In general, having multiple user accounts for each family member on a single Mac makes sense. Especially, since user switching is very comfortable nowadays. Since all open programs and data is saved when the user is switched, everyone can have their own workspace.
But even though you have separate accounts, you might want to share a common Photos (or iPhoto) library. This makes sense if you have lots of pictures and don’t want to duplicate them onto multiple accounts.
One recent solution for this is iCloud. By uploading all your pictures to the iCloud you can easily mirror them back to your other devices (also iOS devices) and share them with your family.
But if you don’t want to upload your photos into the cloud or just want to share them among several user accounts on a local Mac, then the following could be interesting for:
How to share one Photos library among several local users
1.) Create a new library in your /Users/Shared/ directory on your Mac.
To do this, open the Photos app on your Mac and immediately hold down the Option key afterwards. A new pop-up window will open up asking you to choose your Photos library or to create a new one. Click on “Create new…” and create a new library. Best place for this library would be the /Users/Shared folder since it is accessible by all users on your Mac.
2.) Adjust the permissions of the library so all users can access it.
This step is a bit tricky since it involves using the terminal. Adjusting the user rights with the Finder does not work since it will only change the standard unix permissions but not the ACLs (access control list) of the photos library. ACLs are an extension to the classic unix permissions and are used by OSX to control permissions. At this point it’s worth noting that the photos library is nothing else but a folder with a bunch of sub-directories. All the sub-directories are just hidden in the Finder but can be accessed i.e. through the terminal.
a.) Open up the terminal. (i.e. go to Spotlight and type terminal).
b.) Navigate to the folder and view the ACL permissions of the newly created photos library folder.
You will see an ACL permission for your user name (the one user that has created the library).
c.) To clear everything up, delete the old ACL permissions with
sudo chmod -N <library_name>
You need to have admin rights to do this, which is why you are prompted for your admin password at this step. <library_name> is replaced with the name of the library file you’ve created.
d.) Now, add the new ACLs recursively to the library file
sudo chmod -R +a “username allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,file_inherit,directory_inherit” library_name
Replace username with the user that you want to give access to and library_name again with the name of the library file you’ve created. If you copy and paste the above string into a terminal, then also replace as well the ” with the one from your keyboard in the terminal window.
The command will give all the rights to that user in order to edit, create and delete files within the library folder or any of its subdirectories. New photos added to the library will automatically get the correct ACLs since ACLs are passed on from the “parent” to the “child”. Therefore, this is a one time step that doesn’t need to be repeated again.
e.) Repeat the previous step for all the users on your Mac. If you now type again “ls -e” you will see something like the following:
0: user:username1 allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity
1: user:username2 allow list,add_file,search,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity
f.) Make this library the default library for all user accounts. This is done by logging in with that particular user and again start the Photos app and holding down the Option key afterwards. Now select the new library.
That’s it . Now all users will be able to access this library and add photos to it. There’s just one limitation to it, that is as long as someone has the library opened, other users won’t be able to open it at the same time. Meaning, once you are finished adding, editing viewing photos just close the Photos app and the next user can open it again.