It's quite easy to install Virtual Box Additions under Windows.

You just mount the .iso file and double click on the drive under

My Computer. It gets installed and once you set up shared

directory in VirtualBox for the choosen virtual a new drive

appears under My Computer. Boom done.

But under Linux it's not that easy. Sometimes you don't even

have a graphical environment installed (yet) and you just want

to access your host filesystem. I couldn't find any official

guide but I figured that out. Here is what made the trick for

me.

To prepare the virtual

select the virtual you want to modify on the left side. right click -> Settings. click Shared Folders and then the tiny directory icon

with green plus to add a new shared directory set following: Folder Path: "/"

Folder Name: ROOT (should get filled in automatically)

Make Permanent: check hit OK button. start the virtual.

To prepare the machine

switch to root user with su command. run mkdir /media/root . run apt update . run apt install linux-headers-$(uname -r) gcc make bzip2 .

To install the additions

in the running Virtual window hit Devices on the top then

Insert Guest Additions CD Image run mount /media/cdrom run cd /media/cdrom run sh VBoxLinuxAdditions.run run mount -t vboxsf ROOT /media/root