The host system is an iMAC:
macOS Mojave Version 10.14.5 iMac (Retina 5K, 27-inch, Late 2015) Processor 4 GHz Intel Core i7 Memory 16 GB 1867 MHz DDR3 Graphics AMD Radeon R9 M395X 4 GB
Version: 6.08 r130520 (Qt5.6.3) VirtualBox 6.0.8 Oracle VM VirtualBox Extension Pack
The virtual machine is Ubuntu 14.04. In the virtual machine I have installed the guest additions:
sudo apt-get install virtualbox-guest-dkms
I restarted the VM after installing this. The problem is that in the System Settings / Screen Display I still only see a resolution of 640 x 480 (4:3) with no option to select a higher resolution.
What haven't I done?