40fe0930_Reviewing_Where_We_Stand__EROS
[0] 4. [UNIX] Persistent Objects are ACL-based, ephemeral objects are capability based. Strictly speaking, neither statement is true. The user/group/other notion isn't strictly an ACL model, and there are namespaces in UNIX, notably sockets and processes, that are not referenced by descriptors. All of these may be viewed as historical artifacts that could readily be repaired without changing the basic UNIX model (as was largely done in Plan 9). [EROS] 
Everything is a Capability. All object references are performed via capabilities. There is no notion of ``principal,'' which makes auditing relatively difficult to do correctly.
Reviewing Where We Stand
EROS