Creating a Custom Package of Kernel and Modules

Note: This tutorial assumes that you know how to compile a kernel already. It only looks at a way of creating a package and doesn't aim to show kernel config options.

For info on compiling please look at these pages:

Note2: I will be assuming x86 here, but if anyone wants to contribute some notes on x86_64 until I can get a machine setup, please do.

Kernel Output Target Option

The usual way to make any sort of package is via the $DESTDIR variable. The kernel doesn't use this however, but it does have an O switch which does the same thing, although the output might not be exactly what you expect.

The first job is to create an output directory. I will be using /tmp/kernel-build for this so mkdir it now.

Output Into a Build Directory

From your kernel source directory do

  make O=/tmp/kernel-build menuconfig

(or whichever method you prefer.)

  make mrproper

This will delete your .config in the source tree so make sure you have a copy of it somewhere for safe keeping.

Next steps are the same as a normal make and modules_install, but again using the O= switch:

  make O=/tmp/kernel-build
  make O=/tmp/kernel-build modules_install

Note: Do not use 'make install' as this *will* install it in /boot rather than our build directory.

At this point everything we need is in the build directory. However, taking a look inside it shows many more things have been placed there than we need. The kernel is in arch/x86/boot/ as usual and the modules are in various directories. Luckily for us there is a file, modules.order, which lists the modules to be installed and that we can use to help us make a package.

Installing Modules and Kernel to our Package Directory

Ok let's use /tmp/kernel-package for our package directory. Also let's assume a 2.6.29.6 kernel with jabberwok as local name. A little bash will copy our modules to it:

  for i in $(cat modules.order | sed "s#^kernel/##")
  do
    mkdir -p /tmp/kernel-package/lib/modules/2.6.29.6-jabberwok/$(dirname $i)
    install -m 644 -v $i /tmp/kernel-package/lib/modules/2.6.29.6-jabberwok/$(dirname $i)
  done

Now we need the kernel and associated files.

  mkdir /tmp/kernel-package/boot
  cp arch/x86/boot/bzImage /tmp/kernel-package/boot/vmlinuz-2.6.29.6-jabberwok
  cp System.map /tmp/kernel-package/boot/System.map-2.6.29.6-jabberwok
  cp .config /tmp/kernel-package/boot/config-2.6.29.6-jabberwok

And then the doinst.sh and slack-desc.

  mkdir /tmp/kernel-package/install
  echo "/sbin/depmod -a" > /tmp/kernel-package/install/doinst.sh

I'll leave you to figure out the slack-desc. It should be copied into the install/ directory and appname ought to be (going by this example) kernel-jabberwok.

Making the Package

  cd /tmp/kernel-package
  /sbin/makepkg -l y -c n /tmp/kernel-jabberwok-2.6.29.6_tag-i686-1.txz

Change '_tag' to your usual moniker. Hopefully we now have a package in /tmp. Copy it to a temporary directory somewhere, explodepkg it and check the contents. We don't want to install something with messed up paths etc. If all is well we can installpkg it.

As usual, edit your /etc/lilo.conf and add an option for the new kernel, keeping the old kernel entry in place for safety, then run lilo.

A Little Automation

Of course this would be easier to control with a script rather than typing in these commands manually and trying not to make typos. Here is the script that I've been using:

  #!/bin/bash

  KARCH=${ARCH:-i486}
  ARCH=x86
  MODULELIST=modules.order
  PRGNAM=kernel
  VERSION=${VERSION:-2.6.29.6}
  BUILD=${BUILD:-1}
  TAG=${TAG:-_daw}
  LOCALNAME=${LOCALNAME:-jabberwok}
  OUTPUT=${TMP:-/tmp}
  KOUTPUT=$OUTPUT/$PRGNAM-$LOCALNAME
  PKG=$OUTPUT/$PRGNAM-$LOCALNAME-$VERSION
  MODDIR=$PKG/lib/modules/$VERSION-$LOCALNAME
  set -e

  rm -rf $KOUTPUT
  rm -rf $PKG 
  mkdir -p $KOUTPUT

  cd $SOURCE
  make O=$KOUTPUT menuconfig
  make mrproper
  make O=$KOUTPUT 
  make O=$KOUTPUT modules_install

  cd $KOUTPUT
  for i in $(cat $MODULELIST | sed "s#^kernel/##")
  do
     mkdir -p $MODDDIR/$(dirname $i)
     install -m 644 -v $i $MODDDIR/$(dirname $i)
  done

  mkdir -p $PKG/boot
  cp arch/x86/boot/bzImage $PKG/boot/vmlinuz-$VERSION-$LOCALNAME
  cp System.map $PKG/boot/System.map-$VERSION-$LOCALNAME
  cp .config $PKG/boot/config-$VERSION-$LOCALNAME

  mkdir $PKG/install
  echo "/sbin/depmod -a" > $PKG/install/doinst.sh

  cat << EOF > $PKG/install/slack-desc
  # HOW TO EDIT THIS FILE:
  # The "handy ruler" below makes it easier to edit a package description.  Line
  # up the first '|' above the ':' following the base package name, and the '|'
  # on the right side marks the last column you can put a character in.  You must
  # make exactly 11 lines for the formatting to be correct.  It's also
  # customary to leave one space after the ':'.

  $PRGNAM-$LOCALNAME|-----handy-ruler------------------------------------------------------|
  $PRGNAM-$LOCALNAME: kernel and modules 2.6.29.6-jabberwok
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME: Jabberwokky type kernel!
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME:
  $PRGNAM-$LOCALNAME:
  EOF

  cd $PKG
  /sbin/makepkg -l y -c n $OUTPUT/$PRGNAM-$LOCALNAME-$VERSION$TAG-$KARCH-$BUILD.${PKGTYPE:-tgz}

And here's a downloadable version: http://www.dawoodfall.net/slackbuilds/13.0/kernel/kernel-jabberwok.SlackBuild

Conclusion

The aim for doing this was to be able to build a kernel for my old T42 on my desktop box using the T42's .config. It could be possible to split up kernel and modules into separate packages but I'll let you figure out the details. Note that this does not include the firmware so you should keep the relevant kernel-firmware package installed.

At the end of the day, this helped me to compile a kernel without my laptop getting even warm, which was the point of the project.

--Dive 04:31, 11 March 2010 (UTC)

Kernel-packaging

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