So far this has happened twice, and it doesn't happen every time I toggle full screen mode. The solution that worked for me was to remove the system level and user level mesa shader cache folders $ sudo rm -rf /var/lib/gdm3/.cache/mesa_shader_cacheĪfter both were removed, the graphical user login screen was displayed on start up and after logging in, the full Gnome desktop created by the original installation was displayed. My Ubuntu 18 VM crashed for the second time, when I was returning to the VM's full screen mode. Which led me (via this post) to the mesa_shader_cache. I (eventually) found the significant failure in the journalctl -b log wsone-VirtualBox kernel: traps: gnome-shell trap invalid opcode ip:7f44240a60d3 sp:7ffe59ab40a0 error:0 I was then able to use + to switch to a tty login. In the end there is only a blinking text cursor in the top level corner. After the OS boots with the graphical loading screen the screen turns black, occasionally showing the mouse cursor as multiple attempts to start the Gnome greeter login screen fail. I'd imported a VirtualBox 6.1.28 OVA for a VM with Ubuntu 20.04.3 Gnome desktop set up for one user. In my case the blank, black screen was not caused by VirtualBox settings, it was the GDM mesa shader cache created by the original Ubuntu installation.

Ubuntu virtualbox full screen