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KERNEL UPGRADING

Inevitably it happens: you have a custom-built kernel, working just wonderfully except for one little thing that you know is fixed in the latest release from the kernel developers. Or a security problem is found, and a new stable kernel release is made public. Either way, you are faced with the issue of upgrading the kernel and you do not want to lose all the time and effort that went into making that perfect kernel configuration.
This chapter is going to show how easy it is to update a kernel from an older versions, while still retaining all of the configuration options from the previous one.
First off, please back up the .config file in the kernel source directory. You have spent some time and effort into creating it, and it should be saved in case something goes wrong when trying to upgrade.
$ cd ~/linux/linux-2.6.17.11
$ cp .config ../good_config
Only five simple steps are needed to upgrade a kernel from a previously built one:
1. Get the new source code.?
2. Apply the changes to the old source tree to bring it up to the newer level.
3. Reconfigure the kernel based on the previous kernel configuration.
4. Build the new kernel.
5. Install the new kernel.
The last two steps work the same as described before, so we will only discuss the first three steps in this chapter.
In this chapter, we are going to assume that you have built a successful 2.6.17.9 kernel release, and want to upgrade to the 2.6.17.11 release.

Download the New Source

The Linux kernel developers realize that users do not wish to download the entire source code to the kernel for every update. That would be a waste of bandwidth and time. Because of this, they offer a patch that can upgrade an older kernel release to a newer one.*
On the main kernel.org web site, you will remember that it contained a list ofthe current kernel versions that are available for download, as shown in figure
Image:Kernel.jpg
Previously, you used the link pointed to you by the F to download the entire source code for the kernel.
However, if you click on the name of the kernel release, it will download a patch file instead, as shown in Figure 6-2.