In other words, does it just hide the permissions on file, or change them? More specifically, if you have a volume with file on it that have different owners and you check Ignore ownership on this volume, and then later you uncheck it, will the original ownerships/permissions revive correctly?
I have not seen anything that answers this directly, although what I have seen about problems with Ignore ownership settings needing to be reset and about them being recorded in
/var/db/volinfo.database suggest that the answer to my questions is yes. Nevertheless, it would be very reassuring if someone could confirm this.
(The context is that I have a bootable backup on an external disk that I would like to keep the permissions intact on so that I can boot from it if needed, but I would also like to be able to read from it on another computer where the users don’t match up to give me access to the relevant files. Being able to switch Ignore ownership on for the latter, and then switch it off again to leave the disk in good condition for potential boot/restore use, looks like it would be a nice, simple way of doing this, but I am concerned about breaking things if I experiment.)