Ubuntu Desktop 22.04の名前解決の設定を確認する！

Ubuntu Desktop 22.04の名前解決の設定を確認します。

systemd-resolved.serviceの状態を確認する！

systemd-resolved.serviceが起動していることを確認します。

$ systemctl status systemd-resolved.service
● systemd-resolved.service - Network Name Resolution
     Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
     Active: active (running) since Sat 2022-12-10 14:39:12 JST; 4h 11min ago
       Docs: man:systemd-resolved.service(8)
             man:org.freedesktop.resolve1(5)
             https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
             https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
   Main PID: 645 (systemd-resolve)
     Status: "Processing requests..."
      Tasks: 1 (limit: 18976)
     Memory: 8.9M
        CPU: 158ms
     CGroup: /system.slice/systemd-resolved.service
             └─645 /lib/systemd/systemd-resolved

Dec 10 14:39:11 dpc011p1 systemd[1]: Starting Network Name Resolution...
Dec 10 14:39:12 dpc011p1 systemd-resolved[645]: Positive Trust Anchors:
Dec 10 14:39:12 dpc011p1 systemd-resolved[645]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Dec 10 14:39:12 dpc011p1 systemd-resolved[645]: Negative trust anchors: home.arpa 10.in-addr.arpa 16.172.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.172.in-addr.arpa 21.172.in-addr.arpa 22>
Dec 10 14:39:12 dpc011p1 systemd-resolved[645]: Using system hostname 'dpc011p1'.
Dec 10 14:39:12 dpc011p1 systemd[1]: Started Network Name Resolution.
Dec 10 14:39:16 dpc011p1 systemd-resolved[645]: eno1: Bus client set default route setting: yes
Dec 10 14:39:16 dpc011p1 systemd-resolved[645]: eno1: Bus client set DNS server list to: 10.1.20.1, 10.1.0.1
Dec 10 14:39:39 dpc011p1 systemd-resolved[645]: Clock change detected. Flushing caches.

名前解決の設定を確認する！

名前解決の設定を確認します。resolv.confは、以下固定で実際の設定がされているわけではありません。

$ cat /etc/resolv.conf
# This is /run/systemd/resolve/stub-resolv.conf managed by man:systemd-resolved(8).
# Do not edit.
#
# This file might be symlinked as /etc/resolv.conf. If you're looking at
# /etc/resolv.conf and seeing this text, you have followed the symlink.
#
# 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 should typically 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
search .

実際の設定は、以下を確認します。GUIで設定した値が、確認できるはずです。生成された設定ファイルなので、こちらで編集することはしないようにしましょう。

$ cat /run/systemd/resolve/resolv.conf
# This is /run/systemd/resolve/resolv.conf managed by man:systemd-resolved(8).
# Do not edit.
#
# This file might be symlinked as /etc/resolv.conf. If you're looking at
# /etc/resolv.conf and seeing this text, you have followed the symlink.
#
# 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 should typically 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 10.1.20.1
nameserver 10.1.0.1
search .

おわりに

DNSリゾルバの設定は、もはや「/etc/resolv.conf」ではないことに注意しましょう。

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