evremap

A keyboard input remapper for Linux/Wayland systems, written by @wez

Why?

I couldn't find a good solution for the following:

• Remap the CAPSLOCK key so that it produces CTRL when held, but ESC if tapped
• Remap N keys to M keys. Eg: F3 -> CTRL+c, and ALT+LEFT to HOME

How?

evremap works by grabbing exclusive access to an input device and maintaining a model of the keys that are pressed. It then applies your remapping configuration to produce the effective set of pressed keys and emits appropriate changes to a virtual output device.

Because evremap targets the evdev layer of libinput, its remapping is effective system-wide: in Wayland, X11 and the linux console.

Configuration

Here's an example configuration that makes capslock useful:

# The name of the device to remap.
# Run `sudo evremap list-devices` to see the devices available
# on your system.
device_name = "AT Translated Set 2 keyboard"

# If you have multiple devices with the same name, you can optionally
# specify the `phys` value that is printed by the `list-devices` subcommand
# phys = "usb-0000:07:00.3-2.1.1/input0"

# Configure CAPSLOCK as a Dual Role key.
# Holding it produces LEFTCTRL, but tapping it
# will produce ESC.
# Both `tap` and `hold` can expand to multiple output keys.
[[dual_role]]
input = "KEY_CAPSLOCK"
hold = ["KEY_LEFTCTRL"]
tap = ["KEY_ESC"]

You can also express simple remapping entries:

# This config snippet is useful if your keyboard has an arrow
# cluster, but doesn't have page up, page down, home or end
# keys.  Here we're configuring ALT+arrow to map to those functions.
[[remap]]
input = ["KEY_LEFTALT", "KEY_UP"]
output = ["KEY_PAGEUP"]

[[remap]]
input = ["KEY_LEFTALT", "KEY_DOWN"]
output = ["KEY_PAGEDOWN"]

[[remap]]
input = ["KEY_LEFTALT", "KEY_LEFT"]
output = ["KEY_HOME"]

[[remap]]
input = ["KEY_LEFTALT", "KEY_RIGHT"]
output = ["KEY_END"]

When applying remapping configuration, ordering is important:

• Dual Role entries are always processed first
• Remap entries are applied in the order that they appear in your configuration file

Here's an example where ordering is important: on the PixelBook Go keyboard, the function key row has alternate functions on the keycaps. It is natural to want the mute button to mute by default, but to emit the F8 key when holding alt. We can express that with the following configuration:

[[remap]]
input = ["KEY_LEFTALT", "KEY_F8"]
# When our `input` is matched, our list of `output` is prevented from
# matching as the `input` of subsequent rules.
output = ["KEY_F8"]

[[remap]]
input = ["KEY_F8"]
output = ["KEY_MUTE"]

• How do I list available input devices? sudo evremap list-devices

• How do I list available key codes? evremap list-keys

Building it

$ sudo dnf install libevdev-devel
$ cargo build --release

Running it

To run the remapper, invoke it as root (so that it can grab exclusive access to the input device):

$ sudo target/release/evremap remap my-config-file.toml

Or, grant an unprivileged user access to evdev and uinput. On Ubuntu, this can be configured by running the following commands and rebooting:

sudo gpasswd -a YOUR_USER input
echo 'KERNEL=="uinput", GROUP="input"' | sudo tee /etc/udev/rules.d/input.rules

For some platforms, you might need to create an input group first and run:

echo 'KERNEL=="event*", NAME="input/%k", MODE="660", GROUP="input"' | sudo tee /etc/udev/rules.d/input.rules

as well.

Systemd

A sample system service unit is included in the repo. You'll want to adjust the paths to match your system and then install and enable it:

$ sudo cp evremap.service /usr/lib/systemd/system/
$ sudo systemctl daemon-reload
$ sudo systemctl enable evremap.service
$ sudo systemctl start evremap.service

How do I make this execute a command when a key is pressed?

That feature is not implemented.