{
  systemConfiguration = { config, ... }: {
    isNormalUser = true;
    # TODO: Don't hard-code `persist`.  Use
    # config.sydnix.impermanence.persistGroupName.
    extraGroups = [
      "wheel"
      "persist"
      "input"
      "dots"
      "greeter"
      "networkmanager"
    ];
    initialHashedPassword =
      "$y$j9T$4pyDiPlhnN4UarQoY7Sn70$URZQKPJ3yU4WoQFHRhzm4uF3bM4U7OVYem3oPioykMC";

    openssh.authorizedKeys.keyFiles = [
    ];
  };

  homeConfiguration = { config, lib, pkgs, host, ... }:
    let on = hosts:
          if builtins.isString hosts
          then hosts == host
          else builtins.elem host hosts;
    in {
      home.file.".ssh/id_ed25519".source =
        config.lib.file.mkOutOfStoreSymlink
          "/persist/private-keys/ssh/msyds@sydpc";

      home.file.".face".source = ./avatar.jpg;

      home.file.".ssh/id_ed25519.pub".source =
        ../../public-keys/ssh/${"msyds@sydpc.pub"};

      sydnix = {
        documentation.enable = true;
        xdg.enable = true;
        steam.enable = on "sydpc";
        zotero.enable = true;
        slippi.enable = on "sydpc";
        desktop-environment.enable = true;
        clojure.enable = true;
        capitaine-cursors.enable = true;
        terraria.enable = on "sydpc";
        kdeconnect.enable = true;
        qalculate.enable = true;
        toki-pona.enable = true;
        prism-launcher.enable = on "sydpc";
        flatpak.enable = on "sydpc";
        sops = {
          enable = true;
          keyFile = "/persist/private-keys/age/crumb";
        };
        # Personal configurations.
        users.crumb = {
          direnv.enable = true;
          git.enable = true;
          nvim.enable = true;
          readline.enable = true;
          niri.enable = true;
          firefox.enable = true;
          ghostty.enable = true;
          # waybar.enable = true;
          tf2.enable = true;
          fcitx5.enable = true;
          anki.enable = true;
          mumble.enable = true;
        };
        users.msyds = {
	  discord.enable = true;
          bash.enable = true;
          hunspell.enable = true;
          emacs.enable = true;
          impermanence.enable = true;
          syncthing.enable = true;
          fonts.enable = true;
	  dank-material-shell.enable = true;
	  sioyek.enable = true;
        };
      };

      # Don't touch!
      home.stateVersion = "18.09";
    };
}