Shared folder permission setting (If you can not access the shared folder)

Problem :

I set up a shared folder in Virtualbox, but I can not access the shared folder.  

Solve :

Installing the VirtualBox Guest Additions  -> Automatically mount shared folders with VirtualBox ("/media /sh_foldername" will be shown) -> Add Ubuntu users to your vboxsf group

$ sudo -s

Input root password

$ usermod -aG vboxsf <youruser>

$ reboot