Learning Modern Linux

Chapter 2. The Linux Kernel

In “Why an Operating System at All?”, we learned that the main function of an operating system is to abstract over different hardware and provide us with an API. Programming against this API allows us to write applications without having to worry about where and how they are executed. In a nutshell, the kernel provides such an API to programs.

In this chapter, we discuss what the Linux kernel is and how you should be thinking about it as a whole as well as about its components. You will learn about the overall Linux architecture and the essential role the Linux kernel plays. One main takeaway of this chapter is that while the kernel provides all the core functionality, on its own it is not the operating system but only a very central part of it.

First, we take a bird’s-eye view, looking at how the kernel fits in and interacts with the underlying hardware. Then, we review the computational core, discussing different CPU architectures and how they relate to the kernel. Next, we zoom in on the individual kernel components and discuss the API the kernel provides to programs you can run. Finally, we look at how to customize and extend the Linux kernel.

The purpose of this chapter is to equip you with the necessary terminology, make you aware of the interfacing between programs and the kernel, and give you a basic idea what the functionality is. The chapter does not aim to turn you into a kernel developer or even a sysadmin configuring and compiling kernels. ...