Over on the MPCNC forum, Jeffeb3 has made a Rasbian image for Raspberry Pi that already contains Octopi and Cncjs. The link below will point you to everything you need. It also has a link to a “How To” by Daniel Dunn that has a simple step-by-step to loading only Cncjs…but Jeffeb3’s image is super simple.
I am using Jeffeb3’s image to run both my 3d printer(Octopi) AND my MPCNC(Cncjs) at the same time from one Pi Zero W. I am running my Shapeoko on a separate Pi Zero W that only has Cncjs.
I’m sharing this because the instructions (that I could find) that otherwise exist to load Cncjs are not easy to follow, especially if you aren’t familiar with the unix command line.