This book is an outgrowth of the popularity of Linux. Its original version, UNIX for Programmers and Users, written by Graham and updated in subsequent editions by King has been widely used in classroom settings and is popular with professionals new to UNIX or UNIX programming. The increasing popularity of Linux created a demand for a Linux version of such a book, especially in classrooms where Linux is emerging as the platform of choice for computer science students. Graham wrote the original version in response to the need for course material for university students as well as professional programmers, taking great care to include many different types of users in his target audience. He created a book that was helpful to everyone from a complete beginner to an experienced programmer and allowed instructors to teach a variety of courses. The widespread use of Linux has led to the same need for Linux users and instructors.

When my editors at Prentice-Hall first approached me about creating a Linux version of the book, my flippant response was "Fine, change 'UNIX' to 'Linux' on the cover and ship it!" That response was made in jest, of course, but I also thought it was rooted in some amount of truth. I had used many versions of both UNIX and Linux in the past several years, and they seemed all the same to me (which is a strength of both Linux and UNIX). But this similarity is only skin deep. Experienced UNIX users will feel very comfortable with Linux because it adheres to a specified standard for portable operating systems, which means that it provides a specific set of commands, applications, library functions, and system calls. Most of the commands and system calls behave similarly to, if not exactly the same as, those in most versions of UNIX. Some Linux commands have been renamed for various reasons, but in most cases the old UNIX name is usually available as an equivalent.

While, on the surface, Linux looks just like UNIX (which is the whole idea behind having a standard), the implementation is another story. With the benefit of thousands of volunteer programers unencumbered by marketing departments and product release schedules (i.e., "business issues") but armed with years of advances in operating-systems understanding, Linux is actually a significant improvement of an already good idea. When you look "under the hood," you will find that Linux is a much cleaner implementation because it doesn't suffer from the long evolution and tangled code base that plagues many versions of UNIX today. And so this Linux-specific book is actually very different from its UNIX counterpart. Even where the substance is similar to UNIX, the details and examples may vary greatly. Substantive differences include a new chapter on installing Linux and largely revised chapters on the internal workings of Linux and system administration. While we could not possibly cover every detail of every command or application that comes with Linux (without creating a multivolume set!), we try to cover the basics and the most often used utilities to provide a solid foundation upon which you can continue to build your understanding of Linux and the GNU utilities.