This book is about Linux from the kernel perspective: we aim to learn about Linux by having a serious peek under the hood of the kernel. This book is intended for an informed Linux enthusiast, one who knows something about Linux (perhaps a great deal in some areas) but is curious about how all the pieces fit together under the control of the kernel. The kernel is highly efficient and designed to be invisible to the untrained eye, and therefore it's easy to miss. This book is intended for those who would like to know how things work "under the hood", but do not necessarily aspire to become kernel developers (so we skip many details, especially details that do not contribute to understanding the principles, for example, device drivers). We examine how the Linux environment operates, how this relates to the design principles of Unix, and why Linux works exactly the way it does. We experiment on the command line (from the Unix shell), by looking into the representative sections of the kernel source code, and by kernel programming (by writing kernel-loadable modules). Specially prepared Kernel Exercises use kernel modules to play with internal kernel structures and illustrate specific points. The exercises involve writing actual kernel modules, inserting them into a running kernel, and observing the effects or outputs. This book is designed so that anyone with a basic knowledge of programming and a working Linux system should be able to follow examples and execute Kernel Exercises. This book is a work in progress (currently ~80% complete). Finally, to those who already bought the book, thank you!