Hassio / HassOs is designed to be very small. On a Raspberry Pi you can install Raspian and install hassio on that. You would then have the desktop for your hdmi.
You basically follow the Linux install instructions, except you need to tell the hassio installer your machine type.
I am currently running hassio on Raspian Lite on by RPi.
I don’t need whole raspbian desktop. I just need chrome browser to start/stop some web page on it when I need to show some information from hass on my hdmi display. Because of that I wanna develop hass.io addon on hassos rpi image.
I look in addon developing documentation and I didn’t find right key to open x display on addon start.
You’ll need to look carefully at the structure of hassio addons and develop it.
You perhaps though kinda misunderstand the concept - a network attached device can simply use a web browser on another computer. If you want to deal direct with hassio, use ssh.
I know that, but I think this will be good enhancement for HA.
I seek a way to show HA dashboard or some web page on touch monitor connected directly to hdmi port of hassos host (in my case raspberry pi 3 SCB).
If I accomplished that, then I can automate start/stop of multiple docker container with different stuff to show. (dashboard, clock, photo frame, push notification, media player, …).
There would not be enough demand for the developers to include it in HassOS.
They might be interested in accepting your code submission if you get it working, though
Stop tilting at windmills. HassOS is designed to be an appliance without an attached screen (except the occasional need for a commandline terminal, which is supported).
If you want to attach a screen for GUI purposes, go for another install method.
I already made addon for KODI with GUI. Addon is in early stage but works great.