默认安装好ubuntu server 22.04LTS后，系统使用systemd-resolved 53端口端口的dns服务为本机提供服务。

Ubuntu的systemd-resolved将默认监听在53号端口，如果我们需要运行自己定义的dns服务器，端口已经在使用会导致端口冲突。所以我们会遇见下面的错误：

"listen tcp 0.0.0.0:53: bind: address already in use".

查看端口情况

root@sunday:~# netstat -lnpt|grep 53
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      2119/systemd-resolv

或者

root@sunday:~# sudo lsof -i :53
COMMAND    PID            USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
systemd-r 2119 systemd-resolve   12u  IPv4  67939      0t0  UDP localhost:domain
systemd-r 2119 systemd-resolve   13u  IPv4  67940      0t0  TCP localhost:domain (LISTEN)

如何停止ubuntu上的systemd-resolved服务使用53

1.修改配置文件

修改/etc/systemd/resolved.conf中DNSStubListener的注释行，它将不再打开dns服务

root@sunday:~# cat /etc/systemd/resolved.conf
#  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=
#FallbackDNS=
#Domains=
#LLMNR=no
#MulticastDNS=no
#DNSSEC=no
#DNSOverTLS=no
#Cache=no-negative
#DNSStubListener=yes  将这行的注释拿掉,改为no保存，如下
DNSStubListener=no  
#ReadEtcHosts=yes

2.创建链接

将下面的文件创建一个软链接到etc文件夹下

sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf

3.生效配置

systemctl restart systemd-resolved.service

检查53是否使用：

lsof -i :53

批量脚本

sed -i 's/^#\?DNSStubListener=.*/DNSStubListener=no/' /etc/systemd/resolved.conf
ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
systemctl restart systemd-resolved.service