Comment 12 for bug 1931088

So I can reproduce the problem even locally, using a simple:
`autopkgtest systemd --test-name=boot-and-services -- lxd autopkgtest/ubuntu/impish/amd64`

When logging into the (stalled) system, while it is waiting for its timeout I can see that eth0 gets configured, but then put in DOWN state. Therefore, systemd-networkd-wait-online.service (and thus network-wait-online.target) never get ready and the test times out waiting on "network-wait-online.target".

A simple "networkctl up eth0" (inside the LXD container) during that 60s "timeout-wait" makes the test runner connect an finish the test successfully.

The culprit for bringing down the interface seems to be "/run/systemd/system/network-device-down.service", but I have no idea where this files comes from or what it is used for. It's not part of any package.

That service has a "Before=NetworkManager.service" dependency, that's why it only breaks tests making use of network-manager (boot-and-services & boot-smoke).

The LXD/LXC stack seems to be somehow involved in creating that file: https://github.com/lxc/lxc-ci/pull/266