CHAPTER 5 Unix and Linux Security Gerald Beuchelt Independent Security Consultant When Unix was first booted on a PDP-8 computer at Bell Labs, it already had a basic notion of user isolation, separation of kernel and user memory space, and pro-cess security. It was originally conceived as a multiuser system, and as such, security could not be added on as an afterthought. In this respect, Unix was different from a whole class of computing machinery that had been targeted at single-user environments. 1. Unix and Security The examples in this chapter refer to the Solaris operating system and Debian-based Linux