Mark G. Sobell is President of Sobell Associates Inc., a consulting firm that specializes 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 Red Hat(R) Linux(R), Third Edition"; "A Practical Guide to Linux(R) Commands, Editors, and Shell Programming"; 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.