Hey folks,
I'm new to the forums, had a problem, found my own solution and decided to share:
I'm running Kali in Virtualbox on a Kubuntu host, and I was having trouble getting guest add-ons to work so I could get a full screen display. I wound up realizing my kernel headers had somehow gone missing, and the headers for my current version were no longer in the repositories. This is why guest add-ons weren't working. I figured I should really update anyways, so I took the easy route and ran a dist-upgrade and rebooted. System came up and I saw emergency mode! I ran journalctl and noticed a dvd drive error.
At this point I remembered I had changed my /etc/fstab sr0 line earlier to run guest add-ons the lazy way, and replaced 'noauto' with 'exec' temporarily. Swapped it back, rebooted, runs like a champ and I now my guest add-ons work correctly and allow full screen.
It was a silly error on my part, but hopefully my mistake helps someone in the future.
