众所周知：
Ubuntu在域名解析时，最直接使用的是/etc/resolve.conf文件，它是/run/systemd/resolve/
resolve.conf的软链接，而对于刚装完的ubuntu系统，该文件的内容如下：
# This file is managed by man:systemd-resolved(8). Do not edit.## This is a dynamic resolv.conf file for connecting local clients to the# internal DNS stub resolver of systemd-resolved. This file lists all# configured search domains.## Run "resolvectl status" to see details about the uplink DNS servers# currently in use.## Third party programs must not access this file directly, but only through the# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,# replace this symlink by a static file or a different symlink.## See man:systemd-resolved.service(8) for details about the supported modes of# operation for /etc/resolv.conf.nameserver 127.0.0.53options edns0 trust-ad问题分析：
很显然，我们需要做的就是在/etc/resolve.conf中，配置我们需要的域名解析服务器地址，例如：“nameserver 8.8.8.8”，但是这个文件即使我们修改了，很快又会被覆盖，而且我们注意一个细节——文件的开头就注明了“Do not edit”，到了这里，我们就应该反应过来，直接修改/etc/resolve.conf是不正确的。
解决方案：
第1步， 修改/etc/systemd/resolved.conf，例如：
# This file is part of systemd.## systemd is free software; you can redistribute it and/or modify it# under the terms of the GNU Lesser General Public License as published by# the Free Software Foundation; either version 2.1 of the License, or# (at your option) any later version.## Entries in this file show the compile time defaults.# You can change settings by editing this file.# Defaults can be restored by simply deleting this file.## See resolved.conf(5) for details[Resolve]DNS=8.8.8.8 114.114.114.114#FallbackDNS=#Domains=#LLMNR=no#MulticastDNS=no#DNSSEC=no#DNSOverTLS=no#Cache=no-negative#DNSStubListener=yes#ReadEtcHosts=yes个人猜测，这个时候，系统在往/run/systemd/resolve/resolv.conf里面写域名解析服务器地址的时候，会从/etc/systemd/resolved.conf中取得DNS相关的配置。
2，重启域名解析服务
systemctl restart systemd-resolved
systemctl enable systemd-resolved
3，备份当前的/etc/resolve.conf，并重新设置/run/systemd/resolve/resolv.conf 到/etc/resolve.conf的软链接
mv /etc/resolv.conf /etc/resolv.conf.bak
ln -s /run/systemd/resolve/resolv.conf /etc/
验证成果：
# This file is managed by man:systemd-resolved(8). Do not edit.## This is a dynamic resolv.conf file for connecting local clients directly to# all known uplink DNS servers. This file lists all configured search domains.## Third party programs must not access this file directly, but only through the# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,# replace this symlink by a static file or a different symlink.## See man:systemd-resolved.service(8) for details about the supported modes of# operation for /etc/resolv.conf.nameserver 8.8.8.8nameserver 114.114.114.114感谢各个论坛大佬的分享，主要参考：
https://www.cnblogs.com/mouseleo/p/14976527.html