Funtoo Linux Kernels

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This Section will give you an overview of kernels used in funtoo.

Funtoo Linux provides a number of new kernels for your use. This is the official page for all Funtoo Linux kernel information.

Some points of interest:

  • Most Funtoo Linux kernels support the handy binary USE flag, described below.
  • Funtoo Linux offers quality kernels from other Linux Distributions, like ubuntu-server and debian-sources.
  • A detailed Kernel Features and Stability table can be found below.
  • Advanced users may want to take a look at Additional Kernel Resources.
  • There is a quick'n dirty howto to compile your own kernel with initramfs the funtoo way.

Overview of Kernels


This kernel is from the SystemRescueCD project, and is based on Fedora 14/15, plus some other patches related to booting from a live CD. It is a quality kernel, and is generally pretty stable. It is not suitable for production servers but is a good choice for Funtoo Linux desktops. Earlier,the Funtoo Linux Installation Guide recommended this kernel for general users, but now 'debian-sources' is recommended. Note however, that by design all audio functions are removed from SystemRescue, ie no sound when using this kernel.


This will install the "vanilla" (unmodified) Linux kernel sources. Current recommended version is 3.x. Funtoo Linux fully supports Linux 3.x. The advantages of this kernel include recent improvements to Linux Containers, a very modern networking stack with lots of bug fixes, and high reliability for desktops and servers. The downside is that this kernel must be manually configured by the user and does not have built-in genkernel support via the binary USE flag at this time.


This kernel tree is based on stable kernels from with genpatches applied genpatches. Gentoo patchset aims to support the entire range of Gentoo-supported architectures. List of available genpatched kernels: genpatches-kernels


This is a RHEL6-based kernel with OpenVZ support. This kernel is now the preferred kernel for production OpenVZ deployments. It requires gcc-4.4.5 to build, which it will use automatically without the user needing to use gcc-config. We use this version of gcc since this is the version of gcc used by Red Hat to build this kernel.


This kernel is based on the latest Red Hat Enterprise Linux 5.6 kernel, and contains additional OpenVZ (virtual containers) patches from the OpenVZ project. It is a very stable and reliable kernel, and is recommended for use in production environments. The only major downside to this kernel is that it is based on Linux 2.6.18 -- some parts of the kernel are out-of-date, and it is not compatible with modern versions of udev. However, it is pretty trivial to downgrade udev to an earlier version on Funtoo Linux and this kernel has a track-record of being rock-solid. When stability is paramount, you put up with the udev downgrade, use this kernel, and can enjoy hundreds of days of uptime. For more information on how to use this kernel with Funtoo Linux, see the RHEL5 Kernel HOWTO.


This is the kernel from Ubuntu Server. Version is the same version used in Ubuntu Server 10.04 LTS, and version is the one used in Ubuntu Server 10.10 (currently masked). In our testing of, it has been very reliable and offers very good performance. One exception, which is common among 2.6.32-based kernels, is that it's recommended that you emerge broadcom-netxtreme2 if you have any Broadcom-based NICs, as the in-kernel drivers have compatibility issues with certain models. This kernel is a very good option if you want a relatively modern server kernel and do not need OpenVZ support. We use gcc-4.4.5 to build this kernel. It will use gcc-4.4.5 automatically, without requiring the user to use gcc-config.


This is the Debian kernel. These ebuilds now support the binary USE flag. Daniel has added a special config-extract command which can be used to list all available official Debian kernel configurations, and generate them from the Debian files included with the kernel. This kernel has optional OpenVZ support, but it is much better to use openvz-rhel6-stable if you want a production-quality OpenVZ installation. For more information about how to use debian-sources and config-extract, see Using debian-sources with Genkernel below.


This is the Debian long-term stable kernel. These ebuilds now support the binary USE flag. Daniel has added a special config-extract command which can be used to list all available official Debian kernel configurations, and generate them from the Debian files included with the kernel.

Binary USE

Many of the kernel ebuilds in Funtoo Linux support the very useful binary USE flag. By enabling this USE flag and emerging the kernel, the ebuild will automatically build a binary kernel image, initramfs and kernel modules and install them to /boot. The binary kernel image and initramfs can be used to boot your Funtoo Linux system without requiring any additional configuration. This is a great way to get a Funtoo Linux system up and running quickly. Here's how to do it:

# echo "sys-kernel/openvz-rhel5-stable binary" >> /etc/portage/package.use
# emerge openvz-rhel5-stable
# nano -w /etc/boot.conf
# boot-update

More information can be found in the Funtoo Linux Installation Guide.

Funtoo Linux Genkernel

Funtoo Linux contains a forked/enhanced version of genkernel with the following new capabilities:

  • genkernel can use a build directory that is separate from the kernel source directory. This is enabled using the new --build-dst option.
  • --build-src is a new option that is equivalent to the --kerneldir option.
  • --fullname can be used to specify the entire name of the kernel and initramfs images -- everything after kernel- and initramfs-.
  • --firmware-src - a new option that works identically to --firmware-dir.
  • --firmware-dst - a new capability - you can now define where genkernel installs firmware.
  • Genkernel uses Funtoo Linux lvm2 rather than building its own.
  • Some compile fixes.

Kernel Features and Stability

This page provides an overview of kernel features and stability information:

Kernel Name Version USE flags Stability Extra Features Req'd udev Notes
vanilla-sources 3.11.4 N/A Excellent - recommended for desktops and servers. N/A Any Recommended for modern networking stack, hardware and Linux Containers support. This kernel must be manually configured by the user. New Features: New Drivers: kernelnewbies/Linux_3.11-DriversArch
gentoo-sources 3.11.4 N/A Excellent - recommended for desktops and workstations N/A Any Recommended for modern networking stack, hardware and Linux Containers support. This kernel must be manually configured by the user. New Features: New Drivers: kernelnewbies/Linux_3.11-DriversArch
sysrescue-std-sources binary Good - recommended for desktops N/A Any Nvidia card users: binary use flag installs nouveau drivers. Not compatible with nvidia-drivers.
openvz-rhel6-stable binary Excellent - recommended for production servers N/A Any This kernel is built with gcc-4.4.5. emerge broadcom-netxtreme2 for reliable BCM5709+ support (integrated NIC)
openvz-rhel5-stable binary Excellent - recommended for production servers OpenVZ =sys-fs/udev-146* Broadcom bnx2 driver module bundled with kernel appears to be OK. This kernel is built with gcc-4.1.2. Enabling the binary USE flag will cause gcc-4.1.2 to be emerged and used for building the kernel.
ubuntu-server binary Excellent - recommended for production servers (still in extended testing) N/A Any This kernel is built with gcc-4.4.5. emerge broadcom-netxtreme2 for reliable BCM5709+ support (integrated NIC)
ubuntu-server binary not yet tested N/A Any This kernel is built with gcc-4.4.5. emerge broadcom-netxtreme2 for reliable BCM5709+ support (integrated NIC)
debian-sources 3.2.51 openvz Good - default kernel recommended by Funtoo OpenVZ (optional) Any See #Using debian-sources with Genkernel, below.

Using Debian-Sources with Genkernel


Debian-sources is now fully compatible with binary USE flag and recommended for desktop users. The below example is valid for manual installation. At least 12G of /var/tmp required to build

This section describes how to build a binary kernel with debian-sources and genkernel, and it also explains how to use Funtoo Linux's config-extract tool to list and create official Debian kernel configurations.

First step: emerging the required packages

The first step is to emerge:

  1. The Debian sources
  2. Genkernel itself

This is achieved with:

# emerge sys-kernel/debian-sources sys-kernel/genkernel

Once the Debian kernel sources are deployed, you should find a directory named linux-debian-version (e.g. linux-debian- under /usr/src. Update your the linux symlink to point on this directory:

# cd /usr/src
# rm linux
# ln -s linux-debian- linux

Alternatively, emerge the debian-sources with USE="symlink"

Second step: Grabbing a configuration file

If is now time to download the kernel configuration file. For this tutorial we will use a configuration file for AMD64 (several others architectures like MIPS or SPARC64 are available.) To view a complete list of available kernel configurations, type ./config-extract -l in the Debian kernel source directory:

ninja1 linux-debian- # ./config-extract -l

====== standard featureset ======

       alpha: alpha-generic, alpha-legacy, alpha-smp
       armel: iop32x, ixp4xx, kirkwood, orion5x, versatile
        hppa: parisc, parisc-smp, parisc64, parisc64-smp
        i386: 486, 686, 686-bigmem, amd64
        ia64: itanium, mckinley
        m68k: amiga, atari, bvme6000, mac, mvme147, mvme16x
        mips: 4kc-malta, 5kc-malta, r4k-ip22, r5k-ip32, sb1-bcm91250a, sb1a-bcm91480b
      mipsel: 4kc-malta, 5kc-malta, r5k-cobalt, sb1-bcm91250a, sb1a-bcm91480b
     powerpc: powerpc, powerpc-smp, powerpc64
        s390: s390x, s390x-tape
         sh4: sh7751r, sh7785lcr
       sparc: sparc64, sparc64-smp
     sparc64: sparc64, sparc64-smp

====== vserver featureset ======

        i386: 686, 686-bigmem
        ia64: itanium, mckinley
     powerpc: powerpc, powerpc64

====== xen featureset ======


====== openvz featureset ======


Type config-extract -h for extended usage information:

ninja1 linux-debian- # ./config-extract -h
This work is free software.

Copyright 2011 Funtoo Technologies. You can redistribute and/or modify it under
the terms of the GNU General Public License version 3 as published by the Free
Software Foundation. Alternatively you may (at your option) use any other
license that has been publicly approved for use with this program by Funtoo
Technologies (or its successors, if any.)

usage: config-extract [options] arch [featureset] [subarch]

  -h  --help        print this usage and exit
  -l  --list        list all available kernel configurations
  -o  --outfile     specify kernel config outfile --
                    defaults to .config in current directory
  [featureset]      defaults to "none" if not specified
  [subarch]         defaults to the only one available; otherwise required

This program was written by Daniel Robbins for Funtoo Linux, for the purpose of
easily and conveniently extracting Debian kernel configurations. To see a nice
list of all available kernel configurations, use the --list option.

Debian's kernel configs are specified internally in arch_featureset_flavor
format, such as: "amd64_openvz_amd64". The featureset typically describes an
optional kernel configuration such as "xen" or "openvz", while the flavor in
Debian terminology typically refers to the sub-architecture of the CPU.

When using this command, you must specify an arch. A featureset of "none" is
assumed unless you specify one, and by default this program will pick the only
available subarch if there is only one to choose from. If not, you will need to
pick one (and the program will remind you to do this.)

The kernel configuration will be written to ".config" in the current directory,
or the location you specified using the -o/--outfile option.

Let's use config-extract to create a kernel configuration for an amd64 system:

# cd linux
# ./config-extract amd64
Wrote amd64_none_amd64 kernel configuration to /usr/src/linux-debian-

config-extract also allows you to extract special Debian featuresets, such as settings for Xen and OpenVZ kernels:

# ./config-extract amd64 openvz
Wrote amd64_openvz_amd64 kernel configuration to /usr/src/linux-debian-

It is necessary to name the kernel configuration file something other than ".config" to avoid errors with genkernel.

After using config-extract, run make oldconfig and accept all default options by hitting Enter at all prompts.

Third step: Building and installing the kernel

This is simply achieved by:

# genkernel --kernel-config=config-2.6.32-5-amd64 all
  • --kernel-config: use the given configfile. If you only give a filename here, it is searched for in your current working dir. You can also use a relative or an absolute path leading to your configfile here (for example: "--kernel-config=/usr/src/linux/configfile").
  • all: rebuild the kernel image and the initramfs ramdisk image (aside of kernel modules, the ramdisk image contains tools such as BusyBox and some generic startup scripts, depending on options you use on the command line several additional tools like lvm or raid volume management can be incorporated as well).

Unless explicitly stated via --no-clean or --no-mrproper, Genkernel will do a make mrproper in the kernel source tree, thus cleaning a previous build and removing the previous kernel configuration file in it.

If you use Genkernel to rebuild a Linux kernel on SPARC64, remember to either:

  • Set sparc64-unknown-linux-gnu- in General setup --> Cross-compiler tool prefix
  • Put --kernel-cross-compile=sparc64-unknown-linux-gnu- on the Genkernel command line

Once the kernel has been compiled and the ram disk has been generated, the kernel image plus its companion files (initramfs image and are placed in the /boot directory. You can use your favourite tool to update your bootloader configuration files.