The first edition, originally published in 1994 by John Wiley, was named an Alternate Main Selection of the Newbridge Book Club. It stayed in print for thirteen years, an eternity in the computing literature. Due to changes in the publishing industry, this edition of the book is only available electronically. I revised the book because of the increased popularity of several variants of UNIX and what I learned from reviews of the previous published version. Linux is highly popular, especially in the open source community and because the operating system for the Google Android phone is based on it. Mach, Solaris, and Apple Darwin are also popular. In my experience, end users, application programmers, system programmers, and system administrators often have difficulties making programs and utilities work well across different UNIX variants, due to differences in file system organization, different locations of critical configuration files, and important, yet subtle, differences in how system calls operate. There are also issues with different utilities, many of which are either not available on all UNIX versions, or else require a substantial effort to even get them to install properly. One of the most interesting problems required detailed analysis of several Linux variants in order to get a single public domain application to work: the different Linux variants from Fedora (formerly Red Hat), SUSE, and Ubuntu were tried before the application would install and work properly. 

Many second editions dump material from older technologies. I have chosen a different approach, guided by my own research and experience in the efficient development of large, high-quality, software systems over much of the last twenty-five years. A huge percentage of current software applications for UNIX and other operating systems are built using existing software components that are either partially or entirely reused. Older software components necessarily have been built using older technology and are likely to use some of the classic system calls.