Comment 10 for bug 1762491

Sorry, I have to take that back (a little): it worked in VMware and in VirtualBox, but I just realized VirtualBox hadn't set the 3d acceleration option when it imported the OVA. So your code (correctly) didn't turn on the OpenGL redirects. If I turn on the 3d acceleration, then it enables /etc/ld.so.conf.d/00vboxvideo.conf, and then graphics are broken in virtualbox (same symptoms as before, lightdm crashes).

This turned out to be because my very stripped-down image was preseeded using
   d-i base-installer/kernel/image string linux-virtual
to avoid getting lots of irrelevant drivers and firmware (stripped a few hundred megs off the OVA). But unlike linux-image-generic, linux-image-virtual doesn't depend on linux-image-extra, which means I didn't have vboxvideo.ko.

Installing virtualbox-guest-dkms fixed this by providing the missing kernel drivers. But that suggests the test for enabling /etc/ld.so.conf.d/00vboxvideo.conf isn't quite thorough enough, though this is probably a bug that should go upstream for VBoxClient --check3d instead of adding more to your script.