OS X Mountain Lion Server For Dummies

Standard POSIX Permissions versus ACL Permission Schemes

Mountain Lion Server offers two different kinds of permissions for files and folders. The first, standard POSIX (Portable Operating System Interface for Unix), is from the Unix world. Access control lists (ACLs) are from the Windows world.

Here’s the basic difference between the two: For any share point or shared folder or file, POSIX permissions allow you to set permissions only for the Owner, one Group, and Others. ACLs give you the additional option to set permissions for multiple individuals and multiple groups for a shared item. ACLs also have more types of permissions.

POSIX permissions are easier to use and may be all that a home user needs. ACLs give you a finer degree of control over access to files and folders but can quickly become complicated to manage. ACLs can be useful if you have several departments in an organization that need different levels of access for the same shared folder.

Note, too, that although POSIX permissions can be used with any method of file sharing, ACLs can be used only with the most common file-sharing protocols (which I describe in Chapter 7). Table 8-1 shows the permission types that each file-sharing protocol can use.

Table 8-1 Permission Types Available to File-Sharing Protocols

File-Sharing Protocol	POSIX Permissions	ACL Permissions
AFP (Mac only)	Yes	Yes
SMB (best ...