[ubuntu] can't use shared folder in VirtualBox with Ubuntu Server

I installed a new instance of Ubuntu Server 14.04 in VirtualBox, but I can't get the shared folder functionality to work. I can't see the shared folder even though it's supposed to be automounted. The Guest Additions may not have installed correctly: I checked using "modprobe vboxadd" and "modprobe vboxvfs", but these returned "modprobe: FATAL: Module vboxadd not found" and "modprobe: FATAL: Module vboxvfs not found".

I followed this instruction:
- Start the Ubuntu Server VM and insert the Guest Additions CD image (Devices menu, Install Guest Additions).
- $ sudo mount /dev/cdrom /media/cdrom
- $ sudo apt-get install -y dkms build-essential linux-headers-generic linux-headers-$(uname -r)
- $ sudo /media/cdrom/VBoxLinuxAdditions.run
(from http://en.ig.ma/notebook/2012/virtua...-ubuntu-server )

I also tried:
sudo apt-get install virtualbox-guest-utils
as well as:
sudo apt-get install --no-install-recommends virtualbox-guest-utils && sudo apt-get install virtualbox-guest-dkms

But none of these worked for me.

One page suggested to load the vboxvfs kernel module. I put vboxvfs as well as vboxsf in /etc/modules, but that didn't work.

Any other ideas would be appreciated, thanks.