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, the recommended kernel sources are the gentoo-sources. The gentoo-sources package contains various kernel patches, designed to improve user experience with respect to different areas. Speaking of security: you can find support for grsecurity, together with other security enhancements and, naturally, all the recent fixes for known vulnerabilities. The included patches deal also with performance (including tweaks for desktop usage and support for recent hardware) and features (supermount, bootsplash, the latest NTFS drivers, and more).

The gentoo-sources (together with gentoo-dev-sources) absorb 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 2.4 kernel sources released on http://www.kernel.org/, maintained (contrary to popular belief) not by Linus Torvalds himself, but by Marcelo Tosatti. Linus is the leader of active kernel development, but as he is only one man, he passes off the maintenance of the stable 2.4 kernel branch to someone he can trust to handle it once it has stabilized. Thus, Alan Cox became the maintainer of the Linux-2.2 kernel series and Marcelo Tosatti became the maintainer of the Linux-2.4 kernel series. This is what all the other patch sets in the 2.4 series are based on. Marcelo has been doing an outstanding job with its maintenance and it can be counted on for stability and up-to-date (if not bleeding edge) hardware support.

vanilla-sources are probably the most stable sources available since they are the most tested and all possible kernel sources are based on them. If you don't need any of the extras that the other kernels supply then the vanilla-sources are your thing.

The gentoo-dev-sources ebuild includes the most up-to-date 2.6 kernel with Gentoo's optimized performance patches.

The development-sources ebuild provides the stable 2.6 Linux kernel. As opposed to what the name might suggest, this kernel source is completely stable and production-ready. This is the official 2.6 kernel released on http://www.kernel.org/.

For users to whom desktop interactive performance comes as a secondary priority to reliability and hardware support, we have the gs-sources. GS stands for Gentoo Stable (creative, aren't we?). This patch set is tuned and tested to provide the best support for the latest hardware and ensures that your mission critical servers will be up when you need them. This kernel doesn't have some of the most aggressive performance tuning patches from the gentoo-sources, but rest assured, the great performance that you know and love from the vanilla kernels are alive and well. Where possible and without compromising stability we add server related performance patches.

This kernel provides support for the latest ACPI subsystem, EVMS, ECC (required for HA Linux systems), Encrypted Loopback devices, NTFS, Win4Lin and XFS. It also contains updates for IDE, ext3 and several network cards amongst other patches.

In other words, these sources are perfect for servers and High-Availability systems.

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

hardened-sources 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.

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

hardened-dev-sources use the 2.6 kernel with the patches provided by the various subprojects of Gentoo Hardened.

alpha-sources, hppa-sources, hppa-dev-sources, ia64-sources, mips-sources, ppc-sources, pegasos-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. Kernel sources that contains a "-dev-" means that the sources use the 2.6 kernel instead of the 2.4 kernel.

The compaq-sources provide RedHat's kernel sources for Alpha, maintained by Compaq.

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.

First we have aa-sources. This is Andrea Arcangeli's patch set. Andrea is known as an amazing coder by many other kernel hackers. His kernel patch set has some of the most aggressively tuned VM (Virtual Memory) patches known to mankind.

It also provides User Mode Linux support (check out our UML Guide for more information) and the latest TUX Webserver (an in-kernel webserver).

If you have Memory Management troubles with other kernels, aa-sources can be your solution. If you want to optimize Linux's Memory Management for your system, aa-sources is definitely what you need.

Visit http://www.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.6 for more information about all the patches in these kernel sources.

ck-sources is Con Kolivas's kernel patch set. This kernel is HIGHLY tuned for desktop performance at the expense of throughput and some of the scheduler's ability to prioritize applications. Con Kolivas benchmarks kernels to find the best combination of features for desktop use. See http://kernel.kolivas.org for more information on Con and his patches.

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.

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

The pac-sources kernel tree is patched with Bernhard Rosenkraenzer's (bero) patches.

This kernel source contains the Linux Kernel source for the version of the Redhat Linux Kernel modified by the Planet CCRMA (custom audio upgrade) project.

More information can be found at http://ccrma-www.stanford.edu/.

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.