Polkit

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Polkit is used for controlling system-wide privileges. It provides an organized way for non-privileged processes to communicate with privileged ones. In contrast to sudo, it does not grant root permission to an entire process, but rather allows a finer level of control of centralized system policy.

Enable polkit

Polkit is disabled by default. If you wish to enable it, you can set security.polkit.enable to true.

Reboot/poweroff for unprivileged users

With the following rule, we can grant the permissions reboot and poweroff a machine to users in the users group.

This is useful on a multi-user machine. It may also be of particular importance when using XRDP or other similar Remote Desktop solutions.

/etc/nixos/configuration.nix

  security.polkit.extraConfig = ''
    polkit.addRule(function(action, subject) {
      if (
        subject.isInGroup("users")
          && (
            action.id == "org.freedesktop.login1.reboot" ||
            action.id == "org.freedesktop.login1.reboot-multiple-sessions" ||
            action.id == "org.freedesktop.login1.power-off" ||
            action.id == "org.freedesktop.login1.power-off-multiple-sessions"
          )
        )
      {
        return polkit.Result.YES;
      }
    });
  '';

(The above is a PolKit rule in JavaScript format. See https://www.freedesktop.org/software/polkit/docs/latest/polkit.8.html#polkit-rules for more information on the language.)

Authentication agents

If Polkit seems not to work properly, you could check that you have an authentication agent installed and running (especially if you use a more niche desktop environment like e.g. i3wm).

For example, polkit_gnome is a GNOME-based authentication agent, but it will usually only autostart when used with GNOME, KDE, or Unity (examine its autostart file in etc/xdg/autostart/polkit-gnome-authentication-agent-1.desktop for details); otherwise you will need to start it yourself, e.g. by copying that autostart file to ~/.config/autostart/ and removing the parts that restrict it to GNOME/KDE/Unity.

Alternatively, you can start it on login by creating a systemd user service:

systemd = {
  user.services.polkit-gnome-authentication-agent-1 = {
    description = "polkit-gnome-authentication-agent-1";
    wantedBy = [ "graphical-session.target" ];
    wants = [ "graphical-session.target" ];
    after = [ "graphical-session.target" ];
    serviceConfig = {
        Type = "simple";
        ExecStart = "${pkgs.polkit_gnome}/libexec/polkit-gnome-authentication-agent-1";
        Restart = "on-failure";
        RestartSec = 1;
        TimeoutStopSec = 10;
      };
  };
};

Another option is lxqt.lxqt-policykit, which can be launched on login through the command lxqt-policykit-agent on e.g. Hyprland.

Start the authentication agent in dwm

If you use dwm patched with dwm-autostart-20210120-cb3f58a.diff, you can add a command into ~/.dwm/autostart.sh to start a polkit agent. Here take mate.mate-polkit for example:

#!/bin/sh
# General stuff
...
/nix/store/$(ls -la /nix/store | grep 'mate-polkit' | grep '4096' | awk '{print $9}' | sed -n '$p')/libexec/polkit-mate-authentication-agent-1 & 
...

Use this method, you won't need to change the codes even mate.mate-polkit gets an update.

#!/bin/sh
...
/nix/store/$(ls -la /nix/store | grep polkit-kde-agent | grep '^d' | awk '{print $9}')/libexec/polkit-kde-authentication-agent-1 & 
...

The same but for polkit-kde-agent