前段时间，我偶然进行查看linux DNS配置，通过查看 /etc/resolv.conf 文件，得到如下结果：
➜ devices ll /etc/resolv.conf lrwxrwxrwx 1 root root 39 12月 28 18:55 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf ➜ devices cat /etc/resolv.conf # 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
之前，我曾经简单写过一个linux下如何获取dns服务器的博客：Linux 中查看 DNS 与 配置；但是无论怎么查找，显示的都是 127.0.0.53 回环地址。说明 ubuntu 对dns服务器做了一层管理，但是内部的机制我还不是很明白。所以今天进行简要了解一下，填一下年前遗留的一个坑。通过上述注释我们可以了解到，我们可以使用 resolvectl status 命令查看上行链路的dns服务器。我们也可以使用自己创建regular文件进行手动配置；命令运行情况如下：
这显然于我们在netplan中配置的dns相同：
但是，127.0.0.53 代表的是什么呢，其存在的必要性是什么呢？我对此进行了进一步探究，并进行简要记录，方便我个人记忆，如果对你也有启发，欢迎留言讨论：
- Resolved is a local, caching, DNS nameserver resolver and is used by default on Ubuntu.
- https://www.freedesktop.org/software/systemd/man/systemd-resolved.service.html (通过阅读此链接和多问题可得到答案)
- 关于配置文件，可以参考：/etc/systemd/resolved.conf
- 相关讲座：https://ftp.belnet.be/mirror/FOSDEM/2019/K.4.601/dns_systemd_resolved.webm
- systemd-resolved 带来的好处，一个是统一了dns的管理；另外一个就是可以通过本地cache加速dns查询；
参考文档：
How and why (not) to use the 127.0.0.53 nameserver, systemd-resolved and resolvctl