Remaping Keys in Ubuntu 17

Question

Please help me solve the following problem: I have a USB pedal that I want to function as Control key for my work. So far system identifies that this pedal is working as F2 key (I am using Ubuntu 17) and I would like to remap the system to understand F2 key as Control key. I have tried several manuals, some of which refer to the Xmodmap solution which seem to be deprecated, another to XKB which I due to my stupidity have failed to understand. I am looking at some suggestions from you as to how can I make this happen. Thanks in advance.

score 0 · Answer 1 · answered Dec 29 '17 at 01:41

XKB method

XKB may not be the best way to change this device's behavior, but it should be possible in traditional X environments. Newer XKB contexts like Wayland or kmscon may not provide the granularity needed to configure separate XKB layouts on arbitrary devices. It also won't function under the traditional console.

Applying a udev hwdb override to make this change should work under all of these.

Under traditional X environments, setxkbmap takes a -device flag and xkbcomp uses -i:

-device device

Specifies the numeric device id of the input device to be updated with the new keyboard layout.

Use xinput -list to find the device id numbers.

To prove this functional, use the setxkbmap ... -print to generate a basic layout, save it to a file, then load that with xkbcomp filename.xkb $DISPLAY. You may need to disable GNOME/KDE's keyboard settings daemons while testing.

$ setxkbmap -layout us -option '' -print > f2toctrl.xkb

Edit the file f2toctrl.xkb -- we're only changing the xkb_symbols line:

// generated with `setxkbmap -print` and modified
// load: xkbcomp -i DeviceID# filename $DISPLAY
xkb_keymap {
    xkb_keycodes  { include "evdev+aliases(qwerty)" };
    xkb_types     { include "complete" };
    xkb_compat    { include "complete" };
    xkb_symbols   {
        include "pc+us+inet(evdev)"

        // existing key definition (see `xkbcomp $DISPLAY - | grep -A 3 FK02`)
        // key <FK02> {
        //    type= "CTRL+ALT",
        //    symbols[Group1]= [ F2, F2, F2, F2, XF86Switch_VT_2 ]
        // };

        // patterned after ctrl:nocaps option
        // see /usr/share/X11/xkb/symbols/ctrl
        replace key <FK02> { [ Control_L, Control_L ] };
        modifier_map  Control { <FK02>, <LCTL> };

    };
    xkb_geometry  { include "pc(pc105)" };
};

Now load it (replace N with the device id you found in xinput -list):

$ xkbcomp -i N f2toctrl.xkb $DISPLAY

You can verify your changes with xkbcomp -i N $DISPLAY - | less, and test the button physically in various applications to make sure it's being recognized.

For normal (non-DE) X environments, the loading command can be added to ~/.xinitrc or other windowmanager startup scripts. You'd need to add that override to the system's XKB database for use with most Wayland compositors and DEs like GNOME/KDE, but in those contexts I'm not certain how you'd apply the override to only the pedal device. If that were feasible, I'd create /usr/share/X11/xkb/symbols/pedal to hold the Ctrl override demonstrated above (and potentially other useful overrides for the device).

A very simplistic layout file might look like this:

// /usr/share/X11/xkb/symbols/pedal

// convert F2 key operation to Ctrl
default partial modifier_keys
xkb_symbols "basic" {
    name[Group1]= "USB Pedal as Ctrl";
    replace key <FK02> { [ Control_L, Control_L ] };
    modifier_map Control { <FK02>, <LCTL> };
};

If you've already applied a hwdb override to make the system see this pedal as F2, changing that to F14 or some other key missing from common keyboards might allow you to merge the XKB solution into your primary layout and let it affect all devices without altering existing keys. that should let it work under XKB contexts that don't enable device-specific keymaps. — quixotic, Dec 29 '17 at 01:43

Remaping Keys in Ubuntu 17

1 Answers1

XKB method