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Propagate POSIX Permissions in Lion Server

When you configure file sharing in Lion Server, you generally set permissions for one or more shared folders (share points). Usually, users can create new files or folders and can copy files into a folder. Rather than having to set Owner and Group permissions for every new file and folder, these child folders and files are automatically assigned permissions based on rules.

All the file-sharing protocols can use the standard POSIX permissions behavior. The AFP and SMB protocols have another option for propagating POSIX permissions, dubbed Inherit Permissions from Parent or just Inherit Permissions. With this method, new files and folders inherit certain permissions from the parent folder (the folder in which the files and folders are created).

Standard POSIX permissions behavior

In the standard behavior, permissions are assigned for new files and folders on a share point, regardless of what the permissions are on the parent folder. New files or folders get these permissions:

  • Owner: The user who created the new folder or file becomes the owner and is assigned read/write permissions.

  • Group: The new file or folder inherits the group assigned to the parent folder; however, the group is assigned read-only permissions.

  • Everyone/Other: Is assigned read-only permissions.

Files and folders copied to the share point or duplicated don’t inherit any permissions from the parent folder:

  • Owner: The user who created the folder or file remains the owner and is assigned read/write permissions. This is just as with new files and folders.

  • Group: Retains the group and permissions of the original file or folder.

  • Everyone/Other: Retains permissions of the original file or folder.

These are only the default rules. Administrators can change the permissions of new or copied files and folders.

Inherit permissions from parent

In addition to standard POSIX permissions behavior, the AFP and SMB protocols support a model for propagating POSIX permissions that can be more convenient. It’s an inheritance model, in which certain permissions are inherited from the parent folder. Here’s how it works:

  • Folders: New folders, folders that are copied into the share point (parent folder), and duplicated folders inherit the Owner, Group, and Everyone permissions from the parent folder.

  • Files: New files, files that are copied into the share point, or duplicated files. For these, the Owner inheritance is different from that for Groups and Everyone:

    • Owner: The owner/user who created the file or copied it to the shared folder remains the owner.

    • Group and Other/Everyone: The Group and Other/Everyone permissions are inherited from the parent folder. In other words, if a user copies a file or folder into a share point that uses the inheritance model, the Group permissions change. This is different from standard POSIX permissions behavior.

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