WARNING: The character device /dev/vboxdrv does not exist.
     Please install the virtualbox-dkms package and the appropriate
     headers, most likely linux-headers-amd64.

     You will not be able to start VMs until this problem is fixed.

# apt-get update; apt-get install virtualbox-dkms linux-headers-amd64

apt-get install linux-headers-$(dpkg --print-architecture) virtualbox-dkms