Since early 1970, Unix operating system has gone through many metamorphosis. Till today, Unix is believed to be bread and butter of Computer Science internals. This book is an attempt to explain Unix System calls (Internals) in a lucid and problem oriented manner. The examples which are discussed are compiled from the 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. First nine chapters deals 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. Chapter on signals explains the reliable and unreliable way of handling signals while introducing the basic concepts from scratch. Chapters such as pipes, message queues, shared memory, semaphores and memory mapping are dealt in detail with vivid examples. Examples given in processes are very illustrative and concept oriented. Simple examples are taken to explain the concepts in thorough manner."