systemd-resolved fails: Failed to start query: Invalid argument

[Matthias Nagel]

# lsb_release -rd
No LSB modules are available.
Description: Ubuntu 23.10
Release: 23.10

# aptitude show 'systemd-resolved'
Package: systemd-resolved
Version: 253.5-1ubuntu6
State: installed

The system is unable to resolve any DNS names. Whenever a DNS name shall be resolved the following error appears in the journal

Oct 21 15:50:32 my-host.my-domain.tld systemd-resolved[114]: Failed to start query: Invalid argument

If one manually tries to resolve a DNS name from the local stub resolver via

dig @127.0.0.53 A www.google.com.

another error message is added to the journal. However, resolving a DNS name from the configured upstream DNS server works perfectly

dig @81.169.163.106 A www.google.com.

Returns a proper response. (Note, 81.169.163.106 is the internal DNS server from my hoster.)

Some more infos

# resolvectl
Global
         Protocols: -LLMNR mDNS=resolve -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: stub
Current DNS Server: 81.169.163.106
       DNS Servers: 81.169.163.106 85.214.7.22
        DNS Domain: my-domain.tld

Link 2 (venet0)
    Current Scopes: none
         Protocols: -DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported

# cat /etc/systemd/resolved.conf

[Resolve]
DNS=81.169.163.106 85.214.7.22
Domains=my-domain.tld

# aptitude search '~i resolv'
i libnss-resolve - nss module to resolve names via systemd-resolved
i A systemd-resolved - systemd DNS resolver

[Matthias Nagel (nagmat84)]

Maybe related to #2040051.

[Nick Rosbrook (enr0n)]

Please provide debug-level logs from systemd-resolved.service from a time where this issue is observed. You can enable debug-level logging like this:

$ mkdir -p /etc/systemd/system/systemd-resolved.service.d/
$ cat > /etc/systemd/system/systemd-resolved.service.d/debug.conf << EOF
[Service]
Environment=SYSTEMD_LOG_LEVEL=debug
EOF
$ systemctl daemon-reload
$ systemctl restart systemd-resolved.service (or reboot if you prefer).

[Matthias Nagel (nagmat84)]

Unfortunately, increasing the log level to debug doesn't make any difference. I already tried the approach with the drop-in configuration file, but systemd-resolved doesn't log any additional information.

It is basically the same "non-reaction" as in https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/2040051/comments/3. Sorry, that I didn't mention that I already had tried to turn on debugging in the first place.