Netplan generator causes systemd, apt and unlock hangs on 24.04

[Florian Hackenberger]

From the issue in the netplan tracker [1]:

During a systemd daemon-reload, the Netplan generator in /usr/lib/systemd/system-generators/netplan tries to reload the udev rules and databases with udevadm control --reload [2], which causes a deadlock, because reloading udev rules and databases requires a functioning systemd-userdbd.service, which is not the case during a systemd daemon-reload. The systemd developers will not consider making changes to any systemd component in order to prevent this deadlock, and instead suggest that the Netplan developers generate their systemd link/network/netdev units using a generator service like systemd-network-generator.service.

[1] https://bugs.launchpad.net/netplan/+bug/1999178

On my machine, this causes every 'apt install' to be very slow, enabled / disabling systemd services to be slow, sudo hanging while these processes hang and so on.

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: netplan-generator 1.0-2ubuntu1
ProcVersionSignature: Ubuntu 6.5.0-35.35-generic 6.5.13
Uname: Linux 6.5.0-35-generic x86_64
ApportVersion: 2.28.1-0ubuntu3
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: GNOME
Date: Sat Jun 15 12:33:39 2024
InstallationDate: Installed on 2023-09-21 (268 days ago)
InstallationMedia: Ubuntu 23.04 "Lunar Lobster" - Release amd64 (20230417)
SourcePackage: netplan.io
UpgradeStatus: Upgraded to noble on 2024-05-28 (18 days ago)

[Florian Hackenberger (f-hackenberger)]

Oh fixing this also solved 60 seconds+ hangs when unlocking my desktop after resuming from suspend.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Ilya Loginov (isloginov)]

I tried to investigate the problem with long boot for several days. Even tried to reinstall system.

Only after enabling debug logs in systemd I found out that it was `/usr/lib/systemd/system-generators/netplan`. systemd-analyze told it was NetworkManager.

So I removed link `/usr/lib/systemd/system-generators/netplan` and my boot time reduced for almost 2mins.

There was nothing interesting in `/etc/netplan/01-network-manager-all.yaml` (with 0400 access rights, that was strange):
```
network:
  version: 2
  renderer: NetworkManager
```

[Martin Damzog (thessalonians)]

I can reproduce this bug by typing 'sudo netplan --debug generate' in the shell. This netplan command takes about 1 min to complete. On sound systems, it will only take one second. Deleting the link – as described by Ilya – solves the problem.

[Lukas Märdian (slyon)]

Thanks for reporting this issue! I'm marking this as a duplicate of bug #1999178

Let's try to keep the discussion in one place.