GNOME broken after 16.04 LTS to 18.04 Bionic Beaver upgrade in Virtualbox on Windows 7 host

I have a Windows 7 workstation and I use Virtualbox to run Ubuntu. This is with UI not a headless deal. I try to keep Virtualbox itself and all the Ubuntu packages up to date. I have Virtualbox 5.2.18, currently the latest version available. However my VM image was first created almost 4 years ago and regularly upgraded all this time, even through different Ubuntu dist upgrades.

Today I was offered a release upgrade from 16.04 LTS to 18.04.1 LTS (Bionic Beaver). I saved a snapshot and proceeded with the upgrade. When asked whether to remove obsolete packages, whether I do or not, the result is the same. Afterwards it reboots, and the GNOME desktop environment will not start. It attempts five times, each time with the Virtualbox window assuming the pre-upgrade dimensions, but each time returning to the console without ever showing the login splash screen. The final console message is:

[ OK ] Started GNOME Display Manager.

There is other output on the same line, where it appears a CR without LF was done:

[ OK ] Started GNOME Display Manager.eport generation.......ystem change.pp link was shut down..

I am able to switch to another tty and login using Ctrl+Alt+F2, and I can get root, but I'm not sure what I'm looking for to troubleshoot this. I'm not an expert with GNOME or X. I will provide in edits any info asked for in comments.

To be clear, the VM configuration works just fine before the upgrade to Bionic Beaver. These VM config options seem like they might be relevant:

• OS profile type = "Linux" and version = "Ubuntu (64-bit)"


• chipset = PIIX3


• I/O APIC is enabled


• EFI (special OS only) is disabled


• 2 CPUs in VM (host has 4) with PAE/NX enabled


• paravirtualization interface = "Legacy" (switching to "Default" or "KVM" does not seem to fix the issue by itself, though the 16.04 snapshot works fine with any of these options)


• VT-X is enabled


• nested paging is enabled


• 3d video acceleration is enabled

Is there any path forward with this upgrade that can restore the graphical environment? I would prefer not to start over and install clean, as that would be a major inconvenience and will cost substantial time.

Eventually an 18.04.2 LTS version was offered that did not have this issue. My VirtualBox install is now fully upgraded and working properly.