Remap keys on Ubuntu keyboard.

 I finally found the right way to remap keys in Ubuntu. 

This only works for later versions of udev so check your version.

> udevadm --version

Should be 240+

> sudo systemd-hwdb update   # if it's not

First find the keyboard to remap

> sudo evtest

pick the keyboard by event id. Note the id (say it's 4)

press keys you want to remap and note the 'value' on the MSC_SCAN line on the key you want to change

press the key you want to map to and note the KEY_XXXX code

We will need the modalias, so 
> cat /sys/class/input/event4/device/modalias

Now you need to make a file
> sudo gedit  /etc/udev/hwdb.d/10-my-modifiers.hwdb 

Here is mine:

evdev:input:b0011v0001p0001*
 KEYBOARD_KEY_db=leftalt
 KEYBOARD_KEY_38=leftmeta

The format needs to be exact. There is one space before KEYBOARD_XXX.

The key codes are lowercase.

So now you need to load the config
> sudo udevadm trigger

> udevadm info /dev/input/event4 | grep KEYBOARD

You should see your mappings are active.

Now even if you reboot your mappings should still be there.