Kernel/Upgrade

This article describes the steps to upgrade to a new kernel.

Installation
A kernel upgrade may be necessary when new kernel sources are installed after a system update or when you yourself install new kernel sources.

Configuration
The configuration parallels that of the manual configuration, since only the config file is reused. All steps are mentioned here again for the sake of completeness, for a more verbose explanation see the other article.

Set symlink
The symlink should always point to the kernel sources that is currently being used. This can be done in one of three ways:


 * 1. Installing the kernel sources with active symlink USE flag
 * This will make the point to your newly installed kernel sources. If necessary, it can still be modified later with the following two methods:


 * 2. Setting the symlink with eselect:




 * This outputs the available kernel sources. The asterisk indicates the chosen sources. To change the kernel sources, e.g. to the second entry, do:




 * 3. Setting the symlink manually:



Sanitize sources
If you are experiencing build problems while rebuilding the current kernel, it might help to sanitize the kernel sources. Make sure you backup the file first, as the operation will remove it. Make sure not to use a  or   suffix as backup as   will clean those up as well.

Copy previous kernel configuration
The configuration from currently running kernel needs to be copied to the new one. It can be found in several places:


 * In the procfs filesystem, if the kernel option Enable access to .config through /proc/config.gz was activated in your present kernel:




 * In the directory, if you installed the config file there:




 * In the kernel directory of the currently-running kernel:



make oldconfig
Now update the previous config file for your new kernel:

The following configuration parallels that of the text based configuration with make config. For every difference between the kernel versions, it asks if you want to activate the driver or feature. An example:

The string (NEW) at the end of the line marks this option as new. Left to the string in square brackets are the possible answers: Yes, no, module or ? to show the help. The recommend answer is capitalized (here Y). The help explains the option or driver.

Unfortunately make oldconfig doesn't show - next to the help - a lot more information for each option, like the context, so that it is sometimes difficult to give the right answer. In this case the best way to go is to remember the option name and revise it afterwards through one of the graphical kernel configuration tools.

Reinstall external kernel modules
Any external kernel modules, such as binary kernel modules, need to be rebuilt for each new kernel. If the kernel hasn't been built yet, it has to first be prepared for the building of the external kernel modules:

You can rebuild the packages using the @module-rebuild set:

Build
For this step, follow the steps in the manual configuration article.

Removing old kernels
See the kernel removal article.

External resources

 * kernel changelog with some explanations of new features