Change:
systemd.packages = with pkgs.gnome; [ gdm gnome-session gnome-shell ]; environment.systemPackages = [ pkgs.gnome.adwaita-icon-theme ]; <ins> # We dont use the upstream gdm service # it has to be disabled since the gdm package has it # https://github.com/NixOS/nixpkgs/issues/108672 systemd.services.gdm.enable = false; </ins> systemd.services.display-manager.wants = [ # Because sd_login_monitor_new requires /run/systemd/machines "systemd-machined.service"

Discussion:
Describe the bug I updated my system (unstable) channel and now refuses to start: To Reproduce The important parts of my configuration (I hope this is enough to reproduce): I was previously on nixpkgs commit (something from september 2020), and updated to latest unstable as of 2021-01-06 (cannot easily copy commit atm, maybe ). Expected behavior Gdm starts just fine, just as it did before. Notify maintainers Gnome team: Metadata system: host os: multi-user?: sandbox: version: Maintainer information:
Could it be related that my gnome-wayland session does not show up?
I forgot to add this, outputs . If your Gnome-session does not show up, run that command to see if you get the same error message. Also, it seems like the bug is not 100% deterministic: when rebooting often enough, it will work sometimes. So I suppose that there is some race hazard between two services owning that dbus name. Maybe I'll try looking at the session to find out which service took the name.
no I do not, so probably my issue is not related. Still we could also compare (I have = true) Where I think for me there are a few interesting lines, the ones related to wayland (I do not get why I am not seeing a wayland session) but I don't see any particularly interesting ones and and similar
I have the same error. I booted into an older generation gdm worked fine (could be a lucky reboot or the older generation is fine :shrug:) but when I'm in i3 running I still see that error. Slightly trimmed config:
Okay, I just found that a gdm process is already running (supposedly outside of systemd?!). Killing it will boot up my GUI. However, the systemd unit stays broken no matter what I do. It will always say the unit's not started and that it can't start it due to the bus name collision. Even after killing everything including dbus itself, the error is the same. Very weird.
I have the same issue plus I have couple of problems. Even if I use open-source nvidia driver gdm doesn't show me wayland. Also nvidia-prime doesn't work for me.

I think the only way to make progress on this issue if someone goes ahead and bisects it. And I probably won't do it because I reverted back to Arch Linux for now and don't have any non-headless NixOS machines anymore.
I can try to help and also think it might be related to some issues with pam on nixos-unstable or related to flakes. I think this because when I tried to increase the file descriptors limit with still reports 1024. But I am not sure what else could be done to bisect it (relatively new to nix). EDIT: I am now sure that I probably face another issue disabling gives me the option to login the wayland session.
The best way for bisecting it would be to write a test that triggers the issue. should be a good starting point. Then, on the test file to bisect it. However, I haven't managed to find a configuration that reproduces it in the VM. Maybe it isn't event reproducible at all this way.
I'm hitting this same issue. It looks like gdm-wayland-session fails to start, and then it starts a gnome x session which fails because of some duplication. has the part of journalctl where wayland fails.
I can log in with a low-resolution graphical display if I change the displayManager from to .
I was able to solve my issue with For reference, I have a R7 360 graphics card.
I had the same problem I removed these options:-
This affects me too, on every boot runs gdm ok.
Getting hit by this now and again on 21.05. So far it's always worked on boot, but the gui crashes every few hours. Thanks for the temp fix of killing the other instance of gdm. Looking in journalctl: Some other configs:
I almost never experience the issue where gdm doesn't start at all, but even when it's running and everything is OK, I see in the error: Indeed both systemd files and have the deriviative: And we do add both of them with: And: Where brings the derivative from the source package. I think it should be fairly easy to remove the derivative from one of the services, even from - although it's from a package. I don't know how to decide which to remove, from seems redundant compared to upstream's .