Install dkms package:
In VirtualBox: menu Devices -> Insert Guest Additions CD Image.
Back in linux:
sudo apt-get install dkms
In VirtualBox: menu Devices -> Insert Guest Additions CD Image.
Back in linux:
sudo apt-get update && sudo apt-get install build-essential dkms linux-headers-$(uname -r)
cd /mnt
sudo ./VBoxLinuxAdditions.run
sudo reboot