I have tried this:
sudo apt-get install virtualbox-guest-dkms and enabling bidirectional shared clipboard.
and various other things, now hard to collect, but nothing works so far.
How to fix it?
When trying to insert guest additions CD image, I get this error:
From this question, Unable to Install Guest Additions CD Image on Virtual Box, I tried:
sudo apt-get upgrade sudo apt-get install virtualbox-guest-additions-iso and this gives:
Restarting the virtual machine did not help, no errors.