Note: Check out my original article from 2013 about the rationale behind this remapping.

Recently I’ve switched back from macOS to GNU/Linux, as my primary development environment, and I found out that my old article on remapping Enter to Control was no longer the optimal way to achieve this (e.g. - xcape operates at the X level, which means it doesn’t work with Wayland or without a GUI). It took me a bit of digging, but eventually I found dual-function-keys (a plugin for the interception framework), which does exactly what I needed and it does it splendidly.

Unfortunately, the tool is not packaged for most GNU/Linux distros1, but setting it up from source is not that complex. In this article I’ll share instructions that are specific to Ubuntu, but they should be easy to modify for other Linux distros.

Let’s kick it off by downloading and installing the interception framework and dual-function-keys:

# install build deps
$ sudo apt install libudev-dev libyaml-cpp-dev libevdev-dev cmake
# create a folder where to clone the source code
$ mkdir src && cd src
# clone the necessary code
$ git clone https://gitlab.com/interception/linux/tools
$ git clone https://gitlab.com/interception/linux/plugins/dual-function-keys
# build and install the interception framework
$ cd tools
$ mkdir build
$ cd build
$ cmake ..
$ make
$ sudo make install
$ cd ../..
# build the dual-function-keys plugin
$ cd dual-functions-keys
$ make && sudo make install

That wasn’t so hard, right? Now we have to create a couple of configuration files and we’re ready for action. The first one is .dual-function-keys.yaml (normally placed in your home folder):

# /home/username/.dual-function-keys.yaml
TIMING:
  TAP_MILLISEC: 200
  DOUBLE_TAP_MILLISEC: 150

MAPPINGS:
  - KEY: KEY_ENTER
    TAP: KEY_ENTER
    HOLD: KEY_RIGHTCTRL

That’s the main config for dual-function-keys, where we’re specifying the duration of a tap and double tap and our remapping rules. In our case there’s a single rule - Enter acts as Enter on tap (when pressed briefly) and as (right) Control when held down longer.

Then we need to create /etc/udevmon.yaml (you’ll need sudo for this):

# /etc/udevmon.yaml
- JOB: "intercept -g $DEVNODE | dual-function-keys -c /home/bozhidar/.dual-function-keys.yaml | uinput -d $DEVNODE"
  DEVICE:
    EVENTS:
      EV_KEY: [KEY_ENTER]

Note: Update the path the .dual-function-keys.yaml accordingly.

Finally we need to create a systemd service definition file for udevmon and start the new service:

# /etc/systemd/system/udevmon.service

[Unit]
Description=udevmon
Wants=systemd-udev-settle.service
After=systemd-udev-settle.service

[Service]
ExecStart=/usr/bin/nice -n -20 /usr/local/bin/udevmon -c /etc/udevmon.yaml

[Install]
WantedBy=multi-user.target

Now we simply have to enable the udevmon service our remapping will kick in:

$ sudo systemctl enable --now udevmon

That’s all! Now you can start enjoying your beloved productivity boost!

You can achieve a lot more with dual-function-keys, so I’d advice you to explore the tool further. Keep hacking!

Alternatives

Another option I considered was xkeysnail, which seemed a bit simpler to setup, as it’s written in Python, and even has an example config geared towards Emacs users. You might want to check it out.

If someone’s using another approach to achieve the same result I’d love to hear about it!

  1. Seems currently it’s only packaged for Arch Linux and family (e.g. Manjaro). ↩