Installing Virutal Box Guest Additions on Debian

I had a little nightmare with this and couldn't get my head round why I didnt have the kernel headers even though I had installed build-essential. So here's how I did it.

sudo apt-get update -y
sudo apt-get upgrade -y
sudo apt-get install build-essential module-assistant -y
sudo m-a prepare -y

Click on Install Guest Additions from the Devices menu:

Then cancel the autorun prompt as that never works!

Finally,
sudo sh /media/cdrom/VBoxLinuxAdditions.run, and follow the instructions on screen

Restart your VM and it should be job done.

HTH!