Change udev when USB keyboard is present

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1

Hi,

I want to add a piece to my configuration.nix so that the keyboard layout changes when a USB keyboard is present, and I was wondering if there is a NixOS way of accomplishing this. Currently, I have:

services.udev.extraRules = ''
  ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="feed", ATTRS{idProduct}=="0000", RUN+="${pkgs.coreutils}/bin/touch /run/usb-keyboard-connected"
  ACTION=="remove", SUBSYSTEM=="usb", ATTRS{idVendor}=="feed", ATTRS{idProduct}=="0000", RUN+="${pkgs.coreutils}/bin/rm /run/usb-keyboard-connected"
'';

systemd.services.usbKeyboardSwitch = {
  description = "Switch keyboard layout based on external keyboard connection";
  script = ''
    #!/bin/sh
    export DISPLAY=:0
    while true; do
      if [ -e /run/usb-keyboard-connected ]; then
        /run/current-system/sw/bin/runuser -l microbass -c "/run/current-system/sw/bin/setxkbmap us"
      else
        /run/current-system/sw/bin/runuser -l microbass -c "/run/current-system/sw/bin/setxkbmap ie"
      fi
      sleep   10
    done
  '';
  serviceConfig = {
    Type = "simple";
    Environment = "DISPLAY=:0 XAUTHORITY=/home/microbass/.Xauthority";
    User = "microbass";
    Group = "users"; 
    Restart = "always";
    RestartSec = "10";
  };
  wantedBy = [ "multi-user.target" ];
};

but I’m getting permission errors on the above. Is there an option that I’m missing to trigger setxkbmap in userspace?

Thanks, as always!

2

Not sure about the setxkbmap permissions, but you can probably use SYSTEMD_WANTS to avoid the polling, and maybe StopWhenUnneeded to simplify further, something like:

services.udev.extraRules = ''
  SUBSYSTEM=="usb", ATTR{idVendor}=="feed", ATTR{idProduct}=="0000", TAG+="systemd", ENV{SYSTEMD_WANTS}="usb-keyboard.service"
'';

systemd.services.usb-keyboard = {
  unitConfig.StopWhenUnneeded = true;

  script = ''
    echo 'Connected'
  '';

  preStop = ''
    echo 'Disconnected'
  '';
};

The script etc. options don’t need a shebang as they use writeShellScriptBin which already adds one.

And in case you hadn’t seen, there should also be a way to set a different layout for each keyboard though I’m not personally familiar with that.