The kernel is the core of the operating system. Containing most of the device drives, the kernel offers interfaces for programs to access system hardware such as memory, graphic cards, and block devices.
This article refers exclusively to the Linux kernel and will focus on methods available to obtain, configure, and compile the Linux kernel.
Which kernel to install?
When manually compiling kernel sources or using genkernel to automate some of the process, Gentoo recommends the sys-kernel/gentoo-sources package for most users. Its stable versions follow the long term stable (LTS) kernels from upstream kernel.org.
A newer method of obtaining a kernel is the sys-kernel/gentoo-kernel package, which by default configures the kernel using a Gentoo provided kernel configuration file, then compiles the sys-kernel/gentoo-sources kernel sources through Portage. One advantage to this approach is that the kernel binaries will be updated to newer releases with @world updates. This can lessen administrative attention from system administrators.
For more information on gentoo-kernel see the Distribution kernel project.
Since the gentoo-kernel package automates the configuration and compilation process, this article will continue presuming the gentoo-sources package was selected.
To obtain a kernel, it is necessary to install the kernel source code. The Gentoo recommended kernel sources for a desktop system are, of course, sys-kernel/gentoo-sources. These are maintained by the Gentoo developers, and patched when necessary to fix security vulnerabilities, functional problems, as well as to improve compatibility with rare system architectures.
USE flags for sys-kernel/gentoo-sources Full sources including the Gentoo patchset for the 5.12 kernel tree
||!!internal use only!! DO NOT SET THIS FLAG YOURSELF!, used for creating build images and the first half of bootstrapping [make stage1]|
||Apply experimental patches; for more information, see "https://wiki.gentoo.org/wiki/Project:Kernel/Experimental".|
||Force kernel ebuilds to automatically update the /usr/src/linux symlink|
Now install sys-kernel/gentoo-sources:
emerge --ask sys-kernel/gentoo-sources
Although all stable kernel Gentoo provides is sys-kernel/gentoo-sources, there are many other kernel packages in the Portage tree. See the Kernel sources overview article, which gives details on most of them.
For which to pick, see also the blog article What Stable Kernel Should I Use? by Greg Kroah-Hartman, a major kernel developer.
Searching all kernel packages
A full list of kernel sources with short descriptions can be found by searching with emerge:
emerge --search "%@^sys-kernel/.*sources"
- Automatic configuration
- genkernel is a tool used to automate the build process of the kernel and initramfs. The goal of genkernel is to help users through the kernel building process.
- Manual configuration
- Manual configuration enables the user, with some effort, to create a custom-fit kernel configuration.
- Gentoo kernel configuration guide
- Gentoo's kernel configuration guide.
- Kernel security
- Instructions for securing the kernel.
- Kernel Seeds
- Like the option above, Kernels Seeds help the user, with some effort, create a custom-fit kernel configuration using an existing .config as a base.
- Steps to upgrade to a new kernel using an existing configuration.
- 2.4 to 2.6 Migration
- Migration guide from Linux 2.4 to Linux 2.6. Since the Linux kernel codebase has significantly moved past 2.6, these migration steps are no longer relevant, but may be useful for helping administrators understand.
- Steps to completely remove old kernels.
In-kernel configuration support
See the IKCONFIG support sub-article.
Kernel command-line parameters
When booting from a bootloader, the Linux kernel can accept command-line parameters to change its behavior. This can aid in troubleshooting the kernel at boot time, to blacklist a certain module that should not loading, etc.
Kernel.org has a nicely formatted list of available kernel command-line parameters to review.
Specifically, the following command-line parameters may be helpful when booting Gentoo:
- Project:Distribution Kernel — aims to maintain sys-kernel/*-kernel packages.
- Linux firmware — is a package distributed alongside the Linux kernel that contains firmware binary blobs necessary for partial or full functionality of certain hardware devices.
- LVFS — a daemon that provides a safe, reliable way of applying firmware updates on Linux.
- Kernel/IKCONFIG support — Enabling In-kernel Config (IKCONFIG) support for the Linux kernel enables the inspection of kernel configuration for running kernels.
- The kernel category - All the kernel related articles on the wiki.
- The hardware category - Lists of hardware stacks with associated kernel configurations.
- planet.kernel.org - Blogs related to the Linux kernel.
- kernelnewbies.org - A "community of aspiring Linux kernel developers who work to improve their Kernels and more experienced developers willing to share their knowledge".
- kernel.org/doc/ - Official comprehensible documentation for the Linux kernel.
- What Stable Kernel Should I Use?, written by Greg Kroah-Hartman.
- Building the kernel as root can be harmful