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.
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?
We have. After upgrading to 26.05, upgrade builds consistently end with
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
setting up /etc...
...
I’d like to make the appropriate changes, but one look at the current state and I decided to leave it for an upstream fix.
$ id gdm-greeter{,-{1..6}}
uid=60578(gdm-greeter) gid=132(gdm) groups=132(gdm)
id: ‘gdm-greeter-1’: no such user
uid=60580(gdm-greeter-2) gid=132(gdm) groups=132(gdm)
uid=60581(gdm-greeter-3) gid=132(gdm) groups=132(gdm)
uid=60582(gdm-greeter-4) gid=132(gdm) groups=132(gdm)
uid=60582(gdm-greeter-4) gid=132(gdm) groups=132(gdm)
id: ‘gdm-greeter-6’: no such user
In case you think I messed up a copy-n-paste there, I did not.
$ id gdm-greeter-5
uid=60582(gdm-greeter-4) gid=132(gdm) groups=132(gdm)
Currently on NixOS 26.11pre, using the nixos-unstable channel.
building the system configuration...
Checking switch inhibitors... done
updating GRUB 2 menu...
Warning: os-prober will be executed to detect other bootable partitions.
Its output will be used to detect bootable binaries on them and create new boot entries.
lsblk: /dev/mapper/no*[0-9]: No such file or directory
lsblk: /dev/mapper/raid*[0-9]: No such file or directory
lsblk: /dev/mapper/disks*[0-9]: No such file or directory
Found Windows 11 on /dev/sda1
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
setting up /etc...
reloading user units for greyhound...
restarting the following user units: nixos-activation.service
restarting sysinit-reactivation.target
the following new units were started: mandb.service, NetworkManager-dispatcher.service, sysinit-reactivation.target, systemd-tmpfiles-resetup.service
Done. The new configuration is /nix/store/dhp7i7cm6zcpqnih3mpqghf9rvdc06yx-nixos-system-nixos-26.11pre1040357.e2587caef70c
It is quite unfortunate this bug entered the stable 26.05 release. This makes it basically impossible to fix reliable. More details are in the linked issue.
A possible workaround is:
Disable GDM in your configuration
`nixos-rebuild boot` and reboot
(Typically LightDM shows up, but maybe you have to login via TTY)
Revert step 1
Repeat step 2
This effectively removes the GDM users and recreates them with the new UIDs.