Building custom kernel packages

This page is about rebuilding an official Debian kernel package with custom changes. There is the Kernel Handbook about this: http://kernel-handbook.alioth.debian.org/ (which explains how to "Rebuild an official Debian linux kernel package", hopefully : http://kernel-handbook.alioth.debian.org/ch-common-tasks.html ch 4.2 : "Rebuilding an official Debian kernel package").

We are following section 4.2: Rebuilding an official Debian kernel package

Reasons to do this:

1. Modifying the Debian configuration to change the preemption model.

2. Modifying the Debian configuration to change the timer frequency.

3. Add a patch fix.
4. Add your favorite patchset.

What you'll get is exactly the kernel that Debian releases but with those added changes. The new packages will not step on the official kernel images' toes.

Add a patch to linux and build new kernel packages

1. Create the directory where you will build the kernel package as a normal user and make sure you have all necessary packages installed:

   apt-get install fakeroot build-essential devscripts
   apt-get build-dep linux

2. Get the package source. For this to work, you need to have deb-src lines for the official archive in /etc/apt/sources.list:

   apt-get source linux
   cd linux-*

   Now you are in the tree that holds the source and all changes Debian made to it. As an alternative, you could get a kernel tarball, e.g. from buildserver (see DebianKernel), unpack it, and get the latest Debian patches + config settings:

   tar xzf linux_3.0.0~rc6.orig.tar.gz
   cd linux-*
   svn export svn://svn.debian.org/svn/kernel/dists/trunk/linux/debian

3. Look at the top of debian/changelog and think of an appropriate version number. You cannot dch yet, though. If you are adding a single patch "foo", you might want to append "+foo.1". If you are adding multiple patches for your company or yourself, use "+somename.1".

4. Append the same string to the abi.abiname field in debian/config/defines to ensure that your custom kernel package name doesn't bite with the official ones. In our case, we're now creating linux-image-3.x.0-y+foo.1-zzz.

5. Use quilt to add your patch

6. Optional : If it's not the first build attempt, and should you need to clean things in case of build failures :

   make -f debian/rules clean

7. Now check that your patchset still applies and fix any conflicts: Note: on the first run, the target fails. Make sure you run it twice.

   This target is made to fail intentionally, to make sure
   that it is NEVER run during the automated build. Please
   ignore the following error, the debian/control file has
   been generated SUCCESSFULLY.

   make -f debian/rules source-all

8. Now that the above error message has occured after the first “debian/rules clean”, dch will work because debian/control has been (re-)generated. (Note that, after editing debian/changelog, “debian/rules clean” must again be run because its hash changes.) Start a new stanza at the top of debian/changelog and use an appropriate version number. Ensure that the distribution is not set to the regular release names. Change it to something like UNRELEASED. You could do this with the dch tool from the devscripts package like so:

   dch --local +foo.

9. Document the addition of this patch in the new stanza in debian/changelog.

Building all kernel-related packages

1. Make sure you have at least 40 GB of disk space free (version 2.6.32-17 took 30 GB).

2. Assuming you want to build all kernel-related packages, build with the appropriate DEBIAN_KERNEL_JOBS parameter (the number of processors you can use for the build):

   ~/src/linux-3.2.31$ debuild -e DEBIAN_KERNEL_JOBS=${NR_CPUS}

If you plan to do multiple rebuilds you might want to use ccache by adding the --prepend-path=/usr/lib/ccache option to the above debuild command.

Building only a single kernel variant

1. Make sure you have at least 10 GB of disk space free (setup_amd64_none_amd64 took 7.3 GB in version 2.6.32-17).

2. Prepare the rules file for the one build you want to make, e.g.:

   fakeroot make -f debian/rules.gen setup_i386_none_686-pae

   This will build a tree in the debian/build/build_i386_none_686-pae directory. Go to that directory.

3. Change the .config file, using e.g.

   make menuconfig
   cd ../../..

4. Compile the kernel and generate the kernel packages. Replace $NR_CPUS with the number of CPUs of the build machine (keeping it all on the same line) and run e.g.

   fakeroot make -f debian/rules.gen binary-arch_i386_none_686-pae binary-indep \
   DEBIAN_KERNEL_JOBS=${NR_CPUS}

   Some time later the package files will be generated, e.g.:

   linux-image-3.2.0-4+foo.1-686-pae_3.2.31-1+foo.1_i386.deb
   linux-image-3.2.0-4+foo.1-686-pae-dbg_3.2.31-1+foo.1_i386.deb
   linux-headers-3.2.0-4+foo.1-686-pae_3.2.31-1+foo.1_i386.deb
   xen-linux-system-3.2.0-4+foo.1-686-pae_3.2.31-1+foo.1_i386.deb

   Problem: In this case, linux-headers-3.2.0-4+foo.1-common will be missing. One needs to invoke the binary-arch_i386 target, which will yield all feature sets (RT) and flavours to be generated, and obviously takes a lot longer. See this thread. Solution:

   fakeroot make -f debian/rules.gen binary-arch_i386_none_real

5. If you apply further changes to the source package and need to rebuild the binary packages without rebuilding each and every binary objects, you can remove the build stamp before running the above mentioned building command. e.g.

   rm debian/stamps/build_i386_none_686-pae_plain

The story of linux-tools

The linux-headers-* packages created with the above method depend on linux-kbuild-*, which is a not built from the linux source package, but from linux-tools.

Often, when a new kernel comes around, linux-kbuild-3.xx isn't yet available in the archive, so you either have to build it yourself, or wait.

A Mini-Howto from Sedat (dileks) gives detailed instructions how to build linux-kbuild-3.5. An integration here would blow-up this wiki unnecessarily.

How to build linux-tools yourself

Checkout the source from SVN repository:

svn co svn://svn.debian.org/kernel/dists/trunk/linux-tools

Then, download the vanilla kernel tarball (usually the 3.x version, no 3.x.y version):

VERSION="3.6"
wget http://ftp.de.kernel.org/pub/linux/kernel/v3.x/linux-${VERSION}.tar.bz2

Now, you prepare the Debian package:

cd linux-tools
./debian/bin/genorig.py ../linux-${VERSION}.tar.bz2
cd ..
tar -xzf orig/linux-tools_${VERSION}.orig.tar.gz
cd linux-tools-${VERSION}
cp -a ../linux-tools/* ./
./debian/bin/gencontrol.py

NOTE: Optionally, you have to change Debian-version in debian/changelog if $VERSION of Linux-kernel is higher, think of 3.5 (latest version in linux-tools SVN-branch) is smaller than 3.6-rcX (version of tarball), otherwise the genorig.py line fails.

Finally, adjust the Debian version and add comments like "Non-maintainer upload" plus "New upstream version" via dch command. Last but not least, build the package itself after you installed eventually missing build-dependencies:

dch -i
make -f debian/rules clean
dpkg-checkbuilddeps
cp -av ../orig/linux-tools_${VERSION}.orig.tar.gz ../ <--- Necessary to get a diff file.
dpkg-buildpackage -us -uc (or debuild)

and you are done.

• CategoryKernel