I have built several embedded linux distributions for raspberry pi using buildroot. I have had great luck with it. There is a bit of a learning curve, but that seems to be the case with most embedded devices. I would recommend anyone getting started to try it out.
My favorite is using Nerves system that uses buildroot and boots directly to Elixir. Buildroot can be a bit of a pain but it’s fun to get a 20 mb Linux image with a few commands.
