Comment 43 for bug 1386005

I don't know if this is considered recovery mode but going this route allowed me to workaround it (am running Ubuntu MATE 15.04 Beta 2 in a Virtualbox guest), but of course no longer have a graphical boot..:
http://ubuntuforums.org/showthread.php?t=2251116&p=13158092#post13158092

Martin Wimpress lists what I did as a solution to Virtualbox Guests showing up as 640x480 resolution.
https://ubuntu-mate.org/blog/ubuntu-mate-vivid-beta2/#disqus_thread