
It was lacking the dbus configuration to bind to org.freedesktop.DisplayManager, and it was passing fixed TTY/display numbers to the X server (see 9be012f0d4d9b6bca35416ec89d5a40be4556896).
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at http://nixos.org/nixos and in the manual in doc/manual.