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-edge, 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 2 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. stable branch (Linux kernel) source code, kernelretrievingwhich tree to use source code, kernelretrieving -rc versions, kernel getting kernel downloading kernel development branch (Linux kernel) 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.

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. wget utility web sitesmain kernel.org site versions, kernelcurrent, for different kernel trees stable kernel version, downloading latest source code, kernelretrievingwhere to find kernel source kernel.org web sitesmain site kernel.org web sites command linedownloading kernel source All of the source code for the Linux kernel can be found on one of the kernel.org sites, a worldwide network of servers that mirror the Linux source code, enabling anyone to find a local server close to him. This allows the main kernel servers to be responsive to the mirror sites, and lets users download the needed files as quickly as possible. The main http://www.kernel.org site shows all of the current kernel versions for the various different kernel trees, as shown in Figure 3-2.

To download the latest stable kernel version, click on the F character on the line for the kernel version. This will download the full source tree. Or you can navigate to the proper subdirectory for all of the 2.6 kernel versions, http://www.us.kernel.org/pub/linux/kernel/v2.6/, shown in Figure 3-3.

It is also possible to download the kernel source from the command line, using the wget or curl utilities, both of which should come with your Linux distribution. To download the 2.6.17.8 kernel version using wget, enter: $ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.17.8.tar.gz --17:44:55-- http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.17.8.tar.gz => `linux-2.6.17.8.tar.gz' Resolving www.kernel.org... 204.152.191.5, 204.152.191.37 Connecting to www.kernel.org|204.152.191.5|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 51,707,742 (49M) [application/x-gzip] 100%[=============================================>] 51,707,742 35.25K/s ETA 00:00 18:02:48 (47.12 KB/s) - `linux-2.6.17.8.tar.gz' saved [51707742/51707742] To download it using curl: $ curl http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.17.8.tar.gz \ -o linux-2.6.17.8.tar.gz % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 49.3M 100 49.3M 0 0 50298 0 0:17:08 0:17:08 --:--:-- 100k For a quick and easy way to determine the latest kernel versions, use the information available at http://www.kernel.org/kdist/finger_banner, illustrated by Figure 3-4.

versions, kerneldetermining latest uncompressing files source code, kernelretrievingwhat to do with the source linux/ directory for kernel source files latest kernel versions, determining curl utility, downloading kernel source Now that you have downloaded the proper kernel source, where is it supposed to go? We suggest creating a local directory in your home directory called linux to hold all of the different kernel source files: $ mkdir ˜/linux Now move the source code into this directory: $ mv ˜/linux-2.6.17.8.tar.gz ˜/linux/ And go into the linux directory: $ cd ˜/linux $ ls linux-2.6.17.8.tar.gz Now that the source code is in the proper directory, uncompress the tree: $ tar -xzvf linux-2.6.17.8.tar.gz The screen will be filled with files that are uncompressed, and you will be left with the following in the linux/ directory: $ ls linux-2.6.17.8.tar.gz linux-2.6.17.8/