Q:

Offline Files; Warn When Another User Has The Same File Open

We are using Windows Server 2008 R2 and have enabled offline files.  We need offline files for the synchronization features and to allow them to take laptops out into the field.  
However whilst our users are in the office and online we would prefer windows to show a warning if a user attempts to open the same file another user has open.
Is this possible?

A:

Unlikely. Microsoft Office apps achieve this by using lock files, but that's obviously done at the application level and has nothing to do with the filesystem itself.
If you need to be able to ensure that file edits are not inadvertently overwritten by others with the same file open, you'll probably have to look at some kind of revision control system. Sharepoint, perhaps?

