KernelCustomBuild
Disclaimer
Building and using a custom kernel will make it very difficult to get support for your system. You will not be allowed to file bugs on the custom-built kernel (if you do, they will be Rejected without 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 for which you have filed or will file a bug report on the stock Ubuntu kernel.
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. If you hose your box, reinstall. Don't bother asking for help.
You got to this page by mistake, but checked it out because it looked interesting. Believe me, this isn't interesting at all
What you'll need
To start, you will need to install a few packages.
sudo apt-get install linux-kernel-devel fakeroot kernel-wedge kernel-package
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.
How to get the kernel source
There are two ways to obtain the Ubuntu kernel source. The prefered way is to use git. Detailed instructions for using git can be found in KernelGitGuide.
The other way is to simply:
sudo apt-get install linux-source
This will give you the source to the latest available kernel. However, this will almost always be out of date compared to the latest development source. Using git allows you to always stay in sync with the latest Ubuntu kernel source.
Modifying 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 2.6.17, i386:
$ ls -l debian/config/i386/ total 88 -rw-r--r-- 1 me me 62737 Jun 14 18:31 config -rw-r--r-- 1 me me 1859 Jun 12 14:59 config.386 -rw-r--r-- 1 me me 1394 Jun 12 14:59 config.686 -rw-r--r-- 1 me me 1420 Jun 12 14:59 config.k7 -rw-r--r-- 1 me me 1519 Jun 12 14:59 config.server -rw-r--r-- 1 me me 1867 Jun 12 14:59 config.server-bigiron
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.
Note: If you do not find the config files there, you may find them in your /boot directory. For instance:
/boot/config-2.6.15-23-386
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/bin/oldconfig ARCH
Building the kernel
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.
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 fakeroot debian/rules binary-debs flavours=k7
This will only build the AMD k7 variant of the i386 architecture.
The debs are placed in ubuntu-2.6/debian/build.
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].bz2
Now you are in the top directory of a source tree; to configure and ocmpile your kernel simply
make menuconfig make-kpkg --rootcmd fakeroot --initrd --append-to-version=-some-string-here kernel-image kernel-headers
The packages should be placed in ~/.
When it's done
Now that the build is complete, you can install the generated debs using dpkg:
sudo dpkg -i linux-image-2.6.17-2-ef427c-k7_2.6.17-2.2_i386.deb sudo dpkg -i linux-headers--2.6.17-2-ef427c-k7_2.6.17-2.2_i386.deb
If you use modules from linux-restricted-modules, you will need to recompile this against your new linux-headers package. Details on how to do this will be added later.
Linux-Restricted-Modules: the Tough Stuff
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 speerately, 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.
=== 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-2.6.some-version-ubuntu apt-get source linux-restricted-modules-2.6.some-version-ubuntu cd linux-restricted-modules-2.6.something
Mess with debian/rules
-are we supposed to just use module-assistant? any plans to add this info? thanks, MattPrice
Q: What about custom install and netboot images (and their initrd etc)?, PeterMagnusson
A:
Q: What directory are you in when you run these commands ls -l debian/config/i386/ I'm sure you mean to untar the kernel source you just downloaded and cd into that tree (cd /usr/src ; tar xf linux-source-2.6.17.tar.bz2 ; cd linux-source-2.6.17) but there is no directory debian/config/i386 in there. debian/Config has .config files in it, but no bigiron file so i dono where that kernel comes from? EliCriffield
A: Maybe he meant debian/Config?
A2: On 6.06, the linux-source package does not include the debian directory, it seems. You need to install the source package for linux-image, with a command like
sudo apt-get source linux-image-2.6.15-27-386
Q: Is there any way to get a kernel build faster? I would like to do some "light" kernel hacking. What are the easy steps to just compile a kernel image?