Altering keyboard layout on plugging in or out

Question

I use an external keyboard with my laptop and a script to change the keyboard layout depending on whether the keyboard is plugged in. This works fine, but I find it shouldn't be necessary to run the script manually: it should run by itself whenever the external keyboard is plugged in or out. I've tried to set this up with a udev rule, but for some reason it doesn't work. My udev rule is:

KERNEL=="3-1.1", SUBSYSTEM=="usb", RUN+="/root/bin/udev.sh"

I have confirmed that this script runs once whenever I plug the keyboard in or out. The contents of the script are:

#!/usr/bin/bash
su - toothrot -c "/usr/local/bin/loadkb.sh" &

And the contents of /usr/local/bin/loadkb.sh are:

#!/bin/bash

export DISPLAY=:0 
export XAUTHORITY=/home/toothrot/.Xauthority
export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus

killall xcape

if lsusb | grep HHKB
then {
    setxkbmap us,gr \
        -variant carpalx-plus-intl,daedalus \
        -option grp:win_space_toggle \
        -option lv3:rwin_switch \
        -option altwin:meta_alt \
        -option shift:breaks_caps \
        -option lv5:lsgt_switch_lock
    xmodmap ~/.xmodmap/hh 
    xcape -e 'Shift_L=F13;Shift_R=F14;Super_L=Prior;Hyper_L=Prior'
}
else {
    setxkbmap us,gr \
        -variant carpalx-plus-intl,daedalus \
        -option grp:win_space_toggle \
        -option lv3:ralt_switch \
        -option altwin:meta_alt \
        -option shift:breaks_caps -option lv5:lsgt_switch_lock
    xmodmap ~/.xmodmap/apple
    xcape -e 'Control_L=Escape;Shift_L=F14;Shift_R=F13;Alt_L=Escape;Alt_R=Escape'
}
fi

I have confirmed that running /root/bin/udev.sh as root works for my toothrot X session. Only when run by a udev rule, the script doesn't work. What am I missing?

Or is there a way to achieve the result I want without using a udev rule, maybe from within X?

Answer 1

Inspired by this blog article I got xmodmap to work with the following rule in /etc/udev/rules.d/70-usb-keyboards.rules:

ACTION=="add", ATTRS{idVendor}=="0000", ATTRS{idProduct}=="0000", RUN+="/bin/sh -c 'DISPLAY=:0.0 XAUTHORITY=/home/toothrot/.Xauthority sh -c \"setxkbmap us,gr;xmodmap /home/toothrot/.xmodmap/hh\" &'"

Replace vendor and product id with the values of your device from lsusb and adjust the script to your liking, then don’t forget to reload the udev rules with:

udevadm control --reload

I’d always leave the detection to udev, so this is the rule for when the keyboard is added. To act on removal add another rule line with:

ACTION=="remove"