In the spring semester of 1997, we taught a course on operating systems based on Linux 2.0. The idea was to encourage students to read the source code. To achieve this, we assigned term projects consisting of making changes to the kernel and performing tests on the modified version. We also wrote course notes for our students about a few critical features of Linux such as task switching and task scheduling.
Out of this work — and with a lot of support from our O'Reilly editor Andy Oram — came the first edition of Understanding the Linux Kernel and the end of 2000, which covered Linux 2.2 with a few anticipations on Linux 2.4. The success encountered by this book encouraged us to continue along this line, and in the fall of 2001 we started planning a second edition covering Linux 2.4. However, Linux 2.4 is quite different from Linux 2.2. Just to mention a few examples, the virtual memory system is entirely new, support for multiprocessor systems is much better, and whole new classes of hardware devices have been added. As a result, we had to rewrite from scratch two-thirds of the book, increasing its size by roughly 25 percent.
As in our first experience, we read thousands of lines of code, trying to make sense of them. After all this work, we can say that it was worth the effort. We learned a lot of things you don't find in books, and we hope we have succeeded in conveying some of this information in the following pages.
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