Grampp, F. T., and R. H. Morris. "UNIX Operating System Security," AT&T Bell Laboratories Technical Journal, October 1984. This is the original article on Unix security and remains worth reading.

Wood, Patrick H., and Stephen G. Kochan. UNIX System Security , Carmel, IN: Hayden Books, 1986. A good treatment of Unix System V security prior to the incorporation of TCP/IP networking. Mainly of historical interest.