virtualbox.org

From attached logs, what seems to be the problem with booting the virtual Ubuntu 20 server?

The error seems straightforward: the file claiming to be a VDI is in fact not a VDI. Or the header has been corrupted.

And your report seems to have nothing to do with installing Guest Additions so far as I can see. This is about booting the VM.

A VM log would fill in many of the blanks. Make sure the VM is fully shut down, then right click it in the manager UI. Select "Show Log" and save "VBox.log" (no other file) to a zip file. Attach the zip here.

Attached the logfile and the machine settings. Like you say the problem is with vdi-file.

I add that I did not reboot the server immediately after installation. I just went on with "sudo apt-get update" and mounting GuestAdditions.iso.

I add also that a second identical virtual machine ran into the same vdi-header-problem.

Will report on wether it's my Cloud-drive that messes things up.