PowerTunes > Help > Details on sharing and permissions

Details on sharing and permissions

In order to allow multiple users to use an iTunes library or media folder, PowerTunes changes the permissions of the shared files/folders using a feature introduced in OS X 10.4 (Tiger), ACLs (for a quick overview of how ACLs work, refer to this page on Apple's website). There are two main reasons PowerTunes uses ACLs over the more traditional POSIX permissions model.


First, ACLs provide much finer control over permissions and allow PowerTunes to share with specific users, whereas this is not possible with POSIX permissions. For example, if you have a computer set up for your family, you can choose to have a library shared that only be accessed from mom and dad's accounts, but not the kids.


Second, ACLs provide an inheritance feature that will cause any new files created inside a folder to be assigned the same permissions as the folder itself. This is necessary when sharing a media folder, since if one user imports new files into iTunes and they are put in the shared media folder, those files will automatically be given the necessary permissions for other users to be able to read and write those files without having to reapply permissions for the new files manually.


If you share a library or media folder with a set of specific users, PowerTunes will assign an ACL to each file and folder containing one ACL entry for each user, giving that user read and write permission to the file/folder. When sharing with all users, PowerTunes insteads uses an ACL with a single entry, giving the "everyone" group read/write access to the file/folder. These permissions will be applied recursively to the entire media folder for a shared media folder, but are only applied to the library file and its associated files when sharing a library. Note that PowerTunes will overwrite any existing ACLs that are on those files/folders, although th POSIX permissions on those files will remain the same. If you change a previously shared library to be shared with nobody, PowerTunes will remove all ACLs on the shared files/folders.

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