Synopsis This book is an attempt to explain Unix system calls (internals) in a lucid and problem oriented manner. The examples which are discussed are the result of author’s lectures at RITCH center and also from the suggestions (answers) made by thousands of Unix enthusiasts in USENET groups on Unix, and personnel web pages of many Linux enthusiasts. This book assumes that the prosperous reader has no hands on exposure to Unix Operating System. However, it assumes that he has good exposure to theoretical aspects of Operating Systems Design and 'C' programming. First nine chapters deal with "how to get hands on exposure to Unix Operating System". Subsequent chapters explain "Unix internal programming". All the examples given are tested under Linux environment.