resolv.confが書き換わる

systemd-resolved が書き換えている

これに伴い /etc/resolv.conf の nameserver のデフォルト値が 127.0.0.53 になった

対策

sudo systemctl disable systemd-resolved.service

$ sudo apt update
$ sudo apt install resolvconf

vi /etc/resolvconf/resolv.conf.d/head

その中に次の行を追加します。

nameserver 8.8.8.8
nameserver 8.8.4.4

sudo systemctl start resolvconf.service

/etc/resolv.confファイルを確認する

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.
nameserver 8.8.8.8
nameserver 8.8.4.4

nameserver 127.0.0.53
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