Circumvent Debian Bootstrap

When building Debian-based images, KIWI NG uses apt in the bootstrap and the system phase to create the image root tree. However, apt does not support a native way to bootstrap an empty root tree. Therefore, the bootstrap phase uses apt only to resolve the given bootstrap packages and to download these packages from the given repositories. The list of packages is then manually extracted into the new root tree, which is not exactly the same as if apt would have installed them natively. For the purpose of creating an initial tree to begin with, this procedure is acceptable, though.

If, for some reason, this bootstrap procedure is not applicable, KIWI NG allows for an alternative process that 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"/>
</packages>

The bootstrap 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 is 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 than using KIWI NG’s Debian bootstrap method to do the job comes with the task of creating that package, providing the bootstrap root tree. There is 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.

Create an OBS project and repository setup that matches your image target.
Create an image build package.
```
osc mkpac bootstrap-root
```

Create the following appliance.kiwi file:

<image schemaversion="7.4" name="bootstrap-root">
    <description type="system">
        <author>The Author</author>
        <contact>author@example.com</contact>
        <specification>prebuilt bootstrap rootfs for ...</specification>
    </description>

    <preferences>
        <version>1.0.1</version>
        <packagemanager>apt</packagemanager>
        <type image="tbz"/>
    </preferences>

    <repository type="rpm-md">
        <source path="obsrepositories:/"/>
    </repository>

    <packages type="image">
        <package name="gawk"/>
        <package name="apt-utils"/>
        <package name="debconf"/>
        <package name="mawk"/>
        <package name="libpam-runtime"/>
        <package name="util-linux"/>
        <package name="systemd"/>
        <package name="init"/>
        <package name="gnupg"/>
        <package name="iproute2"/>
        <package name="iptables"/>
        <package name="iputils-ping"/>
        <package name="ifupdown"/>
        <package name="isc-dhcp-client"/>
        <package name="netbase"/>
        <package name="dbus"/>
        <package name="xz-utils"/>
        <package name="usrmerge"/>
        <package name="language-pack-en"/>
    </packages>

    <packages type="bootstrap"/>
</image>

osc add appliance.kiwi
osc ci

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 so 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.