Install VirtualBox Guest Additions in
Add this to /etc/apt/sources.list:
deb http://http.us.debian.org/debian sid main non-free contrib
Update repositories and install package
sudo apt-get update
sudo apt-get install virtualbox-guest-dkms
deb http://http.us.debian.org/debian sid main non-free contrib
Update repositories and install package
sudo apt-get update
sudo apt-get install virtualbox-guest-dkms