Earlier today I upgraded my installation of Virtualbox on Windows 10 from 5.0.20 to 5.0.22. This also came up with an update to the guest additions which I installed into my Ubuntu 16.04 guest machine.

After a reboot Ubuntu would no longer boot and instead would flicker as it tried to change the screen resolution inside the virtual machine. This is a known problem in VirtualBox (see: https://www.virtualbox.org/ticket/15526).

I’ve managed to revert VirtualBox and the guest additions back to 5.0.20 using the following steps:

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