What you need for this book
You will be expected to have knowledge about working with Linux and look to fast-track that knowledge to an expert level. Working along with this book and the exercises therein is recommended and encouraged. Although this book can be used as a "read and learn", I would recommend "read, try, and learn for life". The try bit in the middle is essential to any real understanding and knowledge; this is a pedagogy that has been tried and tested across ages.
At the time of writing this book, CentOS version 6.5 is released, although any version of CentOS is acceptable for most of the exercises, including later versions. Versions of CentOS can be downloaded from http://wiki.centos.org/Download. It is free and open to use, as you will see, under the terms of the GPL license. CentOS 6.5 supports updates free of charge up to November 30, 2020.