After installing Virtualbox Guest Addition, we can share folder in our OS into guest Virtualbox. First, we go to shared folder and add new folder to share. Don’t forget to check auto-mount. Start your VM ( which mine is Ubuntu Oneiric 11.10 ) and go to /media to see sf_ubuntu / sf_folder.
When you click on folder, you will get permission denied. Why this happen? It because your user in VM not registered yet in vboxsf group. All you need is add your username into vboxsf group
sudo usermod -G vboxsf -a
Then reboot your VM. Soon as you’re login into VM, you will get full access into shared folder