You’ll need the VirtualBox (1.6 or above) with Guest Additions installed in Ubuntu.
* With the Virtual Machine powered off and selected in VirtualBox, go to:
Machine > Settings > Shared Folders
* For “Folder Path”, click the icon to browse for the folder you want to share.
* For “Folder Name”, enter a name to describe the share. Let's say vshare
* Click “OK” and start the virtual machine again.
* Create a mount point which is basically an empty folder. Example: /vmnt on the Ubuntu guest VM.
* Fire up the terminal and type:
sudo mount -t vboxsf folder_name path_to_mount_pointfolder_name is the name you typed in earlier to describe the share. Example: sudo mount -t vboxsf vshare /vmnt
* You should be able to browse the shared folder now.
VirtualBox Shared Folders on Ubuntu