1.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 127.0.0.53
options 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：
1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-resolved3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 8.8.8.8
nameserver 114.114.114.114
