Bare with me, this posts covers a solution that may partially work for some but will probably cause some trouble down the road. I’ll get to it in a minute. I’m a XMonad user, so I ended up relying on a solution that

Trying actkbd

Inside your configuration.nix, or whichever file you import from your configuration.nix with the purpose of containing audio-related settings, add the following snippet:

services.actkbd = with pkgs; {
  enable = true;
  bindings = [
    # "Mute" media key
    {
      keys = [ 113 ];
      events = [ "key" ];
      command = "${alsaUtils}/bin/amixer -q set Master toggle";
    }

    # "Lower Volume" media key
    {
      keys = [ 114 ];
      events = [ "key" "rep" ];
      command = "${alsaUtils}/bin/amixer -q set Master 1- unmute";
    }

    # "Raise Volume" media key
    {
      keys = [ 115 ];
      events = [ "key" "rep" ];
      command = "${alsaUtils}/bin/amixer -q set Master 1+ unmute";
    }
  ];
};

The keycodes for the snippet have been acquired by switching to a virtual terminal and running showkey. The showkey application displays the keycodes for the pressed keys and exits after 10 seconds without input. In my case the keycodes for mute, volume down and volume up represented the keycodes 113, 114 and 115 respectively.

Since my function keys have been configured in my BIOS to behave as function keys instead of multimedia keys, I can switch between virtual terminals by simultaneously pressing Ctrl, Alt and any of my function keys ranging from F1 through F12.

Triggering the multimedia behavior for mute, which is set up on the F1 key, will require me to simultaneously press Fn and F1. Note that Fn indicates to the system that I intent to trigger the alternate behavior for the given key.

The problem with this approach is that the actkbd daemon executes commands as root. Since the PulseAudio server imposes restrictions on who may connect to it, we need to connect as the same user as the one running the server.

XDG_RUNTIME_DIR (/run/user/1988) is not owned by us (uid 0), but by uid 1988! (This could e g happen if you try to connect to a non-root PulseAudio as a root user, over the native protocol. Don't do that.)

ALSA lib pulse.c:243:(pulse_connect) PulseAudio: Unable to connect: Connection refused

amixer: Mixer attach default error: Connection refused

XMonad

Retrieve the keysym for the required buttons in xev (0x1008ff12, 0x1008ff11 and 0x1008ff13 in my case) and add these to the xmonad.hs.

I’ve chosen to define my audio keys as a seperate list

audioKeys = [
    ((0, 0x1008ff12), spawn "amixer -q set Master toggle")
  , ((0, 0x1008ff11), spawn "amixer -q set Master 10%-")
  , ((0, 0x1008ff13), spawn "amixer -q set Master 10%+")
  ]

and concatenate them to the other bindings in order to produce myKeys :wink:

myKeys = [
-- some other keybindings
] ++ audioKeys

but you should do whatever works best for your setup. Check out the XMonad config tips for some interesting ideas regarding the structuring of your configuration.