Is it possible to create keymappings with modifiers CTRL, fn, Super etc?

[einarpersson]

Hi!

I have followed the user configuration guide.

I have managed to create a custom layout which I use for remapping some keys, including combinations with Shift, Alt, AltGr. But is it possible at all to do key remappings / layout changes so that something that Ctrl-j is mapped to down and Ctrl-k is mapped to up? And how about other keys such as Fn, Super/Windows, ? Or do I have to resort to some other program for that kind of capability? (it would be nice if I could do it all with xkb which is builtin).

(Using Fedora 42 KDE Plasma)

Grateful for any advice!

EDIT: If someone could just provide a snippet (if possible) of how to map Ctrl-j to pressing the down arrow that would be great.

[wismill]

But is it possible at all to do key remappings / layout changes so that something that Ctrl-j is mapped to down and Ctrl-k is mapped to up?

Yes, you can map any keysym to any modifier combination, including Down and Up.

But you are going to face the issue #145: not all applications will ignore the consumed modifiers. So when pressing Ctrl-j, apps will get Down + Control modifier is active. Then is it up to each app to use the API correctly to see that Control is consumed and ignore it, so get actually only Down. Some respect that, lots do not (it may have changed, it’s difficult to follow).

So the answer is probably no with only libxkbcommon in its current state, because unless you check each app, you may face unexpected behavior difficult to debug.

For now I would advise to use a third-party software such as KMonad, Kanata or keyd.

But keep informed by subscribing to #145, I intend to tackle this soon™.

And how about other keys such as Fn

Unless you have a specific keyboard, most keyboard do not send events for Fn, so it is impossible to remap with software: you will have to modify the firmware in some way: enable built-in options or reprogram the firmware, if possible.

[einarpersson]

Thank you for thorough answer!