Remapping Caps Lock to Ctrl

February 12, 2017 2-minute read

There are many other ways to do this, but most of the remapping happens at a higher level in the stack. Remapping at udev changes key mappings at the device level, so hopefully it works consistently throughout the whole OS.

Usually, remapping keys using setxkbmap doesn’t work very well with VMware Workstation. On MacOS, remapping Caps Lock to Control works even in the VMs! Pressing Caps Lock while controlling VMs sends a Ctrl keypress to the VM. In Linux, I’ve previously tried remapping using setxkbmap on Linux Mint, and that doesn’t work with VMs.

I’ve tried this on Ubuntu GNOME 16.04.2, and this remapping not only works in X and on the console, but also within VMs (if you press Caps Lock while the VM is in focus, the VM gets Ctrl).

All of this was done on a console (not a terminal in GNOME) because X also captures the keystrokes and works with it another way.

So press ctrl-alt-f1, and login on the console.

You’ve to create a file to update the udev hardware database. I created mine in /lib/udev/hwdb.d/90-keyboard-remap.hwdb. I believe you’ve to pick a number greater than 60, since 60 was used for keyboards.

$ cat /lib/udev/hwdb.d/90-keyboard-remap.hwdb
evdev:input:b0003v258Ap1006*
 KEYBOARD_KEY_70039=leftctrl
$

The first line allows you to match the keyboard you’re using.

The format is described in

$ less /lib/udev/hwdb.d/60-keyboard.hwdb

To find out my keyboard’s vendor and product ID, I used

$ dmesg | grep input

and looked up the correct values. Note that the format requires four hex digits with capitalized alphabets.

To find out the scancode, I used evtest. Some guides tell you to use showkey, but showkey doesn’t seem to be giving the correct scancodes. I suppose showkey only works for PS2 keyboards?

Anyway, I had to install evtest first:

$ sudo apt install evtest

then run evtest

$ evtest

Press the Caps Lock key and see what scancode was captured. Append that number after KEYBOARD_KEY_ in /lib/udev/hwdb.d/90-keyboard-remap.hwdb.

Note: The second line, where you define the mapping, must be prefixed by one and only one space character.

Then, update the hwdb with

$ sudo udevadm hwdb --update

And then reboot

$ sudo reboot