I'm running Ubuntu Bionic Beaver inside VirtualBox with Arch Linux 5.3.12 as the host operating system.
I've selected the default options while going through VirtualBox' "Create Virtual Machine" dialog.
I've installed guest additions using
pacman -Sy virtualbox-guest-utils.
This is what I see:
Ubuntu doesn't fill the available space and it doesn't adapt its size when resizing the VirtualBox window.
How can I make Ubuntu inside VirtualBox use all that empty space?