The procedure is not best described elsewhere on the web. This article is a mess, too, but it works for me.

Keys need to be remapped to something under keycode 256 in order to work under X11.

• Try using evtest and pressing keys to see what the keys map to right now.
  • evtest can will also tell you what are all the events supported by the device.
  • evtest will show two devices; you are interested in the second one (which exposes all the extended keys, such as new, reply, open, send, etc.
• Use xev to see whether the keys are recognized, and as what are they recognized, in X11.

Now for the juicy part:

# put this into: /etc/udev/hwdb.d/61-keyboard-custom.hwdb

# then to update:
#  sudo udevadm hwdb --update && sudo udevadm control --reload-rules && sudo udevadm control --reload
# and:
#  sudo udevadm trigger
# or:
#  for i in /sys/class/input/* ; do if [[ -e "$i"/id/vendor ]] && [[ -e "$i"/id/product ]] && [[ "$(cat "$i"/id/vendor)" == 045e ]] && [[ "$(cat "$i"/id/product)" == 00db ]] ;  then echo $i ; echo change | sudo tee $i/uevent ; fi ; done

# Natural Keyboard 4000
# formerly:
#keyboard:usb:v045Ep00DB*
# now:
evdev:input:b0003v045Ep00DB*
 KEYBOARD_KEY_0c01ab=finance             # KEY_SPELLCHECK    to KEY_FINANCE
 KEYBOARD_KEY_c022d=up
 KEYBOARD_KEY_c022e=down

We’re naming it 61-keyboard-custom.hwdb in order to have it come after /lib/udev/hwdb.d/60-keyboard.hwdb.

Instead of finance, up and down keys, try taking something from this list: quirk-keymap-list.txt — however, I am not certain how to determine which ones are under 256 except by looking at evtest‘s output.

You can map to keycode 255 and use xmodmap -e "keycode 255 = XF86ZoomIn" to map to a ‘proper’ zoom in key.

On a related note: If you want to remap scancodes to keycodes, you can do it on the fly using setkeycodes(8)

Some sources:

• http://marcin.juszkiewicz.com.pl/2014/03/03/how-to-get-zoom-slider-on-microsoft-keyboard-recognized-by-x11/
• https://unix.stackexchange.com/q/39370

EDIT 2021-01-27:

• Another useful resource is Arch Linux wiki’s article on mapping the scancodes.
• Config files mapping from scancodes to X keycodes can be found in /usr/share/X11/xkb/keycodes. For instance, scancodes generated by evdev are in the file evdev in that directory.
• Scancodes can be found using showkey — which only works from the virtual console, not from within X11.

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via blog.vucica.net