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keyd++

Linux lacks a good key remapping solution. In order to achieve satisfactory results a medley of tools need to be employed (e.g xcape, xmodmap) with the end result often being tethered to a specified environment (X11). keyd attempts to solve this problem by providing a flexible system wide daemon which remaps keys using kernel level input primitives (evdev, uinput).

keyd++ is a C++ fork of keyd and has specific features at the moment:

  • Rebind any key by its number like key_333. Was not possible in keyd.
  • Macro can now do type(Hello world) without worrying about spaces.
  • Macro can now execute cmd(gnome-terminal) and it should just work.
  • Allow using ctrl as an alias for control (my personal whim).
  • Wildcard for mice m: that excludes problematic abs ptr devices(a:).
  • Layer indicator with keyboard led of choice (keyd has been somewhat broken).
  • More flexible text parsing (in progress, eg. '[a+b]' now equals '[b+a]').
  • Memory optimizations (on small config only 10% of what keyd has had).
  • Performance optimizations, eg. events from ungrabbed device are ignored.
  • Some security improvement: privileged commands only run from /etc/keyd/ conf.
  • Bindings coming from ex. keyd-application-mapper inherit uid+gid+environ.
  • keyd reload from user loads user binds from ~/.config/keyd/bindings.conf.
  • New commands for config control: push, pop, pop_all. Can unload user binds.
  • Convenience and safety coming from C++20. Sorry for longer compilation.
  • Virtually unlimited sizes/counts (keyd has had many hardcoded limitations).

Goals

  • Speed (event loop that takes <<1ms for input event)
  • Simplicity (a config format that is intuitive)
  • Consistency (modifiers that play nicely with layers by default)
  • Modularity (a UNIXy core extensible through the use of an IPC mechanism)

Features

keyd has several unique features many of which are traditionally only found in custom keyboard firmware like QMK as well as some which are unique to keyd.

Some of the more interesting ones include:

  • Layers (with support for hybrid modifiers).
  • Key overloading (different behaviour on tap/hold).
  • Keyboard specific configuration.
  • Instantaneous remapping (no more flashing :)).
  • A client-server model that facilitates scripting and display server agnostic application remapping. (Currently ships with support for X, sway, and gnome (wayland)).
  • System wide config (works in a VT).
  • First class support for modifier overloading.
  • Unicode support.

keyd is for people who:

  • Would like to experiment with custom layers (i.e custom shift keys) and oneshot modifiers.
  • Want to have multiple keyboards with different layouts on the same machine.
  • Want to be able to remap C-1 without breaking modifier semantics.
  • Want a keyboard config format which is easy to grok.
  • Like tiny daemons that adhere to the Unix philosophy.
  • Want to put the control and escape keys where God intended.
  • Wish to be able to switch to a VT to debug something without breaking their keymap.

What keyd isn't:

  • A tool for programming individual key up/down events.

Dependencies

  • C++20 compiler starting from clang++-14 or g++-11
  • Linux kernel headers (already present on most systems)

Optional

  • python (for application specific remapping)
  • python-xlib (only for X support)
  • dbus-python (only for KDE support)

Installation

Note: master serves as the development branch, things may occasionally break.

From Source

# Install dependencies (if necessary)
sudo apt install build-essentials git
# Clone with git clone (.) or download sources manually to keyd directory
cd keyd
# Specify your favourite compiler (optional)
export CXX=clang++-18
# First time install
make && sudo make install && sudo systemctl enable --now keyd
# Second time install (update example)
CXX=clang++-18 make && sudo make install && sudo systemctl daemon-reload && sudo systemctl restart keyd

Quickstart

  1. Install and start keyd (e.g sudo systemctl enable keyd --now)

  2. Put the following in /etc/keyd/default.conf:

[ids]

# Capture all keyboards
k:*

[main]

# Maps capslock to escape when pressed and control when held.
capslock = overload(control, esc)

# Remaps the escape key to capslock
esc = capslock

Key names can be obtained by using the keyd monitor command. Note that while keyd is running, the output of this command will correspond to keyd's output. The original input events can be seen by first stopping keyd and then running the command. See the man page for more details.

  1. Run sudo keyd reload to reload the config set.

  2. See the man page (man keyd) for a more comprehensive description.

Config errors will appear in the log output and can be accessed in the usual way using your system's service manager (e.g sudo journalctl -eu keyd).

Note: It is possible to render your machine unusable with a bad config file. Should you find yourself in this position, the special key sequence backspace+escape+enter should cause keyd to terminate.

Some mice (e.g the Logitech MX Master) are capable of emitting keys and are consequently matched by the wildcard id. It may be necessary to explicitly blacklist these.

User-Level Remapping (experimental)

  • Add yourself to the keyd group:

    usermod -aG keyd <user>

  • Create ~/.config/keyd/bindings.conf:

    E.G. meta.t = macro(cmd(gnome-terminal))

  • Execute keyd reload without sudo (possibly at startup). This is important as mapped commands will run with user privileges.

Application Specific Remapping (experimental)

  • Add yourself to the keyd group:

    usermod -aG keyd <user>

  • Populate ~/.config/keyd/app.conf:

E.G

[alacritty]

alt.] = macro(C-g n)
alt.[ = macro(C-g p)

[chromium]

alt.[ = C-S-tab
alt.] = macro(C-tab)

[org-gnome-nautilus]
# This Meta+F key should open selected file in Nautilus with Firefox.
meta.f = macro(C-c 50ms cmd(xsel -ocb | xargs firefox))

  • Run:

    keyd-application-mapper

You will probably want to put keyd-application-mapper -d somewhere in your display server initialization logic (e.g ~/.xinitrc) unless you are running Gnome.

See the man page for more details.

SBC support

Experimental support for single board computers (SBCs) via usb-gadget has been added courtesy of Giorgi Chavchanidze.

See usb-gadget.md for details.

Packages

Third party packages for the some distributions also exist. If you wish to add yours to the list please file a PR. These are kindly maintained by community members, no personal responsibility is taken for them.

Sample Config

[ids]

k:*

[main]

leftshift = oneshot(shift)
capslock = overload(symbols, esc)

[symbols]

d = ~
f = /
...

Example config

Many users will probably not be interested in taking full advantage of keyd. For those who seek simple quality of life improvements I can recommend the following config:

[ids]

k:*

[main]

shift = oneshot(shift)
meta = oneshot(meta)
control = oneshot(control)

leftalt = oneshot(alt)
rightalt = oneshot(altgr)

capslock = overload(control, esc)
insert = S-insert

This overloads the capslock key to function as both escape (when tapped) and control (when held) and remaps all modifiers to 'oneshot' keys. Thus to produce the letter A you can now simply tap shift and then a instead of having to hold it. Finally it remaps insert to S-insert (paste on X11).