Circumvent debootstrap

When building Debian based images KIWI NG uses two tools to create the image root tree. First it calls debootstrap to initialize a minimal root tree and next it chroot’s into that tree to complete the installation via apt. The reason why it is done that way is because apt does not(yet) support to install packages into an empty root directory like it is done with all other packagemanager interfaces implemented in KIWI NG.

The use of debootstrap comes along with some prerequisites and limitations:

  • It can only use one repository to bootstrap from

  • It can only use an official archive repo

  • It has its own dependency resolver different from apt

If one ore more of this properties turns into an issue, KIWI NG allows for an alternative process which is based on a prebuilt bootstrap-root archive provided as a package.

To make use of a bootstrap_package, the name of that package needs to be referenced in the KIWI NG description as follows:

<packages type="bootstrap" bootstrap_package="bootstrap-root">
    <package name="a"/>
    <package name="b"/>

The boostrap process now changes in a way that the provided bootstrap_package bootstrap-root will be installed on the build host machine. Next KIWI NG searches for a tar archive file /var/lib/bootstrap/bootstrap-root.ARCH.tar.xz, where ARCH is the name of the host architecture e.g x86_64. If found the archive gets unpacked and serves as the bootstrap root tree to begin with. The optionally provided additional bootstrap packages, a and b in this example will be installed like system packages via chroot and apt. Usually no additional bootstrap packages are needed as they could all be handled as system packages.

How to Create a bootstrap_package

Changing the setup in KIWI NG to use a bootstrap_package rather then letting debootstrap do the job comes with the task to create that package providing the bootstrap root tree. There are more than one way to do this. The following procedure is just one example and requires some background knowledge about the Open Build Service OBS and its KIWI NG integration.

  1. Create an OBS project and repository setup that matches your image target

  2. Create an image build package

    osc mkpac bootstrap-root
  3. Create the following file

    <image schemaversion="7.4" name="bootstrap-root">
        <description type="system">
            <author>The Author</author>
            <specification>prebuilt bootstrap rootfs for ...</specification>
            <type image="tbz"/>
        <repository type="rpm-md">
            <source path="obsrepositories:/"/>
        <packages type="image">
            <!-- packages included so OBS adds it as a build dependency, however this is installed by debootstrap -->
            <package name="mawk"/>
        <packages type="bootstrap">
            <!-- bootstrap done via debootstrap -->
    osc add
    osc ci
  4. Package the image build results into a debian package

    In step 3. the bootstrap root tarball was created but not yet packaged. A debian package is needed such that it can be referenced with the bootstrap_package attribute and the repository providing it. The simplest way to package the bootstrap-root tarball is to create another package in OBS and use the tarball file as its source.