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Appendix
B
B ACL Permissions and Group
Memberships Using GUID
Mac OS X Server version 10.4 introduces a new user and
group attribute for determining file system permissions
and group membership.
Mac OS X version 10.4 departs from the historical UNIX practices of:
• Basing file system permissions only on the UID and GID attributes
• Basing group membership on the user short name
This departure allows Mac OS X version 10.4 to augment standard POSIX file system
permissions with access control lists (ACLs). It also allows Mac OS X version 10.4 to
maintain group memberships when user short names are changed and to support
nested group membership.
This improvement in functionality does not remove or change POSIX permissions, nor
does it affect interoperability of Mac OS X with legacy UNIX systems or other operating
systems.
Important: After upgrading or migrating your server to Mac OS X Server version 10.4, it
is highly advisable to create a new backup by exporting existing user and group
accounts, which now have GUID attributes. If you need to restore user or group
accounts in the future, this new export file will enable you to import the users and
groups with their GUIDs intact.
Understanding GUIDs
Beginning with Mac OS X version 10.4, a universal ID called a globally unique identifier
(GUID, pronounced GOO-id) provides user and group identity for ACL permissions. The
GUID also associates a user with group and nested group memberships.
The administration tools in Mac OS X Server version 10.2 and later automatically assign
a new GUID to every new user account and to every user account that’s imported, but
Mac OS X version 10.4 is the first version to use GUIDs and to include GUIDs in export
files. The GUID is a hidden attribute. To view the GUID attribute, use Inspector in
Workgroup Manager.
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