For various reasons, I moved my Users directory to its own partition following Mike Bombich's excellent instructions.

Some time later, I was adding a new user to my system when I discovered that everything in the Users directory was owned by myself (the admin) and by group "unknown". Even the home directories of all other users were owned by the admin, and trying to change them with the chown command had no effect. The reason for this was that the "Ignore ownership on this volume" checkbox in the Get Info" pane was enabled on the drive that contained my Users directory.

However, I had come to this conclusion while at work, away from my machine, so I was looking for a way to restore ownerships remotely via the terminal. I found the answer on the Apple Developer site, on a page discussing disk permissions.

The command you need to use is vsdbutil. Unfortunately, it doesn't have a man page, but the syntax is fairly simple. To ignore ownerships on a volume, do:

 % sudo vsdbutil -d /VolumeName

To restore ownerships on a volume, do:

 % sudo vsdbutil -a /VolumeName

And to check the status of ownerships on a volume, do:

 % sudo vsdbutil -c /VolumeName

You must have admin privileges to execute the vsdbutil command.