Ubuntu 18.04 (and 19.03) has an older version of the VirtualBox Guest Additions preinstalled. The "normal" method of using the VirtualBox Guest Additions image (VBoxGuestAdditions.iso) to upgrade doesn't work unless the preinstalled Guest Additions are removed first.
-
Run the following commands:
sudo apt remove virtualbox-guest-utils sudo apt purge virtualbox-guest-utils
-
Reboot the VM
Before installing the current Guest Additions, run the following command to install the packages needed to build kernel modules:
sudo apt install gcc make perlThe .iso image can then be used to install the current version of the Guest Additions.