debian on vbox
https://wiki.debian.org/VirtualBox
guest Addition
sudo apt install build-essential dkms linux-headers-$(uname -r)
cd /media/cdrom
sudo chmod +x ./VBoxLinuxAdditions.run
sudo ./VBoxLinuxAdditions.run
sudo usermod -aG vboxsf $(whoami)
sudo reboot
sudo mount /dev/cdrom /media/cdrom