Scary message about "dbus" after running "nixos-rebuild switch"

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1

Basically, I ran into the same issue described here: "Switching into this system is not recommended" message due to dbus implementation change · Issue #1039 · nix-community/NixOS-WSL · GitHub

I got this message after running nixos-rebuild switch:

Checking switch inhibitors...
There are changes to critical components of the system:

dbus-implementation : dbus -> broker

Switching into this system is not recommended.
You probably want to run 'nixos-rebuild boot' and reboot your system instead.

If you really want to switch into this configuration directly, then
you can set NIXOS_NO_CHECK=1 to ignore pre-switch checks.

WARNING: doing so might cause the switch to fail or your system to become unstable.

Well, I did what I was told; I ran nixos-rebuild boot and rebooted, and so far, I seem to be okay, but what happened here? And should I expect some further trouble?

Can we have some kind of forum PSA channel?
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nixos-rebuild boot is probably safe here.

The issue is stopping dbus.service on a live system which closes a lot of sockets, these sockets might not reconnect after the new dbus implementation is started leaving you with services disconnected from the bus.

By running nixos-rebuild boot and rebooting your computer, you are (among other things) stopping all affected services and starting them after the new dbus implementation has started.

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3

I’m guessing that explains the other issue I found when I Googled the scary message: Kernal: USB HID fails to be recognized after bootloader loads · Issue #513399 · NixOS/nixpkgs · GitHub

The reporter of that issue had problems with the USB keyboard not working after a reboot, which I expect could happen if a big change with dbus happened. I’m guessing that they didn’t run nixos-rebuild boot before they first rebooted.

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No, that’s completely unrelated.

The scary message isn’t intended to be scary, it’s just a new NixOS feature to prevent you breaking a running system by using the wrong command for updates.

In general, when you update, you should prefer the boot variant and a reboot, since you might be updating services (or the kernel) in ways that make other applications or services no longer compatible, causing issues.

A reboot will always fix the problems this warning is about, but e.g. you might have unsaved data and not want to reboot. Or you might be one of those people who only ever put their devices to sleep and come complaining about a bug that isn’t actually a bug because you haven’t rebooted after a dbus update.

I’d still recommend using boot even if you don’t get a scary message, because it’s unlikely this feature will be exhaustive, it relies on nixpkgs contributors correctly labeling their services. But it’s clearly teaching a number of people an important lesson.

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