Mark G. Sobell is President of Sobell Associates Inc., a consulting firm that special izes in UNIX/Linux training, support, and custom software development. He has more than twenty-five years of experience working with UNIX and Linux systems and is the author of many best-selling books, including A Practical Guide to Fedora (TM) and Red Hat (R) Enterprise Linux (R), Fourth Edition; A Practical Guide to Ubuntu Linux (R), Second Edition; and A Practical Guide to UNIX (R)for Mac OS (R) X Users (coauthored with Peter Seebach), all from Prentice Hall; and A Practical Guide to the UNIX System from Addison-Wesley.