That book is really something special. The author tries to provide an overview of what DevSecOps is. He correctly states, that this term - alongside others - is kind of a not well defined buzzword.
The actual content of the book tries to walk a silver line, starting with basics of TCP/IP and various protocols, over bash scripting, over docker and kubernetes. However, everything is so vague that literally blogposts with a read time of 15 minutes include more practical and useful examples. The book is full of rants, e.g. against systemd, but the actual value of the tools described is near zero. To showcase, the book explains how to install docker, pull docker images and list running docker containers. That's it. Same level of complexity on Bash scripting or k8s.
I can really not recommend this book. As it has been part of HumbleBundle I got it, but even that price was too much, imho.