Getting started flashing firmware on Atreus

Hi all! I’ve just received my Atreus and am trying to wrap my head around actually using it. But also I’m trying to build and flash the most recent firmware, and I’m having a problem. I started out by trying to follow the instructions at

This is on Ubuntu 20.04, using Arduino installed via snap. I’ve updated the udev rules to give my user permissions to talk to the device, which udev has linked to /dev/atreus. I’ve rebooted since making those changes.

I’m using the sketch at avr/libraries/Kaleidoscope/examples/Devices/Keyboardio/Atreus from the repo at, which is seemingly what the instructions above were telling me to do.

Ideally I’d like to avoid the Arduino GUI, but make executed from the above directory fails with a complaint that makes it seem that I have some environment variables to track down and set for the project’s expectations. But if I open Atreus.ino using the Arduino GUI, it compiles fine. However, when trying to upload (with the ESC key held down) I get:

avrdude: Version 6.3-20190619
     Copyright (c) 2000-2005 Brian Dean,
     Copyright (c) 2007-2014 Joerg Wunsch

     System wide configuration file is "/home/kor/snap/arduino/41/.arduino15/packages/arduino/tools/avrdude/6.3.0-arduino17/etc/avrdude.conf"
     User configuration file is "/home/kor/snap/arduino/41/.avrduderc"
     User configuration file does not exist or is not a regular file, skipping

     Using Port                    : usb
     Using Programmer              : stk500v2
avrdude: usbdev_open(): did not find any USB device "usb" (0x03eb:0x2104)

avrdude done.  Thank you.

Inside the GUI, the board is identified as Keyboardio Atreus and the port (the only one listed) is /dev/ttyACM0 (Keyboardio Atreus). The programmer selected (I didn’t change this) is AVRISP mkII.

I’d appreciate any hints or pointers towards fixing this!