Temporary failure in name resolution on Ubuntu server 22.04.3 LTS

[Bo Berglund]

On Sun, 26 Nov 2023 12:41:07 +0100, Bo Berglund <bo.berglund at gmail.com> wrote:

>On Sun, 26 Nov 2023 11:27:44 +0100, Oliver Grawert <ogra at ubuntu.com> wrote:
>****** HELP! ******
>
>How can I get the DNS working properly now?
>
>I have had to edit the hosts file to re-enable the specific setting for
>accessing my report server, but nothing else seems to work properly towards the
>Internet!
>
>To me it seems like the dist-upgrade from 20.04.6 LTS to 22.04.3 LTS back in
>october has broken the system in some strange way that has not shown up until a
>few days ago.
>This server started as a 16.04 and has been ugraded three times to the current
>state.
>

NOTES:
1) The server has been dist-upgraded several times and it has worked well
earlier. 16 -> 18 -> 20 -> 22

2) The references to NetworkManager in most of the web hits I have read
concerning the resolution to this problem do not work. For instance:
- nmcli does not exist
  $ nmcli
  Command 'nmcli' not found, but can be installed with:
  sudo snap install network-manager  # version 1.2.2-31, or
  sudo apt  install network-manager  # version 1.36.6-0ubuntu2
  See 'snap info network-manager' for additional versions.

- /etc/netplan/ is empty:
  $ ls -la /etc/netplan/
  total 16
  drwxr-xr-x   2 root root  4096 Aug 26  2019 .
  drwxr-xr-x 139 root root 12288 Nov 26 07:05 .

- I can see the state:
  ~$ resolvectl status
  Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
    resolv.conf mode: foreign
  Current DNS Server: 8.8.8.8
        DNS Servers: 8.8.8.8 8.8.4.4
        DNS Domain: DOMAINS

  Link 2 (eth0)
  Current Scopes: none
     Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
     DNS Domain: DOMAINS

  - But as soon as I have rebooted the DNS servers disappear.

3) I believe (but that is me) NetworkManager is NOT the manager for networks but
instead a migrated version of whatever was used earlier is now broken but
remains active. See item #2 above.

What can I do in order to fix the server?

This server is about 6500 km away and can be reached by me only via OpenVPN (it
is the OpenVPN server so is important). It only has a cli interface via SSH.

Grateful for a solution to this problem, which seems to have been caused by the
dist-upgrade...


-- 
Bo Berglund
Developer in Sweden