[BUG] NixOS module shows blank screen, logs show X11 fallback

[sebadaba]

I'm migrating from noctalia v4 and wanted to try out noctalia-greeter (before I just used greetd with autologin). I added the input to my flake, and just added:

    imports = [
      inputs.noctalia-greeter.nixosModules.default
    ];

    programs.noctalia-greeter = {
      enable = true;
    };

to my config and removed my greetd config, because I understand that the noctalia-greeter module handles it all. It builds fine.

But when I reboot, I get a black screen. cat /var/lib/noctalia-greeter/greeter.log shows many identical entries:

=== noctalia-greeter-session 2026-07-07T20:04:39-04:00 pid=2501 uid=999 euid=999 ===
GREETER_BIN=/nix/store/17ffmf0whya5qhshd97s7bzmpv87ih9p-noctalia-greeter-1.0.0/bin/noctalia-greeter
COMPOSITOR_BIN=/nix/store/17ffmf0whya5qhshd97s7bzmpv87ih9p-noctalia-greeter-1.0.0/bin/noctalia-greeter-compositor
LOG_FILE=/var/lib/noctalia-greeter/greeter.log
GREETD_SOCK=/run/greetd-2490.sock
XDG_RUNTIME_DIR=/tmp/noctalia-runtime-999 (pam=/run/user/999)
WAYLAND_DISPLAY=unset
launch: /nix/store/17ffmf0whya5qhshd97s7bzmpv87ih9p-noctalia-greeter-1.0.0/bin/noctalia-greeter-compositor -- --
00:00:00.000 [INFO] [backend/x11/backend.c:394] Creating X11 backend
00:00:00.000 [ERROR] [backend/x11/backend.c:407] Failed to open xcb connection
failed to create wlroots backend

which I assume tries to "create the X11 backend" as a fallback because something else broke but I honestly have no idea what that could be.

Also, this is the log from greetd.service:

❯ journalctl -u greetd.service -b -1
Jul 07 20:04:31 nostromo systemd[1]: Started greetd.service.
Jul 07 20:04:37 nostromo greetd[2265]: pam_unix(greetd:session): session opened for user greeter(uid=999) by (uid=0)
Jul 07 20:04:37 nostromo greetd[2265]: gkr-pam: gnome-keyring-daemon started properly
Jul 07 20:04:37 nostromo greetd[2265]: pam_unix(greetd:session): session closed for user greeter
Jul 07 20:04:37 nostromo greetd[2044]: error: check_children: greeter exited without creating a session
Jul 07 20:04:37 nostromo systemd[1]: greetd.service: Deactivated successfully.
Jul 07 20:04:37 nostromo systemd[1]: greetd.service: Consumed 13ms CPU time over 6.327s wall clock time, 8.7M memory peak, 4.4M read from disk.
Jul 07 20:04:37 nostromo systemd[1]: greetd.service: Scheduled restart job, restart counter is at 1.

(...)

Jul 07 20:04:39 nostromo systemd[1]: Started greetd.service.
Jul 07 20:04:39 nostromo greetd[2491]: pam_unix(greetd:session): session opened for user greeter(uid=999) by (uid=0)
Jul 07 20:04:39 nostromo greetd[2491]: gkr-pam: gnome-keyring-daemon started properly
Jul 07 20:04:39 nostromo greetd[2491]: pam_unix(greetd:session): session closed for user greeter
Jul 07 20:04:39 nostromo greetd[2490]: error: check_children: greeter exited without creating a session
Jul 07 20:04:39 nostromo systemd[1]: greetd.service: Deactivated successfully.
Jul 07 20:04:39 nostromo systemd[1]: greetd.service: Scheduled restart job, restart counter is at 5.
Jul 07 20:04:39 nostromo systemd[1]: greetd.service: Start request repeated too quickly.
Jul 07 20:04:39 nostromo systemd[1]: greetd.service: Failed with result 'start-limit-hit'.
Jul 07 20:04:39 nostromo systemd[1]: Failed to start greetd.service.

Lastly, I'm using NixOS 26.05. If I'm doing something wrong or more information is needed please let me know.