I have a Mac Mini being used as a file server with an external hard drive used to store the shared folders. If the "Ignore ownership on this volume" is not checked, I can control access for specific users using the System Preferences -> Sharing pane.
However, if I check the "Ignore ownership on this volume", all user accounts on the system (including network user accounts created with "Sharing only" option) can read/write to the shared folders over the network. It appears that any sharing & permissions rules are completely ignored on this volume (which I suppose makes sense).
However, why does the system then allow me to add custom access rules to this volume? Do these rules do anything on a volume with "Ignore ownership on this volume" enabled?
Best Answer
When you set a volume to ignore ownership the kernel sets the files on that volume to the user
unknown. Files owned by theunknownuser appear to be owned by any user that can access those files. Still the privileges grant what you can do with any file.