Ubuntu1804 headless box with vino vnc server on, what's difference between Unity mode and gnome mode?

Hello,

Recently I tried to remote login to my headless Jetson Nano through it’s default vino vnc server.

First of all, I fixed a well-known bug inside Ubuntu desktop according this article.
https://blog.hackster.io/getting-started-with-the-nvidia-jetson-nano-developer-kit-43aa7c298797

And then I can config vino vnc server through GUI, as advised in above article too. I select automatically login to current user and then I can remote login Ubuntu desktop to my headless nano box, after completely power cycle. Everything is ok.

But I ran into trouble when I select login to Ubuntu desktop under gnome mode. When I power cycle the headless nano board, this time I can only see a Nvidia logo picture when I remotely connect to vino server. I searched over the forum and internet and get conclusion that this belongs to another known issue.

https://askubuntu.com/questions/1033436/how-to-use-ubuntu-18-04-on-vnc-without-display-attached

So my question is what’s difference between Unity and gnome desktop, to cause this different behavior?
Is there anyway for us to run vino server under gnome mode without installing of this addtional ‘xserver-xorg-video-dummy’?

I can’t add much, but I think the biggest difference is in the login manager itself (the app which asks for password is separate from the logged in desktop, but both usually come as a package pair…the login manager runs as root, and when a user logs in the login manager overwrites itself with the window manager suid as the user). I really can’t remember what it was I saw, but I think there was some new option related to using Vulkan in the greeter/login manager which needed to be disabled for some case (I could be thinking of something else…I could be way off).

The script “startx” basically runs a window manager directly by a particular user and has no login. It is really the login/display manager which runs as a service for automatic GUI setup.

Thanks for comments. Do you know of any reference information for config of greeter/login manager?

I do not. My only configurations have been fixing SElinux issues (and Jetsons don’t use SElinux). I found this to possibly be of interest:
https://vitux.com/some-common-ubuntu-display-managers-and-how-to-switch-between-them/

Each different display manager will work, but the configuration and setup of each will differ.