iPhoto: Sharing libraries among multiple users

Important: If two or more users attempt to use the same iPhoto library and the library is not on a volume where permissions are ignored, unexpected results may occur. This includes the inability to see or edit certain photos, or the inability to open the iPhoto library. Follow the steps below to ensure each user has read/write access to the iPhoto Library.

As a precaution, you should make a backup of your iPhoto library before following these steps.

To share your iPhoto library, you will need to move the iPhoto library to a volume where permissions are ignored. There are a couple of ways to do this:

Move the iPhoto library to an external drive

1. Connect an external USB, FireWire, or Thunderbolt drive which has enough free space to contain the library.
2. Select this drive in the Finder.
3. Choose File > Get Info.
4. In the Info window, find the Sharing & Permissions section. You may need to click the disclosure triangle to see the details for this section. 
5. Click the lock in the lower-right corner of the Info window. Enter an administrator name and password when prompted.
6. Select the option to Ignore Permissions on this volume (usually selected by default).
7. Copy your iPhoto library to this drive.

Important: If you have selected this volume for use as a Time Machine backup, you will not be able to select the option to ignore permissions on the same volume. Select a different volume for the destination of your shared iPhoto library.

Keep in mind that while one user is viewing this library from iPhoto, another user will not be able to open this library at the same time. Instead, the following alert message appears indicating that the library is already in use. You will need to quit iPhoto from the other user account before the next user will be able to view or edit this library.

Alternatively, move the iPhoto library to a disk image

1. Open Disk Utility from the /Applications/Utilities/ folder.
2. Choose File > New > Blank Disk Image.
3. Name the disk image.
4. Choose a large enough size from the Size pop-up menu to accommodate your current iPhoto library, plus future expansion.
5. From the Image Format menu choose read/write disk image or sparse disk image (recommended).
6. Save the disk image to a location where other users can access it, such as in /Users/Shared/ on your Macintosh HD.

The disk image should automatically mount when Disk Utility is finished creating it. If it does not, double click the image file in the Finder to mount the image. It should then show up as a mounted volume, just like any other disk.

Drag the iPhoto library to the disk image to make a copy of the whole library. You may want to rename either the original iPhoto Library or the copy on the disk image to make them easier to differentiate.

To point iPhoto towards this library, hold down the Option key on the keyboard when opening iPhoto. iPhoto will prompt you to choose a library. Select the library you copied to the disk image.

iPhoto will now always look for the library on this disk image. You will want to make sure the image is mounted before opening iPhoto if you want to use this library. You can add the disk image to your Login Items to automate mounting the image every time you log in. See Mac OS X: Setting up Login, Startup items for more information.

You will need to change the permissions on the disk image file to allow other users to write to it, and make sure the option to "Ignore ownership on this volume" is enabled on the mounted disk image:

1. Navigate to the disk image; if you saved to the default location, locate the image in /Users/Shared.
2. Select the disk image file.
3. From the File menu, choose Get Info.
4. In the Info window, find the "Sharing & Permissions" section. You may need to click the disclosure triangle to see the details for this section.
5. Click the lock in the bottom-right corner of the Info window. Enter an administrator name and password when prompted.
6. Click the plus button to add other users to the access list. Make sure each specific user has Read & Write access in the Privilege column.
7. Close the Info window.
8. If the disk image is not currently mounted, double-click the image file to mount the image.
9. Select the mounted disk image in the Finder.
10. In the Info window, find the Sharing & Permissions section. You may need to click the disclosure triangle to see the details for this section. 
11. Click the lock in the lower-right corner of the Info window. Enter an administrator name and password when prompted.
12. Select the option to Ignore Permissions on this volume (usually selected by default).

Each user will need to open the disk image before opening iPhoto to access the iPhoto Library.

Note: If a user attempts to open the iPhoto library while in use by another local user, iPhoto will instead display an alert message. This alert will also appear if a local user attempts to use iPhoto from the disk image over a network.