This post assumes that you have Virtualbox 4.1.8 running a fresh copy of Ubuntu 11.10 Server (guest) on Windows 7 (host). After hours of trying to figure out why I couldn’t get Guest Additions installed, I found the answer! I hope this helps…

Update & Upgrade apt-get and get dependancies for Guest Additions.

$ sudo apt-get update && sudo apt-get upgrade

$ sudo apt-get install dkms build-essential linux-headers-generic

Load the Guest Additions ISO from the main terminal window menu. I find it easier to mount this as a cdrom within the guest.

1. Devices > CD/DVD Devices > Choose a virtual CD/DVD disk file…
2. Browse to C:\Program Files\Oracle\VirtualBox and select VBoxGuestAdditions.iso

Mount the VBoxGuestAdditions.iso within Ubuntu.

$ sudo mount /dev/cdrom /media/cdrom

Install the Guest Additions.

$ sudo ./media/cdrom/VBoxLinuxAdditions.run

Reboot.

$ sudo reboot

Mounting Shared Folders. When creating the share folder from the main terminal’s menu, choose Auto-mount and Make Permanent.

With Linux guests, auto-mounted shared folders are mounted into the /media directory, along with the prefix sf_. For example, the shared folder myfiles would be mounted to /media/sf_myfiles on Linux and /mnt/sf_myfiles on Solaris.

NOTE: Access to auto-mounted shared folders is only granted to the user group vboxsf, which is created by the VirtualBox Guest Additions installer. Hence guest users have to be member of that group to have read/write access or to have read-only access in case the folder is not mapped writable.

Add a user to the vboxsf Group to access the mounted shared folders.

$ sudo usermod -G vboxsf -a 'name-of-user'

To assign the new group, log off and reconnect.

All done. At this point, you can access the mounted shared folder. Now, you can use symlinks to make it easier to work with.