Building custom kernel packages

(this wiki page should be renamed/moved to better reflect the actual content)

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

?Anchor(reasons) 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. Modifying the Debian configuration to change to Pata.

  4. Add a patch fix.
  5. 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.

?Anchor(add-a-patch)

Add a patch to linux-2.6 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-2.6
  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-2.6
    cd linux-2.6-*

    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-2.6_2.6.24~rc6.orig.tar.gz
    cd linux-2.6-*
    svn export svn://svn.debian.org/svn/kernel/dists/trunk/linux-2.6/debian
  3. Start a new stanza at the top of debian/changelog and use an appropriate version number. 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". You could do this with the dch tool from the devscripts package like so:

    dch --local +foo.
  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-2.6.xx-y+foo.1-zzz.

  5. Put your patch into the debian/patches directory and add it to the series file (assuming debian/patches/series/1 is the latest file in there):

    cp ~/special-fix.patch debian/patches/bugfix/
    echo "+ bugfix/special-fix.patch" >> debian/patches/series/1+foo.1
    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
  1. Document the addition of this patch in the new stanza in debian/changelog.

?Anchor(build-all)

  1. 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-2.6-2.6.24~rc6$ debuild -e DEBIAN_KERNEL_JOBS=${NR_CPUS}

?Anchor(build-one)

Building only a single kernel variant

  1. Prepare the rules file for the one build you want to make:

    fakeroot make -f debian/rules.gen setup_i386_none_k7

    This presumes you are only interested in building a k7 AMD processor image! If you were interested in a 686 processor image do:

    fakeroot make -f debian/rules.gen setup_i386_none_686

    This will build a tree in the debian/build/build-i386-none-k7 or debian/build/build-i386-none-686 directory. Go to that directory.

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

    make menuconfig
  3. 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 either:

    fakeroot make -f debian/rules.gen binary-arch_i386_none_k7 binary-indep \
    DEBIAN_KERNEL_JOBS=${NR_CPUS}

    or

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

    On a 2.0GHz CPU the compile will take 1 hour and 20 minutes and 8 package files will be generated, e.g.:

    linux-image-2.6.24-1+foo.1-686_2.6.24-5+foo.1_i386.deb
    linux-headers-2.6.24-1+foo.1-686_2.6.24-5+foo.1_i386.deb
    linux-support-2.6.24-1+foo.1-686_2.6.24-5+foo.1_i386.deb
    linux-tree-2.6.24_2.6.24-5+foo.1_i386.deb
    linux-patch-debian-2.6.24_2.6.24-5+foo.1_i386.deb
    linux-source-2.6.24_2.6.24-5+foo.1_i386.deb
    linux-manual-2.6.24_2.6.24-5+foo.1_i386.deb
    linux-doc-2.6.24_2.6.24-5+foo.1_i386.deb

    Problem: In this case, linux-headers-2.6.24-1+foo.1-common will be missing. One needs to invoke the binary-arch_i386 target, which will yield all feature sets (Xen, VServer) and flavours to be generated, and obviously takes a lot longer. See [http://lists.debian.org/debian-kernel/2008/04/msg00190.html this thread].

The story of linux-kbuild-2.6

The linux-headers-* packages created with the above method depend on linux-kbuild-*, which is a not built from the linux-2.6 source package, but from linux-kbuild-2.6.

Often, when a new kernel comes around, linux-kbuild-2.6.xx isn't yet available in the archive, so you either have to build it yourself, or wait.

How to build linux-kbuild-2.6 yourself

Fetch the sources from SVN:

svn co svn://svn.debian.org/kernel/dists/trunk/linux-kbuild-2.6

Then, fetch the vanilla kernel tarball (important: the 2.6.x version, no 2.6.x.y version):

wget http://ftp.de.kernel.org/pub/linux/kernel/v2.6/linux-2.6.27.tar.bz2

Now, you can prepare the package:

cd linux-kbuild-2.6
./debian/bin/genorig.py ../linux-2.6.27.tar.bz2
cd ..
tar xzf orig/linux-kbuild-2.6_2.6.27.orig.tar.gz
cd linux-kbuild-2.6-2.6.27/
cp -a ../linux-kbuild-2.6/* ./
./debian/bin/gencontrol.py
dch -i

Now adjust the version, and add a comment like "New upstream version" or something, and build the package itself, after you installed eventually missing build-dependencies:

make -f debian/rules clean
dpkg-checkbuilddeps
dpkg-buildpackage -us -uc

and you are done.