I have a few PC Engines APU units that do not have a graphics adapter, and are designed to be setup via a serial interface.
The first step is to find the mini.iso that is made available on the mirrors. This ~75MB image is the core installer for Ubuntu and it will download the items needed to complete your install as it runs, instead of it being pre-loaded onto a larger ISO image. Ubuntu does not make it that easy to find anymore, but if you know where to look you can find what you need.
Head to the below link, and then navigate into the version of Ubuntu you’re looking to install.… Click here to read more!