add_virtualbox_user

link :
http://askubuntu.com/questions/377778/how-to-add-users-to-vboxusers
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sudo usermod -a -G vboxsf your_user_name



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==================install virtualbox 5.1============================
sudo sh -c 'echo "deb http://download.virtualbox.org/virtualbox/debian xenial contrib" >> /etc/apt/sources.list.d/virtualbox.list'


wget -q https://www.virtualbox.org/download/oracle_vbox_2016.asc -O- | sudo apt-key add -


sudo apt update


sudo apt install virtualbox-5.1