl stop systemd-resolved
# 不设置自启动
systemctl disable systemd-resolved
# 重新写入dns配置
echo -e "nameserver 114.114.114.114" > /etc/resolv.conf
#修改nsswitch（不修改无法链接外网）
vi /etc/nsswitch.conf
修改 hosts 为 
hosts: files dns mymachines