Section 3.1. What Tree to Use

3.1. 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 bug fixes 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 3-1. 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 3-1. 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.