I have a raspberry pi 3 with a minimal version of Debian stretch installed. The serial output works fine, however, I can't get any output via HDMI. There is actually HDMI output (monitor is having a signal) but the screen is blank. I also get output if I install some xorg packages and run startx. So I think it is somehow related to the tty not being active so more like a general linux/systemd issue and not related to HDMI. So what packages or configuration do I need to get a login prompt or output over HDMI on consoles other than serial?