kbct: A Rust repository from andreyk0

KBCT - Keyboard Customization Tool for Linux ⚙️ 💻 🐧

KBCT is yet another tool that will help to remap keys across the desktop environment.

When is KBCT useful?

If you want to have a custom ergonomic keyboard layout (when your fingers almost never need to leave the home row keys).
If you're an ex MacOS user and want something similar to Karabiner Elements.
If you want to achieve something similar to QMK layers on your laptop keyboard.
If you want to have system-wide vim-like navigation mapping some_modifier + hjkl to arrow keys.
If you find xbindkeys ,xmodmap and setxkbmap ~~impossible~~ hard to configure.
If you want your mapping configuration to work on both Wayland and X11.
If you want to remap buttons on your mouse or other input devices.
If you want the configuration to be simple and intuitive.

*However, KBCT is not a tool that can be used to configure macros or arbitrary command execution on a key press. Also note that KBCT requires sudo access.

**KBCT is in active development so expect to see some bugs, however it should be stable enough for simple use cases. In any case create an issue if you encounter something unexpected.

Installation

There are several ways of installing KBCT

Download the pre-built x86_64 AppImage binary from releases.

cd ~/Downloads
wget https://github.com/samvel1024/kbct/releases/latest/download/kbct-x86_64.AppImage
chmod +x kbct-x86_64.AppImage

#Check that it works
sudo ./kbct-x86_64.AppImage list-devices

Compile from the sources by first installing libudev1 and libudev-dev packages (available for all known distributions).

sudo apt install libudev1 && \
  sudo apt install libudev-dev  # for ubuntu/debian

Then assuming that you have a Rust toolchain installed run the following.

cd /tmp &&
git clone https://github.com/samvel1024/kbct && \
cd kbct && \
cargo build --release && \
./target/release/kbct --help

Install from the AUR

If you are an Arch Linux user, you can install it from AUR:
```
$ yay -S kbct-git
```
Note: The configuration file is expected to be in /etc/kbct/config.yml.

After the installation, run the systemd service (remember to modprobe uinput first):
```
$ systemctl start kbct
```

Configuration

KBCT uses YAML files as configuration. It allows to apply different mapping rules for different keyboards. There are two main types of key mappings

keymap: maps keys 1-1 regardless of any layer modifiers. (e.g capslock -> leftctrl)
layers: maps keys based on the active layer. Layer is a key map that will activate and override the existing mapping if a given set of keys are pressed. Much like fn key is combined with F1-F12 keys. (e.g rightalt+i=up or rightalt+leftctrl+comma=volumeup )

The following is an exhaustive example configuration of KBCT

# Apply this configuration to two keyboards (if connected)
- keyboards: [ "Lenovo TrackPoint Keyboard II", "AT Translated Set 2 keyboard"]

  keymap:
    leftalt: leftctrl
    capslock: leftalt
    sysrq: rightmeta
  # Specify layered configurations (much similar to fn+F keys)
  layers:
    # Specify the modifiers of the layer
    - modifiers: ['rightalt']
      keymap:
        i: up
        j: left
        k: down
        l: right
        u: pageup
        o: pagedown
        p: home
        semicolon: end

As a result the above configuration will have the following effect

# ↓/↑ stand for press/release events
# One to one example
leftalt↓ ⟶ leftctrl↓
leftalt↑ ⟶ leftctrl↑

# Layer example
rightalt↓ ⟶ rightalt↓
i↓ ⟶ rightalt↑ up↓
i↑ ⟶ up↑
rightalt↑ ⟶ ∅

Load uinput module (kbct will not function but will not produce an error if the uinput module is not loaded)

sudo modprobe uinput

To start KBCT based on YAML configuration file run:

sudo kbct remap --config ~/.config/kbct.yaml

Here you can find all the available key names to use in the configuration. Essentially those are taken from Linux API headers. In case you want to disable a key map it to reserved. For example disabling capslock will look like this capslock: reserved.

Hint: To begin with, you might want to start KBCT in debugging mode, until you arrive at a working configuration.

Important note: KBCT is treating leftshift/rightshift , leftalt/rightalt, etc. as different keys, so if you want to map both you need to define the mapping twice. This is done on purpose to give fine grained control over configuration.

Troubleshooting

What is the name of my keyboard? In order to list all the available keyboard devices and their respective names run the following:

sudo kbct list-devices

Most often a keyboard laptop will be named AT Translated Set 2 keyboard. If you're not sure what the name of your keyboard is, run sudo evtest, select a device from a list and try typing. If it lets you type without spitting output, you selected a wrong device. Repeat until you see output like this:

Event: time 1641154916.130391, -------------- SYN_REPORT ------------
Event: time 1641154916.130391, type 4 (EV_MSC), code 4 (MSC_SCAN), value 7004f
Event: time 1641154916.130391, type 1 (EV_KEY), code 106 (KEY_RIGHT), value 0
Event: time 1641154916.130391, -------------- SYN_REPORT ------------

What are the names of the keys? KBCT uses the lowest possible level keycodes from the Linux kernel to perform remapping. Window managers/desktop environments may have other namings for the same keys for various reasons. To know the exact name of the key you're interested you can use either sudo evtest /dev/input/event<i>, or sudo kbct log-keys --device-path /dev/input/event<i> where <i> should be replaced by the appropriate device number. You can then start typing to see the key names.

Debugging KBCT In order to start KBCT in debug mode, you may run the following line:

sudo RUST_BACKTRACE=1 kbct --debug-log remap --config <CONFIG-PATH>

When you now press key combinations, you will see the following pattern: DEBUG kbct > +KEY_NAME -> +KEY_NAME. The left hand side of -> corresponds to the input that KBCT receives, whereas the right hand side represents what KBCT proxies the current key state to.

The + refers to a keydown-event and the - refers to a keyup-event.

HINT: If KBCT behaves erroneously after a config change, it may be worth a try to reload the uinput kernel module using sudo modprobe uinput before restarting KBCT.

How it works

KBCT is operating on a low enough level to be independent from the window manager or the desktop environment. It is achieved by the following steps:

Since KBCT should be run as root, it has enough privileges to read and grab the output of a keyboard or another input device (e.g the output of /dev/input/event2). Which means that it becomes readable only for KBCT and that the display manager is no longer able to read from that device.

Then KBCT creates another virtual uinputdevice (e.g. /dev/input/event6), and sends customized key events to that device. The new mapped keyboard or device is successfully read by the window manager, which as a result reads customized key events.

Examples