How To Share 1 Photos Library Between 2 Users On a Single Mac

I have had no luck with sharing a library in the Shared folder since Catalina.

Even when I give read/write permissions to everyone, for the enclosing folder and the library itself. Whenever I switch between users the library needs repairing, as soon as I launch Photos on the library: It is no problem for a small library, but may be inconvenient for a large library:

I created a second, smaller volume on my system drive, where I am storing the shared libraries, with "Ignore Ownership" enabled. There I can switch freely between users.

A shared folder does not suffice. It will give you access to the library itself, but when you open the library, the file ownership of internal items will change and other users will have to repair the library, before they can open it again.

The only solution with less trouble will be tom put the library on an external volume or a separate partition, where you can set the ignore ownership flag. The ignore ownership flag will allow access to the internal files and folders, even of the ownership is changed, when another user opens the library. It is what Apple recommends here:

Move your Photos library to save space on your Mac - Apple Support

Thomas, which system version is running on your Mac?

The closest thing to a reliable method is to move the Photos library to an external disk with the "Ignore ownership on this volume" option enabled, and to be sure that one user has logged off entirely before the other user logs on that Mac. (You cannot rely on quitting Photos. There are background processes active on your Photos library any time you are logged in.)

I previously saved Photos library at /Users/Shared so other's in the family could also view it (only one at a time).

When the library grew too big, I copied it to an external MacOS Extended (GUID) and now APFS disk with "Ignore ownership on this volume" set (which seems to be the default BTW). I have advised other's in the family to turn on the external disk, then start Photos, then quit Photos and unmount the disk (usually I do all that for them, though). Works OK.

We used Mojave Photos from /Users/Shared and no edits were made (the main archive is in plain folders on external disks). No ownership issues then but maybe we were lucky or later versions are different.

BTW at one point I cloned the library to a Carbon Copy Cloner disk image as a backup and the updates were very fast. But now I no longer do that because the backups are elsewhere anyway.

An APFS extra volume even in the internal disk is a good idea because it reserves space as needed and can use that ignore ownership setting.

I created the screenshot on a Mac with Big Sur. The problem persists in the current version.