Unix is an operating system that began development almost 40 years ago. It has a very simple mechanism for controlling access to protected resources based on the owner-group-world model. This simple model has not attracted much interest from the access control community. In this paper we argue that the Unix access control mechanism has some interesting features of relevance to modern authorization services. We present a formal model for the Unix access control mechanism and compare its characteristics with those of role-based access control and XACML, two popular foundations for authorization services. We then discuss what lessons may be learned from the Unix model and how those lessons might be applied in the future.