Thank you very much for providing the additional information. I can now
reproduce the issue in a stock ubuntu-24.04.1-live-server-amd64.iso
installation. => After "apt install ubuntu-desktop-minimal" the primary
ethernet interface is listed as "enp1s0 ethernet unmanaged --" by
NetworkManager ("nmcli d"), which is expected, as "netplan apply" was
not run, yet. BUT: It's also listed as unmanaged by systemd-networkd
("networkctl"), therefore dropped it's DNS configuration from
"resolvectl".
I think I've found an even smaller reproducer:
$ lxc launch ubuntu-daily:noble nn-lp2097769-desktop-dns
$ lxc shell nn-lp2097769-desktop-dns
root@nn-lp2097769-desktop-dns:~# networkctl
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
307 eth0 ether routable configured
11 links listed.
root@nn-lp2097769-desktop-dns:~# resolvectl
Global
Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub
Link 307 (eth0)
Current Scopes: DNS
Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 10.238.94.1
DNS Servers: 10.238.94.1 fd42:7213:f20e:bd74::1 fe80::216:3eff:fe0f:ee29
DNS Domain: lxd
root@nn-lp2097769-desktop-dns:~# apt install ubuntu-settings network-manager
[...]
# still OK
root@nn-lp2097769-desktop-dns:~# nmcli d
DEVICE TYPE STATE CONNECTION
eth0 ethernet connected (externally) eth0
lo loopback connected (externally) lo
root@nn-lp2097769-desktop-dns:~# networkctl
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
307 eth0 ether routable configured
root@nn-lp2097769-desktop-dns:~# resolvectl
Global
Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub
Link 307 (eth0)
Current Scopes: DNS
Protocols: +DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 10.238.94.1
DNS Servers: 10.238.94.1 fd42:7213:f20e:bd74::1 fe80::216:3eff:fe0f:ee29
DNS Domain: lxd
# but networkd config for eth0 already gone:
root@nn-lp2097769-desktop-dns:~# ls /run/systemd/network/
=> empty
# now restarting systemd-networkd.service leads to eth0 becoming unmanaged (as
the .network file is gone)
# and DNS config is dropped
root@nn-lp2097769-desktop-dns:~# systemctl restart systemd-networkd
root@nn-lp2097769-desktop-dns:~# networkctl
IDX LINK TYPE OPERATIONAL SETUP
1 lo loopback carrier unmanaged
307 eth0 ether routable unmanaged
root@nn-lp2097769-desktop-dns:~# resolvectl
Global
Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub
Link 307 (eth0)
Current Scopes: none
Protocols: -DefaultRoute -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
So the reporducer comes down to:
$ apt install ubuntu-settings network-manager && systemctl restart
systemd-networkd.service
=> ubuntu-settings installs /usr/lib/netplan/00-network-manager-all.yaml
("renderer: NetworkManager")
=> network-manager installation leads to "netplan generate" being executed by
the NM-Netplan integration
=> SOMETHING?? (during "apt install ubuntu-destkop-minimal") restarts
systemd-networkd.service, as can be seen from the logs of comment #18:
```
Feb 14 10:17:39 test24 systemd-networkd[839]: enp1s0: Configuring with
/run/systemd/network/10-netplan-enp1s0.network.
Feb 14 10:17:39 test24 systemd[1]: Started systemd-networkd.service - Network
Configuration.
Feb 14 10:17:39 test24 systemd-networkd[839]: enp1s0: DHCPv4 address
192.168.122.50/24, gateway 192.168.122.1 acquired from 192.168.122.1
Feb 14 10:20:57 test24 systemd[1]: Stopping systemd-networkd.service - Network
Configuration...
Feb 14 10:20:57 test24 systemd-networkd[839]: enp1s0: DHCPv6 lease lost
Feb 14 10:20:57 test24 systemd[1]: systemd-networkd.service: Deactivated
successfully.
Feb 14 10:20:57 test24 systemd[1]: Stopped systemd-networkd.service - Network
Configuration.
Feb 14 10:20:57 test24 systemd[1]: Starting systemd-networkd.service - Network
Configuration...
Feb 14 10:20:57 test24 systemd-networkd[14398]: lo: Link UP
Feb 14 10:20:57 test24 systemd-networkd[14398]: lo: Gained carrier
Feb 14 10:20:57 test24 systemd-networkd[14398]: enp1s0: Link UP
Feb 14 10:20:57 test24 systemd-networkd[14398]: enp1s0: Gained carrier
Feb 14 10:20:57 test24 systemd-networkd[14398]: enp1s0: Gained IPv6LL
Feb 14 10:20:57 test24 systemd-networkd[14398]: Enumeration completed
```
With those 3 circumstances coming together, we end up in a situation
where "netplan generate" already produced configuration for the new
setup, but "netplan apply" was not yet executed, enabling that new
configuration. But systemd-networkd.service gets restarted picking up
the new configuration already (outside of Netplan's control), therefore
both networking daemons now don't feel responsible to manage the
interface/DNS.
IMO this could be fixed in 3 different ways:
1/ not having "renderer: NetworkManager" in the netplan configuration # but we
actually want to have NM managing the network after a reboot.
2/ not calling "netplan generate" from NetworkManager (LP: #2090848)
3/ not restarting systemd-networkd.service during "apt install
ubuntu-desktop-minimal"
Whereas the simple workaround would be to execute:
$ netplan apply
=> This will put control for the interface in NetworkManager's hands, as
described in the Netplan configuration. DNS will be working again.
@enr0n, do you have any idea why systemd-networkd.service would be restarted
during "apt install ubuntu-desktop-minimal"?
** Changed in: systemd (Ubuntu)
Status: Incomplete => Confirmed
** Changed in: netplan.io (Ubuntu)
Status: New => Triaged
** Changed in: netplan.io (Ubuntu)
Importance: Undecided => Medium
** Tags added: server-triage-discuss
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https://bugs.launchpad.net/bugs/2097769
Title:
Installation of ubuntu-desktop-minimal breaks DNS
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