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Windows 7: Multi-OS sharing on same computer

02 Oct 2009   #1

Windows XP, Vista, & Ubuntu
Multi-OS sharing on same computer

Hi Guys,

Really hope someone can help me out. The sharing problem I've encountered has really been annoying. Anyway, here's the problem.

I have a Multi-OS unit (Ubuntu, 2x Windows XP Pros, and Windows Vista), the problem started when I installed Windows 7 64bit RC. At first it worked well, then once I started using my media (pictures, music files, videos) whenever I worked on XP and Vista, I couldn't access my files in the media folders. It always says Access denied. I found a small remedy by booting in Windows 7 and then editing the sharing properties, Share with homegroup and adding everybody in the list of people "to share with". The thing is, it doesn't work with some sub folders and files inside sub folders. I end up having to edit each and every shared folder's security/share settings.

The big question I'd like to consult is, if there was some way of resetting the sharing properties of my main/parent folders and reset them and their sub-folder hierarchy.

I understand the problem with security, but I think that it doesn't apply here since its just other OSes within the same system trying to access files inside it.

hope someone can help. thanks in advance

My System SpecsSystem Spec
02 Oct 2009   #2


You're not "sharing" in the network sense implied by this forum's name - the multiple operating systems are simply having trouble dealing with each others file security descriptors on a local drive.

A bit of background...

Each of the Windows OSs you mentioned has its own user database. Those accounts are tracked via a "security identifier" (SID) which is a big ugly string that looks a little like this S-1-5-21-12345678-abcd-4321. That is the real username, in some ways, and it's going to be different for each user in each of your OS installations. As an example, if your two XP installs both have an account called "Bob", the SIDs of those two accounts are going to be entirely different, even though the usernames might be the same.

For NTFS partitions, each file has an Access Control List (ACL) associated with it. The list contains SIDs and their respective access rights: "SIDx - read and write; SIDy - only read".

When it's time to decide whether a user attempting to access a file should be given access, the OS correlates that user's SID to the contents of the file's ACL. If the ACL contains a specific entry for the SID in question or one of the groups that user belongs to, those become the effective access rights. Otherwise, if the SID is simply unmentioned, the effect is an "access denied".

In your case, the problem you've got is that the various OSs have no idea about each other's SIDs because the account databases are entirely separate. There are several workarounds but they're all inelegant. You can continue to edit the ACLs, the way you've been doing, to add more SIDs from different OS installs, or you could enable the "guest" account... or you might even want to consider a FAT32 partition.

I can't recall the last time I actually advised somebody to use FAT32, but in your case it may be useful for what you want to do. Create one or more separate partitions for all the files being commonly shared between the different OSs, and because FAT32 has no concept of security at all (no ACLs), everybody will always have full access to each of those files.
My System SpecsSystem Spec

 Multi-OS sharing on same computer

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