Updated: September 12, 2025
Recently, I encountered a weird little problem. An inconsistent little problem, too. On a Linux host, I have two Linux virtual machines configured in VirtualBox, both Kubuntu 24.04. One uses LUKS encryption, set up as part of the operating system installation, the other does not. Both use Guest Additions, installed from the official repositories. The former throws an error.
It reads: vmugfx 0000:00:02 .0: [drm] *ERROR* vmugfx seems to be running on an unsupported hypervisor. This configuration is likely broken. Please switch to a supported graphics device to avoid problems. Now, this error only shows during the boot sequence. And it does not seem to affect the functionality of the virtual machine in any way. Screen resizing, screen lock, none of it. But still, let's get rid of it, shall we.
The clue is in the error description
As it happens, while the error message is extremely nerdy, it actually makes sense. VirtualBox tells us to switch to a supported graphics device. And then, I remembered writing about the black screen issues with Linux guests some time ago. Perhaps I need to change the graphics controller used by the affected Kubuntu instance?
Indeed, this solves the problem. I switched from VMSVGA to VboxVGA. The end result is quite good:
- No more vmugfx errors at the boot stage.
- Previously, the VM resolution would change wildly during the boot sequence, often multiple times, going from something like 1280x1024 to whatever I had set the machine to use, and back, and then again to the desired size and resolution. With VboxVGA, it stays put, and the display does not resize. It always matches the VirtualBox window frame, however big it may be.
- The virtual machine works as before, without any kinks. Neither the screen timeout on the host or the guest affects the behavior. No black screen, no lockup. Perfectly smooth execution.
Conclusion
This is a very short tutorial, I must say, but then, they don't always have to be too long. The most important lesson is not to go wild with reinstalling Guest Additions (from the repo or the ISO), fiddling with the display settings insides the virtual machine or similar. After all, if it works for one, it ought to work for both. The question is, of course, why the difference? My guess is it has to do with the decryption prompt shown early in the process.
With the vmugfx error, there would be no nice "box" to input the password, only a pure text-only prompt shown at a separate screen. With the VboxVGA controller, and the error gone, you get the nice elegant password field, the splash animation, all of it. So I guess there's something in the Ubuntu/Kubuntu boot process that may throw off the default graphics controller. And you likely won't fix that by any changes inside the virtual machine. But a simple, quick, nondestructive change of the controller does the job. Take care.
Cheers.