VirtualBox shared folders

Here's a little issue I ran across the other day.  I was setting up a VirtualBox VM with an Ubuntu guest and I wanted to add a shared folder.  Simple, right?  Just install the VirtualBox guest additions, configure the shared folder to mount automatically, and it "just works".

The only problem is the permissions.  By default, VirtualBox mounts the shared folder with an owner of root.vboxsf and permissions of "rwxrwx---".  So if you add your user account to the vboxsf group, you get full access.  Everyone else...not so much.  Of course, this isn't inherently a problem.  However, I wanted the Apache process to have read access to this shared folder because I have a web app that needs to read data off of it.  And I didn't really want to give it write access (which it doesn't need), so just adding it to the vboxsf group wasn't a good option.  What I really needed to do was change the permissions with which the share was mounted.

As far as I can tell, there's no way to get VirtualBox to change the permissions.  At least, I didn't see anything in the guest OS and there's no setting in the management UI.  Fortunately, you can pretty easily bypass the auto-mounting.  Since it's a Linux guest, you can just turn off the auto-mounting in the VirtualBox management console and add a line to your /etc/fstab.

There is one issue, though: you have to make sure the vboxsf kernel module is loaded before the system auto-mounts the share.  If you don't the mounting will fail.  However, forcing the module to load is easily accomplished by adding a vboxsf line to your /etc/modules file.

As for the line in /etc/fstab, this seems to work pretty well for me:
SHARE_NAME   /media/somedir   vboxsf   rw,gid=999,dmode=775,fmode=664   0   0

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