Lock builtin laptop keyboard but keep an external USB keyboard functioning

I have a laptop but also an external USB keyboard connected to it. Is it somehow possible to lock the built-in laptop keyboard (i.e. keys pressed should have no effect) but keep the external one responsive?

I'm running Ubuntu Gnome 16.04. My laptop is Lenovo ThinkPad T420.

1 Answer

Yes, this should be possible, with the use of xinput.

To start, run xinput list in a terminal. You should see something similar to the following:

zachary@MCServer:~$ xinput list
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)] ↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)] ↳ Power Button id=6 [slave keyboard (3)] ↳ Power Button id=7 [slave keyboard (3)]

Now, you'll probably see two keyboards, instead of just one, since you have two keyboards plugged in. I recommend unplugging the USB keyboard and running the command.

Take note of the ID of Virtual core XTEST keyboard. In my case, it's 5.

Plug in the USB keyboard, since you're about to disable the internal one.

Run this command:

xinput set-prop 5 "Device Enabled" 0

and replace 5 with your device ID.

To re-enable the keyboard:

xinput set-prop 5 "Device Enabled" 1`

replace 5 with your device ID.

You can also put these in separate scripts if you want, and run those from the terminal (or create .desktop files to the scripts you make).

Edit:
If you want, I've made a script that will check the state of the specified device in xinput and toggle it (to on if off, to off if on). You will need to change the device variable to the corresponding ID.

#!/bin/bash
device=5 #Change this to reflect your device's ID
output=$(xinput list-props $device | awk '/Device Enabled/{print $4}')
if [ $output == 1 ] then xinput set-prop $device "Device Enabled" 0
elif [ $output == 0 ] then xinput set-prop $device "Device Enabled" 1
else echo "Something's up."
fi

Edit 2:
Improved script - automatic device ID detection (provided its name is fixed) and desktop notifications.

#!/usr/bin/env bash
# name of the device - we hope this will not change
DEVNAME="AT Translated Set 2 keyboard"
# here we find the device ID corresponding to the name
device=$(xinput list | grep "${DEVNAME}" | sed "s/.*${DEVNAME}.*id=\([0-9]*\).*/\1/g")
# here we get the enabled state
state=$(xinput list-props $device | awk '/Device Enabled/{print $4}')
if [ ${state} == 1 ]; then # if it is enabled, disable it and show a notification xinput set-prop ${device} 'Device Enabled' 0 notify-send -u normal "Keyboard lock" "Keyboard \"${DEVNAME}\" (id=${device}) was disabled."
elif [ ${state} == 0 ]; then # if it is disabled, enable it and show a notification xinput set-prop ${device} 'Device Enabled' 1 notify-send -u normal "Keyboard lock" "Keyboard \"${DEVNAME}\" (id=${device}) was enabled."
else # some weird state - do nothing and show critical notification notify-send -u critical "Keyboard lock" "Keyboard \"${DEVNAME}\" (id=${device}) is neither enabled nor disabled. State is \"${state}\""
fi