Mount shared folder (vbox) as another user

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http://serverfault.com – I'm trying to mount my vbox shared folder every time my ubuntu starts. So, I added an entry on /etc/init with this: description "mount vboxsf Desktop" start on startup task exec mount -t vboxsf Desktop /var/www/shared Seems to work, except by the fact that all the files are owned by "root", and I don't have permission to write on the folder (neither chmod nor chown seems to be working). So, how can I make all the files under this shared folder to be owned by www-data user/group? Thanks ps.: The main reason for me to have an automatic shared folder, is so I can create/edit files (HowTos)