134 Chapter 6 Table 6.1: Unix Permissions and Chmod chmod Usage User Group Other Read u þ r or 0004 u þ r or 0040 u þ r or 0400 Write u þ w or 0002 u þ w or 0020 u þ w or 0200 Execute u þ x or 0001 u þ x or 0010 u þ x or 0100 Special u þ s or 4000 u þ s or 2000 u þ s or 1000 Processes When a program is executed, it is represented in a Unix system as a process. The kernel keeps track of many pieces of information about each process. This information is required for basic housekeeping and advanced tasks such as tracing and debugging. This information represents the user, group, and other data used for making security decisions about a process's access rights to files and other resources. 2. Hardening Linux and Unix With a basic understanding of the fundamental concepts of the Unix architecture, let's take a look at the practical work of securing a Unix deployment. First we'll review considerations for securing Unix machines from network-borne attacks. Then we'll look at security from