The owner of an information resource can grant other users read or write access rights for that resource. A user who is granted access rights to a resource can transfer those rights to other users.
Users have user-based access only to the objects they own.
Typically, users receive either the group permissions or the default permissions for a resource. The major task in administering access control is to define the group memberships of users, because these memberships determine the users' access rights to the files they do not own. With extended permissions , you can permit or deny file access to specific individuals or groups without changing the base permissions. Access control lists are maintained by the aclget , acledit , and the aclput commands. If you use the numeric mode of the chmod command on a file that has an ACL, extended permissions are disabled.