As with everything else in Gentoo Linux, the philosophy of the Gentoo Kernel team is to give you, the user, as much freedom of choice as possible. If you take a look at the output of emerge -s sources you see a large variety of kernels to choose from. In this document, I will attempt to give you a brief rundown of the goals of each of the patch sets, which we at Gentoo design, and also explain the other kernel sources we make available to you.

Genkernel is a kernel toolset that can be used to autodetect your hardware and configure your kernel automatically. This is usually recommended for users who do not feel comfortable about compiling a kernel manually.

For more information, please read the Gentoo Linux Genkernel Guide.

For most users, we recommend the gentoo-sources kernel. Two different kernel branches exist under this package name: gentoo-sources-2.4 and gentoo-sources-2.6. On most architectures, 2.6 is the default, and we recommend that you choose this branch.

gentoo-sources-2.6 is a kernel based on Linux 2.6, with various kernel patches included to fix security problems, kernel bugs, and to increase compatibility with the more uncommon system architectures. Linux 2.6 is the current official stable kernel tree, and development is progressing rapidly. For highest performance, best hardware support, and its large new feature set, we recommend 2.6 over its older 2.4 counterpart.

Some of the more uncommon system architectures are not fully compatible with Linux 2.6, and some users prefer to the tried-and-tested Linux 2.4 kernel; for this reason we provide gentoo-sources-2.4. The patches included in this kernel are similar to those included in its 2.6 counterpart, plus a number of patches designed to add functionality and improve performance. Linux 2.4 is currently not being developed further - only bug and security fixes are being included in the newer releases. If you are able to, we suggest that you upgrade to Linux 2.6. You may find the migration document useful.

The gentoo-sources package absorbs most of the resources of the Gentoo kernel team. They are brought to you by a group of talented developers, which can count on the expertise of popular kernel hacker Greg Kroah-Hartman, maintainer of udev and responsible for the USB and PCI subsystems of the official Linux kernel.

The next kernel sources that many of you will probably be familiar with as Linux users are the vanilla-sources. These are the official kernel sources released on http://www.kernel.org/. Please note that we do not patch these kernels at all - these are purely for people who wish to run a completely unmodified Linux kernel.

Similarly to gentoo-sources, two versions of Linux can be found under this package: 2.4 and 2.6.

Linux 2.4 is maintained by Marcelo Tosatti. Linus Torvalds, the original creator of Linux, handed maintainership of the Linux 2.4 branch over to Marcelo when Linus went off to start developing the newer 2.6 kernel tree. Marcelo has done a fine job of keeping 2.4 stable and secure, and is now only accepting security and bug fixes into the 2.4 kernel tree. Actual development happens in the Linux 2.6 kernel tree.

Linux 2.6 is maintained by Andrew Morton, who works closely with Linus Torvalds to deliver a fast, powerful, and feature-packed Linux kernel. Development is happening at incredible pace and this kernel tree is now very mature.

hardened-sources is based on Linux 2.4 and is targetted at our users running Gentoo on server systems. It provides patches for the various subprojects of Gentoo Hardened (such as support for LSM/SELinux and GRSecurity), together with stability/security-enhancements. Check http://www.gentoo.org/proj/en/hardened/ for more information.

hardened-dev-sources serves the same purpose as hardened-sources but is based on the newer Linux 2.6 kernel base.

The following USE-flags can be set to select optional patches:

alpha-sources, hppa-sources, hppa-dev-sources, mips-sources, pegasos-dev-sources, sparc-sources and xbox-sources are, as their names suggest, patched to run best on specific architectures. They also contain some of the patches for hardware and features support from the other patch sets mentioned above and below. A "-dev-" in the name of a kernel package means that the sources use the 2.6 kernel instead of the 2.4 kernel.

Now I'm going to try to briefly describe some of the other sys-kernel/*-sources which you saw scroll by when you ran emerge -s sources. Lets take them in alphabetical order. These kernels are provided as a courtesy only and the various patch sets are not supported by the Gentoo team.

ck-sources is Con Kolivas's kernel patch set. This patchset is primarily designed to improve system responsiveness and interactivity and is configurable for varying workloads (from servers to desktops). The patchset is also quite mature and has been put through numerous iterations of development and tuning. The emphasis of each release is on stability and security. Support and information is available at http://kernel.kolivas.org and in #ck on irc.oftc.net.

The grsec-sources kernel source is patched with the latest GRSecurity updates (GRSecurity version 2.0 and up) which includes, amongst other security-related patches, support for PaX.

The mm-sources are based on the development-sources and contain Andrew Morton's patch set. They include the experimental and bleeding-edge features that are going to be included in the official kernel (or that are going to be rejected because they set your box on fire). They are known to be always moving at a fast pace and can change radically from one week to the other; kernel hackers use them as a testing ground for new stuff.

If you really want to live on the edge and you think development-sources are for wussies, then try out mm-sources. Be warned that this kernel is highly experimental and doesn't always work as expected.

The openmosix-sources are patched to support the openMosix system (like MOSIX but Open Source). For more information see http://www.openmosix.org.

selinux-sources from http://www.nsa.gov/selinux are patches for the security conscious to support the LSM (Linux Security Modules) and the Flask Security Architecture.

usermode-sources are the User Mode Linux kernel patches. This kernel is designed to allow Linux to run within Linux to run within Linux to ... User Mode Linux is intended for testing and virtual server support. For more information about this amazing tribute to the stability and scalability of Linux, see http://user-mode-linux.sourceforge.net.

For more information on UML and Gentoo, read the Gentoo UML Guide.

win4lin-sources are patched to support the userland win4lin tools that allow Linux users to run many Microsoft Windows (TM) applications at almost native speeds. See http://www.netraverse.com/ for more information.

wolk-sources contains the Working Overloaded Linux Kernel from http://sourceforge.net/projects/wolk. This kernel contains many patches of a wide variety, all combined into the kernel with extreme care. This allows you to configure nearly every one into and out of the kernel at compile time -- so the kernel will work with nearly any combination of the patches.

If you need a certain combination of patches that you cannot find in other kernel sources, WOLK is definitely worth a shot.

aa-sources was a heavily modified kernel with all kinds of patches. The upstream maintainer has stopped releasing kernel patchsets, this package was removed as it went out of date.

alpha-sources was a 2.4 kernel with patches applied to improve hardware compatibility for the Alpha architecture. These patches have been developed and included in the mainline kernel. Alpha users can now run any recent kernel with no need for extra patches.

development-sources, the official 2.6 kernel from kernel.org, can now be found under the vanilla-sources package.

gentoo-dev-sources, a 2.6 kernel patched with bug, security and stability fixes, can now be found under the gentoo-sources package.

The rsbac-dev-sources kernels can now be found under the rsbac-sources package.

selinux-sources, a 2.4 kernel including lots of security enhancements, has been obseleted by security development in the 2.6 tree.