VirtualBox shared folder write permission - Ubuntu 12.04

I'm using the following command to mount my folder in VirtualBox:

sudo \mount -t vboxsf -o rw -o uid=1000 -o gid=1000 Dropbox ~/Dropbox/

However, the folder is read-only. I re-installed Guest additions, and made sure the folder is not set as read-only in VirtualBox.

What's the right command to gain write permissions?

Solution 1:

The right command is:

sudo mount -t vboxsf -o rw,uid=1000,gid=1000,dmode=755,fmode=644 Dropbox ~/Dropbox/

Notice the fmode.