If you keep one Linux book next to your machine then this has *got* to be it.
This is not a tutorial book and it is most useful to those with at least an initial familiarity with Linux. 'Instant Reference' means just that, and on that score, this book delivers big time !
The book is not written in an archaic alphabetical order but a much more useful, logical order grouping related commands together - tremendously practical. The 'At a Glance' section at the beginning of each chapter tells you exactly how to perform the most common tasks. After that, after some tips and explanations of the area of Linux the chapter covers,it launches into a plain English explanation of each command under that topic *and* what all the extensions do, as well as associated system files that are affected.
If you are ever sitting at your Linux terminal and wondering how do I do 'x' (which covers most Linux users, most days) then this book is a must have because you simply reach over open it up and it tells you. I have had some pretty good Linux books but if I had to keep one, the decision would be easy.