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When sharing is not enough

October 1, 2009

Vista busy cursor I came perilously close to trashing my entire Vista install, including loss of some files.  Most of my key data is backed up but the consequences would still have been painful, particularly thinking of the time needed to get all my software reinstalled and everything configured.

And it would have been for nothing.  All because I was messing around with folder permissions and not being careful enough.

I was getting cheesed off with not being able to get to some of the folders and files on my Vista desktop’s C: drive from the various household laptops, over the domestic twifi.  I had shared the whole of the C: drive but many key folders, eg the desktop, were not accessible.  I found out that this was because sharing is not enough.  There are two hurdles to be overcome for one PC to access another’s files over a LAN or wifi: the folder must both be shared and have sufficiently relaxed file system permissions. So I set about trying to make everything on the C: drive accessible to Everyone, with Full Control.  It sounds dangerous but isn’t really. The whole network is protected by a fully stealthed NAT router.

Well, it shouldn’t have been dangerous but was nearly terminal, although I didn’t know anything was wrong for a while.  That’s because I have Windows 7 RC installed on another local disk (D:) and decided to boot into that for a while to try a few things out.  Only later did I try to boot back into Vista – and failed.  I got as far as the boot up screen with progress bar then all went black.  The mouse cursor was still visible, and moved in response to the mouse, but that was it.

Not realising the cause of the problem, I proceeded to lose a fair bit of time.  Trying many forms of OS repair from the Vista recovery disk, running Spinrite, pulling my hair out.  I was on the point of giving up and reinstalling Vista from scratch (and losing everything on the C: drive) when I had an idea.  I could boot into Windows 7 from the D: drive then try to recover my files from the C: drive (and save them on my external 1TB drive) before embarking on the Vista reinstall.

So I booted up in Windows 7 and found that the Vista boot drive (which appears as D: from within Windows 7) was greyed out.  If I attempted to explore it I would be fobbed off with an “Access Denied” message.  I found, though, that if I opened an administrator command prompt I could still navigate the disk.  I went so far as to start a massive disk copy from within the DOS prompt, intending to save all the files to the external drive.

Luckily, my brain started to work and it all began to make sense.  The admin command prompt could access the drive because the permissions on it allowed admin access, but there was no access for “regular users” so the drive was greyed out in Windows Explorer.  The penny dropped.  In trying to open up user permissions on that drive I had somehow screwed things up and removed some key access rights so that critical files were no longer accessible at boot time.  So if I could resolve that I might be able to boot up in Vista again.

From within Windows 7 I found I could still access the Properties >Security dialog on the drive and (carefully) give Full Control to Everyone, using UAC to elevate my rights to admin level for the purpose.

And of course that did the trick and I was able to get back into Vista with all data intact.  It had been a very, very near miss and entirely down to my own ineptitude.

From which I learn that if you are going to be an idiot, it helps if the fact of your idiocy can be persuaded to dawn on you in a reasonably timely fashion.

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