I'm running VirtualBox 4.1.14, host is iMac OS X 10.7.3, guest is Ubuntu 12.04. I want to share folders between the two, ideally access to external hard-drives that are my storage for the Mac. Have put the hard drives in the lists in 'Shared Folders' in set-up in VB, but struggling with various suggestions using a Terminal in the VM. The extension pack is installed, I'm pretty new to Ubuntu, so still a novice with the apps etc, but it isn't totally strange! Is Samba of any use to me? Doesn't appear to be... but willing to take advice. Have successfully shared drives between Mac host and Windows 7 guest, so guessing it's a Ubuntu issue... offers?
You probably don't have the correct group permissions in your Ubuntu guest to mount the shared folders. Run the following in your guest OS:
sudo addgroup --system vboxsf sudo adduser $LOGNAME vboxsf
You will need to reboot or login again for the group permissions to take effect. If you've set up the folders correctly for auto-mounting, they will be mounted under /media after your next reboot. If not, once your groups are correct, you can mount the folders manually with:
sudo mount -t vboxsf -o uid=$UID,gid=$(id -g) [sharename] [mountpoint]
See the Guest Additions: Shared Folders section of the manual for more information.