UbuntuHelp:Kernel/Compile

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https://help.ubuntu.com/community/Kernel/Compile

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Disclaimer

Building and using a custom kernel will make it very difficult to get support for your system. While it is a learning experience to compile your own kernel, you will not be allowed to file bugs on the custom-built kernel (if you do, they will be Rejected without further explanation). If you have a commercial support contract with Ubuntu/Canonical, this will void such support. Also note that this page describes how to do things for the Edgy (2.6.17) kernel and newer! Until this kernel source, we did not have any mechanisms in place that would allow people to build their own kernels easily. This was intentional. This page does NOT describe how to build stock kernels from kernel.org. This is how to rebuild the actual Ubuntu kernel source.

Reasons for compiling a custom kernel

• You are a kernel developer.
• You need the kernel compiled in a special way, that the official kernel is not compiled in (for example, with some experimental feature enabled).
• You are attempting to debug a problem in the stock Ubuntu kernel for which you have filed or will file a bug report.
• You have hardware the stock Ubuntu kernel does not support.

Reasons for NOT compiling a custom kernel

• You merely need to compile a special driver. For this, you only need to install the linux-headers packages.
• You have no idea what you are doing, and if you break something, you'll need help fixing it. Depending on what you do wrong, you might end up having to reinstall your system from scratch.
• You got to this page by mistake, but checked it out because it looked interesting. Believe me, this isn't interesting at all :)

If you want to install a new kernel without compilation, you can use Synaptic, search for linux-image and select the kernel version you want to install. An easier way is Click on System > Administration > Update Manager > Click on Check button > Apply all updates including kernel.

Tools you'll need

To start, you will need to install a few packages.

sudo apt-get install linux-kernel-devel fakeroot build-essential

This will install the compiler related packages and kernel packaging tools. It will also install the git-core package, which is the best way to interact with the Ubuntu kernel source.

Get the kernel source

There are a few ways to obtain the Ubuntu kernel source:

1. Use git (detailed instructions on it can be found in the Kernel Git Guide) - This allows you to always stay in sync with the latest Ubuntu kernel source.
2. Download the source archive - This is the simplest way and useful to those who want to rebuild the standard Ubuntu packages with additional patches. Note that this will almost always be out of date compared to the latest development source, so you should use git (option #1) if you need the latest patches. In order to download the source archives:

sudo apt-get build-dep linux-source
apt-get source linux-source

For Hardy (8.04) this has changed to:

sudo apt-get build-dep linux-image-$(uname -r)
apt-get source linux-image-$(uname -r)

1.#3 Download the source package (detailed instructions are further down this page under AltBuildMethod Alternate Build Method: The Old-Fashioned Debian Way) - Please be aware this is NOT the same as option #2

Modify the source for your needs

For most people, simply modifying the configs is enough. If you need to install a patch, read the instructions from the patch provider for how to apply. The stock Ubuntu configs are located in debian/config/ARCH/ where ARCH is the architecture you are building for. In this directory are several files. The config file is the base for all targets in that architecture. Then there are several config.FLAVOUR files that contain options specific to that target. For example, here are the files for 2.6.20, i386:

ls -l debian/config/i386/
total 108
-rw-r--r-- 1 root src  73962 2007-08-13 01:29 config
-rw-r--r-- 1 root root  1369 2007-08-13 01:29 config.386
-rw-r--r-- 1 root root  1330 2007-08-13 01:29 config.generic
-rw-r--r-- 1 root root  1395 2007-08-13 01:29 config.server
-rw-r--r-- 1 root root  1756 2007-08-13 01:29 config.server-bigiron
-rw-r--r-- 1 root root     8 2007-08-13 01:25 lowlatency
-rw-r--r-- 1 root root   194 2007-08-13 01:25 vars.386
-rw-r--r-- 1 root root   218 2007-08-13 01:25 vars.server-bigiron

If you do not find the config files under debian/config, you may find them in your /boot directory, for instance, /boot/config-2.6.22-14-generic. If you need to change a config option, simply modify the file that contains the option. If you modify just the config file, it will affect all targets for this architecture. If you modify one of the target files, it only affects that target. After applying a patch, or adjusting the configs, it is always best to regenerate the config files to ensure they are consistent. There is a helper command for this. To regenerate all architectures run:

debian/rules updateconfigs

If you just want to update one architecture, run:

debian/scripts/misc/oldconfig ARCH

Build the kernel (when source is from git repository, or from apt-get source)

To build the kernel(s) is very simple. Depending on your needs, you may want to build all the kernel targets, or just one specific to your system. However, you also want to make sure that you do not clash with the stock kernels. These instructions are specific to the git-tree and for the source downloaded via apt-get source, not when downloading the linux-source package Use this command to build all targets for the architecture you are building on:

AUTOBUILD=1 fakeroot debian/rules binary-debs

The AUTOBUILD environment variable triggers special features in the kernel build. First, it skips normal ABI checks (ABI is the binary compatibility). It can do this because it also creates a unique ABI ID. If you used a git repo, this unique ID is generated from the git HEAD SHA. If not, it is generated from the uuidgen program (which means every time you execute the debian/rules build, the UUID will be different!). Your packages will be named using this ID. To build a specific target, use this command:

AUTOBUILD=1 NOEXTRAS=1 fakeroot debian/rules binary-FLAVOUR

Where FLAVOUR is one of the main flavours of the kernel (e.g. generic) To build one of the custom flavours (found in debian/binary-custom.d/), use:

AUTOBUILD=1 NOEXTRAS=1 fakeroot debian/rules custom-binary-FLAVOUR

As of this documentation, custom flavours include xen and rt. If you have a more than one processor or more than one core, you can speed things up by running concurrent compile commands. Prepend CONCURRENCY_LEVEL=2 for two processors or two cores; replace '2' with whatever number suits your hardware setup (for Gutsy and later, you can alternatively use DEB_BUILD_OPTIONS=parallel=2).

CONCURRENCY_LEVEL=2 AUTOBUILD=1 NOEXTRAS=1 fakeroot debian/rules binary-generic

To trigger a rebuild, remove the appropriate stamp file from debian/stamps (e.g. stamp-build-server for the server flavour, etc.). The debs are placed in your kernel directory's parent directory. Anchor(AltBuildMethod)

Alternate Build Method: The Old-Fashioned Debian Way

The new Ubuntu build system is great for developers, for people who need the absolute latest bleeding-edge kernel, and people who need to build a diverse set of kernels (several "flavours"). However it can be a little complex for ordinary users. If you don't need the latest development sources, there is a simpler way to compile your kernel from the linux-source package. As suggested above, all you need for this is:

sudo apt-get install linux-source
mkdir ~/src
cd ~/src
tar xjvf /usr/src/linux-source-<version-number-here>.tar.bz2
cd linux-source-<version-number-here>

Now you are in the top directory of a kernel source tree. Before building the kernel, you must configure it. If you wish to re-use the configuration of your currently-running kernel, start with

cp -vi /boot/config-`uname -r` .config

Before you run 'make menuconfig' or 'make xconfig' (which is what the next step tells you to do), make sure you have the necessary packages

sudo apt-get install qt3-dev-tools libqt3-mt-dev # if you plan to use 'make xconfig'
sudo apt-get install libncurses5 libncurses5-dev # if you plan to use 'make menuconfig'

Then, regardless of whether you're re-using existing configuration or starting from scratch:

make menuconfig # or "make xconfig" if you prefer

If you re-used the existing configuration, note that Ubuntu kernels build with debugging information on, which makes the resulting kernel modules (*.ko files) much larger than they would otherwise be. To turn this off, go into "Kernel hacking"; then, under "Kernel debugging", turn OFF "Compile the kernel with debug info". Now you can compile the kernel and create the packages:

make-kpkg clean # only needed if you want to do a "clean" build
fakeroot make-kpkg --initrd --append-to-version=-some-string-here kernel-image kernel-headers

The *.deb packages will be created in the parent directory of your Linux source directory (in this example, it would be placed in ~/src because our Linux source directory is ~/src/linux-source-<version-number-here>).

Install the new kernel

If you want to see the ubuntu splash screen (or use text mode) before you get to X instead of just a black screen, you'll want to make sure the framebuffer driver loads:

echo vesafb | sudo tee -a /etc/initramfs-tools/modules
echo fbcon | sudo tee -a /etc/initramfs-tools/modules

Now that you've told initramfs-tools what modules it should include and the build is complete, you can install the generated debs using dpkg:

sudo dpkg -i linux-image-2.6.20-16-2be-k7_2.6.20-16_i386.deb
sudo dpkg -i linux-headers-2.6.20-16-2be-k7_2.6.20-16_i386.deb

If you use modules from linux-restricted-modules, you will need to recompile this against your new linux-headers package.

Rebuilding linux-restricted-modules

The Linux-Restricted-Modules (l-r-m) package contains a number of non-DFSG-free drivers (as well as some firmware and the ipw3945 wireless networking daemon) which, in a perfect world, wouldn't have to be packaged separately, but which unfortunately are not available under a GPL-compatible license. If you use any of the hardware supported by the l-r-m package, you will likely find that your system does not work as well after switching to a custom kernel. In this case you should try to compile the l-r-m package. You will need to install the linux-headers packages that you built in the previous stage.

sudo dpkg -i linux-source-2.6.20-2.6.20/debian/build/linux-headers*.deb

Get the source

First, we make sure we have all the packages necessary to build l-r-m, and then we fetch the source:

sudo apt-get build-dep linux-restricted-modules-common
apt-get source linux-restricted-modules-common
cd linux-restricted-modules-2.6.*

Adjust debian/rules

Debian (and hence Ubuntu) packages are built by calling the the debian/rules script from the top source directory; this script is a specialized Makefile with 'targets' you can call as arguments when you run the script. The l-r-m debian/rules script is geared towards developers working with the official builds and makes certain assumptions about kernel version numbers and what header packages are installed; if you need to build l-r-m on your own, you will need to customize it. The full range of customizations are beyond the scope of this guide, but here are a couple examples of problems you're likely to run into and possible ways to solve them: Kernel Version Mismatch If you built your kernel using one of the recommended methods, your kernel version is probably not precisely what debian/rules expects; for instance, my git-built kernel is called 2.6.19-7-ref-generic instead of 2.6.19-7-generic, while my make-kpkg-built kernel is called 2.6.19-7-suspend2-generic. You can solve this problem by changing this line (the actual value here will be different by the time you read this):

abi_version = 7

to something like this:

abi_version = 7-ref

After making this change, the control file will have to be rebuilt by running:

debian/rules debian/control

Too Many Flavours debian/rules expects you to have the header files for all possible kernel flavours already installed. If you only compiled one kernel flavour, this is of course impossible. So you need to look in debian/rules and change all the "flavours" lines so that only one flavour is listed -- the one you have already compiled. so for instance in my case, working on the i386 architecture:

flavours := $(addprefix $(kernel_abi_version)-,generic, server, lowlatency)

became:

flavours := $(addprefix $(kernel_abi_version)-,generic)

You may find that further modifications are necessary. udebs mess you up The standard "binary" target includes building udebs, which look for flavours that you may not have installed. I did two things:

1. Modified debian/d-i/kernel-versions.in
2. deleted "build-udebs" from the binary target

I'm not sure the latter was necessary, but as you are not likely to need to build any udebs it's probably pretty safe to do. Now cross your fingers and hope! Try to build with:

fakeroot debian/rules binary

Note: you will need around 8 hours of compilation time and around 10 Gb of hard drive space to compile all kernel flavours and a restricted modules.

Speeding Up The Build

Use distcc and, if you're rebuilding often, ccache. A good overview of using distcc on a debian-based system is available at http://myrddin.org/howto/using-distcc-with-debian. If you have AMD64 machines available on your local net, they can still participate in building 32-bit code; distcc seems to handle that automatically. However, with distcc taking over all compiles by default, you will need to set HOSTCC so that when kernel builds want to use the compiler on the host itself, they don't end up distributing jobs to the 64-bit server. If you fail to do that, you'll get link-compatibility failures between 64-bit and 32-bit code. My make-kpkg command, with /usr/lib/ccache at the head of my $PATH, looks like:

MAKEFLAGS="HOSTCC=/usr/bin/gcc CCACHE_PREFIX=distcc" make-kpkg --rootcmd fakeroot --initrd --append-to-version=-suspend2 kernel-image kernel-headers kernel-source

More documentation

• https://help.ubuntu.com/community/forum/software/CustomKernel
• UpgradeKernel , with easier ways.

Comments

Please go to the community wiki page for comments, questions and discussion: https://wiki.ubuntu.com/KernelCustomBuild

External information

• http://www.howtoforge.com/kernel_compilation_ubuntu Compile a kernel from kernel.org source in Ubuntu

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