The Linux kernel at work

Until this chapter the kernel was background: it manages the hardware somewhere, and you work with files and processes on top of it. Now we go one level down. The kernel is not a monolith built once and frozen. It loads pieces of code on the fly, holds hundreds of tunable parameters, and exposes two file trees you can talk to it through.

Most of managing the kernel comes down to reading and writing ordinary-looking files. A driver for a new network card, the size of a network buffer, the name of the booted image - all of it is reachable through /proc, /sys, and a couple of utilities on top.

Start with modules. A kernel module is a piece of code the kernel plugs in and unplugs while running, without a reboot. Most often these are device drivers and f