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Chapter 4.  Retrieving the kernel source

When you're building your own kernel, you want the latest stable release. Many distributions provide their own packages of kernel sources, but these are rarely the most cutting-enge, recent versions. The distribution packages have the advantage of being built to be compatible with the compiler and other tools provided by the distribution (Chapter 3, Requirements for building and using the kernel explains the importance of their being compatible) but they may not end up providing the functionality or performance you want. If you can create your own environment with the latest kernel, compiler, and other tools, you will be able to build exactly what you want. This chapter focuses on determining which kernel sources to download, and how to obtain them.

What tree to use

In the past, the Linux kernel was split into only two trees, the "development" branch and the "stable" branch. The development branch was denoted by an odd number for the second release number, while the stable branch used even numbers. So, as an example, the 2.5.25 release was a development kernel, while the 2.4.25 release is a stable release.

But after the 2.6 series was created, the kernel developers decided to abandon this method of having two separate trees, and declared that all 2.6 kernel releases would be considered "stable", no matter how quickly development was happening. The few months between the major 2.6 releases would allow kernel developers the time to add new features and then stabilize them in time for the next release. Combined with this, a "-stable" kernel branch has been created that releases bugfixes and security updates for the past kernel release, before the next major 2.6 release happens.

This is all best explained with some examples, illustrated in Figure 4.1, “Kernel development release cycle”. The kernel team released the 2.6.17 kernel as a stable release. Then the developers started working on new features and started releasing the -rc versions as development kernels so that people could help test and debug the changes. After everyone agreed that the development release was stable enough, it was released as the 2.6.18 kernel. This whole cycle usually takes about two to three months, depending on a variety of factors.

Figure 4.1. Kernel development release cycle

Kernel development release cycle

While the development of the new features was happening, the 2.6.17.1, 2.6.17.2, and other stable kernel versions were released, containing bug fixes and security updates.

If you wish to just use the latest kernel for your work, it is recommended that you use the stable kernel releases. If you wish to help the kernel developers test the features of the next kernel release and give them feedback, use the development kernel release. For the purpose of this chapter, we will assume that you are using a stable kernel release.


 
 
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