Copy/paste text from Ubuntu 18.10 (Cosmic Cuttlefish) VM from/to Windows host using VirtualBox

Tested on:
Host: Windows 10 Enterprise (1803) with VirtualBox 5.2.20
Guest: Ubuntu 18.10 (Cosmic Cuttlefish)

Goal: Copy/paste text from/to Ubuntu 18.10 from/to Windows host

Solution:

This is not absolutely necessary but it is a good practice to update Ubuntu 18.10 to the latest using a terminal, like:

$ sudo apt update
$ sudo apt upgrade
$ sudo apt autoremove

I would advice to reboot the machine at this point so that we will be running the latest kernel. The next command may also pick the wrong version of the kernel headers if the machine(VM) is running the older version of the kernel. Now, install dkms so that VirtualBox guest additions can be compiled as part of the kernel, like:

$ sudo apt install dkms

Now mount VirtualBox guest additions, this will be done from the external/host UI of the VirtualBox guest VM. For example, click on Devices | Insert Guest Additions CD Image... Now head into the VM and do:

$ cd /media/<username>/VBox_GAs_5.2.20
$ sudo ./VBoxLinuxAdditions.run

Of course you have to change VBox_GAs_5.2.20 to the version of VirtualBox version you are using. 

Then reboot the machine. To copy/paste do Devices | Shared Clipboard | Bidirectional or other options as appropriate. Copy/paste between the host and VM should now work.