[Bug 2107575] Re: Offline install results in empty /etc/netplan, which stalls boot for 2min+

[Lukas Märdian]

IMO the root cause here is systemd-networkd-wait-online.service waiting
for any network interface to become "ready" by default. But with no
network interface connected/configured or even available (as described
in comment #2). It does not make sense to wait for anything.

I agree that adding some dummy Netplan config is probably a workaround to that symptom.
systemd upstream's stance is that sd-nd-wait-online.service should not be enabled if we do not want to wait for anything. But Ubuntu enables it by default.

Maybe the solution should be for subiquity to "systemctl disable/mask
systemd-networkd-wait-online.service" whenever it does not install any
network configuration in /etc/netplan/ ? That way we sould not run into
the timeout, while at the same time not placing any config in
/etc/netplan/.

The only drawback would be that users would need to manually re-enable
that service again if they configure their network interface afterward
and want to rely on the wait-online logic.

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https://bugs.launchpad.net/bugs/2107575

Title:
  Offline install results in empty /etc/netplan, which stalls boot for
  2min+

Status in subiquity:
  New
Status in systemd package in Ubuntu:
  New

Bug description:
  I did an offline install of plucky 25.04 server on a laptop. I
  unplugged the network cable, and didn't configure wifi.

  The installation finished, but first boot, and subsequent boots, were
  delayed by 2min+, waiting on systemd-networkd-wait-online.service.

  Further inspection showed that /etc/netplan was completely empty. Not
  surprising to me, as no network was configured during installation,
  but having the system still waiting for a network in this case was
  surprising.

  Creating the following file in /etc/netplan made boot fast again:

  $ cat /etc/netplan/01.yaml
  network:
    version: 2
    ethernets:
      <nic-name>:
        optional: true

  This looks similar to
  https://bugs.launchpad.net/subiquity/+bug/2063331, but I opted to file
  a new bug because that one is "fix committed", and the user did
  configure one nic at least in that bug.

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