Weird 'gdm-greeter-N' warnings since `nix flake update`

1

I get a weird warning of not applying an UID change of the users gdm-greeter-N:

# nixos-rebuild test
building the system configuration...
Checking switch inhibitors... done
stopping the following units: accounts-daemon.service, systemd-tmpfiles-resetup.service
activating the configuration...
warning: not applying UID change of user ‘gdm-greeter-2’ (60580 -> 60579) in /etc/passwd
warning: not applying UID change of user ‘gdm-greeter-3’ (60581 -> 60580) in /etc/passwd
warning: not applying UID change of user ‘gdm-greeter-4’ (60582 -> 60581) in /etc/passwd
removing user ‘gdm-greeter-1’
setting up /etc...
reloading user units for johannes...
reloading the following user units: dbus-broker.service
restarting sysinit-reactivation.target
reloading the following units: dbus-broker.service
restarting the following units: polkit.service
starting the following units: accounts-daemon.service, systemd-tmpfiles-resetup.service
the following new units were started: NetworkManager-dispatcher.service
Done. The new configuration is /nix/store/p2zz15dcghcx66s92rw064mdjmrl9bh7-nixos-system-johannes-pc-26.05.20260523.64c08a7

To track the warning down I have performed a git bisect of my configuration and the issue was introduced by this bad ‘nix flake update’ commit. Keep in mind, I am on nixos-unstable. I believe the issue is likely to affect nixos-26.05 too (Edit: probably not).

I expect nixos-rebuild should run without such warnings.

2

I have investigated this further and it is likely introduced by one of this four commits:

[johannes@johannes-pc:~/src/nixpkgs]$ git log 29916453413845e54a65b8a1cf996842300cd299..64c08a7ca051951c8eae34e3e3cb1e202fe36786 | grep -a4 nixos/gdm
Merge: 63eca7de11f0 82ed78a9ee81
Author: Bobby Rong <rjl931189261@126.com>
Date:   Sat May 23 15:16:06 2026 +0000

    nixos/gdm: update `gdm-greeter` user homes, add warning for pulseaudio (#521789)

commit 63eca7de11f012e165194fa74a6cc2065a29a5b4
Merge: 3fd33038d11b 0f345cc540b1
Author: jopejoe1 <nixpkgs@missing.ninja>
--
commit 82ed78a9ee81eada31b619ebcdbb248daa123b9a
Author: winston <hey@winston.sh>
Date:   Thu May 21 03:00:07 2026 +0200

    nixos/gdm: add warning for Pulseaudio + gdm

    We plan to use systemd-userdbd for NixOS 26.11, which will dynamically
    allocate greeter users + their homes, which would break the current PA
    config. GNOME already depends on PipeWire in other places, so there's
--
commit 3fb5cf873d8eab026954ca596e4e662fb96efbd8
Author: winston <hey@winston.sh>
Date:   Tue May 19 04:15:50 2026 +0200

    nixos/gdm: update `gdm-greeter` user homes

    This fixes gdm not being able to save config changes made on the log-in
    screen, such as turning on accessibility options. The new values for the
    `gdm-greeter{-2,-3,-4,-5}` users map onto what userdbd would create for us.
--
commit bb23a160a1da7fc90f5e22b5e59d4cc1d7ad153e
Author: winston <hey@winston.sh>
Date:   Tue May 19 03:51:49 2026 +0200

    Revert "nixos/gdm: fix greeter permissions"

    This reverts commit 13759bea6c03703470e59213004e06c22819e7fc.

I am interested in any GDM user on unstable or 26.05-beta. Are you encountering this issue, too?

3

First commit is the merge commit for the third commit.

They manually set the uid for the greeter users, maybe you can ask on that PR why - it seems to be off-by-one, so it could be an error.

4

Thanks for your investigation. Yes, I guessed that it is related to this commit.

PS I am still interested if other users encountered this. In particular, if 26.05 is affected, too.

5

I have created an issue report nixos/gdm: UID mismatch of gdm-greeter-* users due to update · Issue #525919 · NixOS/nixpkgs · GitHub