Publisher Summary This chapter introduces the concepts of auditing UNIX and Linux. One of the key secrets to auditing UNIX or Linux is to ensure that one must have knowledgeable people available for the audit. The UNIX administrator should know the aspects of system that is configured. This provides a wealth of information that was not necessarily readily available. Various UNIX checklists when coupled from sources such as the Centre for Internet Security (CIS) and NIST, the development of a comprehensive UNIX audit program becomes simple. The primary point to remember is that UNIX was designed for programmers. The default UNIX shells are in effect miniature program interpreters and the system is a development environment with a simple and open default security model. UNIX shells are in themselves powerful scripting engines with programming capabilities that range from the ability to implement simple filters and searches and create program batches through to the ability to run complex programs such as Web servers.