Making CapsLock Useful... on Solus

I thought I had this figured out…

I previously wrote about fixing the caps lock key in Ubuntu. This more or less worked fine, but it still felt pretty hacky. I wasn’t happy with it, but at the same time I mostly use Windows or macOS as my daily driver, and didn’t spend much time looking for a better solution.

The other day I got fed up (again) with Windows 10, and set up a dual-boot install with Linux. After a bit of searching around, I settled on Solus Budgie as my distro of choice this time. It seems that everyone who uses it vows to never switch to anything else, which isn’t super surprising given the Linux community, but… it looked intriguing. I’ve spent most of my Linux time on Ubuntu or other Debian variants, with a bit of dabbling with Arch when I’m feeling particularly masochistic. Solus isn’t based on either, and it felt like a good time to learn something new so I dove in.

For the most part, it’s been smooth sailing so far, and the majority of the packages I needed were available through eopkg with names similar to what I’d expect from apt-get. When it came time to get caps lock working, though, I found a new solution that looked a bit more stable, in the form of the caps2esc plugin for a tool called interception. Hat tip to Danny Guo’s post that led me to this more reliable alternative to xcape.

caps2esc is a plugin for a tool by the same author called interception, which self-describes as “A minimal composable infrastructure on top of libudev and libevdev”. Anyway, whatever. It looks like it can do what I want, namely to remap caps lock into something useful, and also able to do it without barfing whenever the computer goes to sleep, and without a bunch of hacks and workarounds.

caps2esc has nicely-built packages… for Ubuntu and Arch. Not so much for Solus.

Building from source

Install prerequisites

OK, no problem - just build it myself. This should have been way easier than it was, and I blame myself, mostly. The documentation could’ve been a little more explicit, but I’m also not super familiar with C++ development on Linux, and while I have a general idea of what make does, it’s not something I use regularly. But, in the spirit of not needing to look things up across the internet in the future, here’s what it took for me to get this thing built:

$ sudo eopkg install -c system.devel

This gives you things like cmake & make, gcc & g++, and a bunch of other useful utilities for building other software.

$ sudo eopkg install libevdev-devel libconfig-devel yaml-cpp-devel libboost-devel

This gives you the rest of the libraries needed by both caps2esc and the underlying interception.

Clone the repos and build


$ cd ~/src
$ git clone
$ cd caps2esc
$ cmake -B build -DCMAKE_BUILD_TYPE=Release
$ cmake --build build


$ cd ~/src
$ git clone interception-tools
$ cd interception-tools
$ cmake -B build -DCMAKE_BUILD_TYPE=Release
$ cmake --build build

Copy binaries

You can probably put these wherever you like, as long as it’s on your path. I chose /usr/bin/:

$ sudo cp ~/src/caps2esc/build/caps2esc /usr/bin/
$ cd ~/src/interception-tools/build
$ cp udevmon intercept mux uinput /usr/bin/

Set up a systemd unit file to run intercept

$ cd ~/src/interception-tools
$ sudo cp ./udevmon.service /etc/systemd/system/

If you take a look at the unit file, you’ll see that udevmon will look for a YAML config file at /etc/interception/udevmon.yaml, so let’s create that.

$ sudo mkdir -p /etc/interception
$ sudo vim /etc/interception/udevmon.yaml

Create a config file

The GitLab page has an example config file to use caps2esc correctly with interception:

- JOB: intercept -g $DEVNODE | caps2esc | uinput -d $DEVNODE

Start the service

$ sudo systemctl enable udevmon --now
$ sudo systemctl status udevmon
● udevmon.service - Monitor input devices for launching tasks
     Loaded: loaded (/etc/systemd/system/udevmon.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2021-05-25 17:18:54 PDT; 3h 43min ago
       Docs: man:udev(7)
   Main PID: 30691 (udevmon)
      Tasks: 17 (limit: 77059)
     Memory: 5.5M
        CPU: 10.870s
     CGroup: /system.slice/udevmon.service
             ├─30691 /usr/bin/udevmon -c /etc/interception/udevmon.yaml
             ├─30705 sh -c intercept -g $DEVNODE | caps2esc | uinput -d $DEVNODE
             ├─30706 sh -c intercept -g $DEVNODE | caps2esc | uinput -d $DEVNODE
             ├─30707 sh -c intercept -g $DEVNODE | caps2esc | uinput -d $DEVNODE
             ├─30708 intercept -g /dev/input/event1
             ├─30709 caps2esc
             ├─30710 sh -c intercept -g $DEVNODE | caps2esc | uinput -d $DEVNODE
             ├─30711 uinput -d /dev/input/event1
             ├─30712 intercept -g /dev/input/event2
             ├─30713 caps2esc
             ├─30714 uinput -d /dev/input/event2
             ├─30715 intercept -g /dev/input/event3
             ├─30716 caps2esc
             ├─30717 uinput -d /dev/input/event3
             ├─30718 intercept -g /dev/input/event0
             ├─30719 caps2esc
             └─30720 uinput -d /dev/input/event0

OK, but…

So this is great, and it indeed makes CapsLock behave the way I want it to - Escape when tapped, and Control when held down in combination with another key. All well and good, right?… right?…

Of course it can’t be that simple. Everything worked fine right up until the point where I remapped a few other keys on the keyboard using gnome-tweaks. Although I frequently switch between Windows and macOS, I’m most comfortable with macOS-ish (sort of) modifier keys. I prefer the left-most key on the bottom row to act like a Windows key (i.e., to open up the Start menu or launcher), then the Fn key (which I don’t use), then the Alt/Opt key, then the Command/Control key. gnome-tweaks has this exact swapperoo that I want (called “Left Alt as Ctrl, Left Ctrl as Win, Left Win as Left Alt”, under the “Ctrl position” setting. Great. Enable that, re-login to enable it, and… whoops. Now CapsLock still works as Escape, but no longer works as Ctrl.

A bit of digging around shows that caps2esc doesn’t play well with anything else that modifies the keyboard, particularly if the other mapping has lower priority. Hmm… After trying out a different ways of remapping the keys I wanted, and getting the same results, I finally found another plugin (unofficial) for interception that worked, with a bit of playing around.


This plugin does quite a few different things, but what I really need it for is pretty simple: add another pipeline step in the interception chain that will remap the modifier keys before caps2esc gets hold of them. Instead of having a one-size-fits-all scope, this plugin lets you define your own keymappings in a way that interception can pipeline them.

Here’s what I did:

Clone the repo

$ cd ~/src
$ git clone

Create a new keymapping configuration

$ mkdir ~/src/interception-k2k/default/swapsies
$ nvim ~/src/interception-k2k/default/swapsies/

Add the following to this file:

{ .from_key = KEY_LEFTCTRL, .to_key = KEY_LEFTMETA },
{ .from_key = KEY_LEFTMETA, .to_key = KEY_LEFTALT },
{ .from_key = KEY_LEFTALT, .to_key = KEY_LEFTCTRL }

Build the pipeline step

$ cd ~/src/interception-k2k
$ make
touch default/swapsies/
touch default/swapsies/
cc -std=c99 -O3 -g -Wall -Wextra -Werror -Wno-type-limits -Idefault -Idefault/swapsies k2k.c -o out/swapsies
rm default/swapsies/ default/swapsies/

This builds an executable from the rules I just specified, and puts it in the ./out/ folder.

Move the pipeline executable somewhere sane

$ sudo mkdir -p /opt/interception
$ sudo cp ~/src/interception-k2k/out/swapsies /opt/interception/

Update udevmon to add this pipeline step

IMPORTANT: this step MUST come before the caps2esc step, otherwise it doesn’t fix the problem at all

$ sudo nvim /etc/interception/udevmon.yaml

Add the new pipeline step in the JOB section as the first pipeline. The file should look like this afterwards:

- JOB: intercept -g $DEVNODE | /opt/interception/swapsies | caps2esc | uinput -d $DEVNODE

Restart udevmon

$ sudo systemctl restart udevmon


It took a re-login after this to get things working, after initially finding that my key-repeat and delay settings had been clobbered. After logging out and back in again, though everything seems to be working properly, and I’ve finally got what I wanted.