1. Make guest additions iso available on host server
VBoxManage storageattach "
2. Mount cdrom and install/update guest additions in guest
sudo mount /dev/cdrom /media/cdrom
sudo bash /media/cdrom/VBoxLinuxAdditions.run
sudo umount /media/cdom
3. Reboot guest to ensure everything is loaded.
sudo reboot now
4. Remove CD iso
VBoxManage storageattach "