[SOLVED] unknown filesystem type 'vboxsf'

When i try to share folder between host and guest (ubuntu) in virtual box, i install guest additions, then i open terminal, and type
 sudo mount -t vboxsf share /home/mada/share
But i get error 'uknown filesystem type vboxsf', to solve this, type in the terminal
 sudo chmod 777 /home/mada/ubuntu \
press enter twice, then
 sudo apt-get install virtualbox-ose-guest-utils
After installation complete, type the mount again, and it worked for me.
Note: my shared folder name in host is 'share', same with the guest shared folder name
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