container export

Experimental features are subject to change or removal. Please do provide feedback on them.

Overview

The bootc container export command exports a container filesystem as a tar archive suitable for unpacking onto a target system.

However, this is a bit more than a simple format transformation:

The output includes SELinux labeling (computed from the image's policy)
The kernel can optionally be copied to /boot for compatibility with Anaconda's liveimg command

Usage

bootc container export [OPTIONS] TARGET

Options

--format <FORMAT> - Export format (default: tar)
-o, --output <PATH> - Output file (defaults to stdout)
--kernel-in-boot - Copy kernel and initramfs from /usr/lib/modules to /boot for legacy compatibility
--disable-selinux - Disable SELinux labeling in the exported archive

Examples

Complete example using podman

podman run --rm \
    --mount=type=image,source=quay.io/example/example,target=/run/target \
    quay.io/example/example \
    bootc container export --kernel-in-boot /run/target > example.tar

There is also an -o option to write to a file directly, but when using podman run shell redirection is simpler since -o would require a bind mount to write to the host filesystem.

Anaconda liveimg integration

A key targeted use case for this is Anaconda's liveimg kickstart command which accepts any generic filesystem payload (tar, squashfs).

The installed system will not have any bootc/ostree/composefs filesystem structure, will not be read-only etc. The semantics of the installed system are exactly the same as any other usage of Anaconda liveimg or equivalent.

Container image requirements

At the current time this is only tested with a workflow starting FROM quay.io/fedora/fedora-bootc or equivalent. In theory, this workflow would be compatible with an image starting with just FROM fedora then RUN dnf -y install kernel etc., but that is not tested.

For the first case right now, you must include as part of your container build this logic or equivalent:

RUN sed -i '/layout=ostree/d' /usr/lib/kernel/install.conf && \
    rm -vf /usr/lib/kernel/install.conf.d/*-bootc-*.conf \
           /usr/lib/kernel/install.d/*-rpmostree.install

The sed command removes the layout=ostree line from install.conf while preserving any other settings. The rm commands remove the bootc drop-in and rpm-ostree plugin that would otherwise intercept kernel-install and delegate to rpm-ostree (which doesn't work outside an ostree deployment).

Required kickstart configuration

While the liveimg verb handles most of the basics, some %post scripting is also required.

Bootloader setup via kernel-install

The %post script should use kernel-install add to set up the bootloader. This creates BLS entries, copies the kernel, and generates an initramfs via the standard plugin chain (50-dracut, 90-loaderentry, etc.):

%post --erroronfail
set -eux

KVER=$(ls /usr/lib/modules | head -1)

# Ensure machine-id exists (needed by kernel-install for BLS filenames)
if [ ! -s /etc/machine-id ]; then
    systemd-machine-id-setup
fi

# kernel-install creates the BLS entry, copies vmlinuz, and generates
# initramfs via the standard plugin chain (50-dracut, 90-loaderentry, etc.)
kernel-install add "$KVER" "/usr/lib/modules/$KVER/vmlinuz"

# Regenerate grub config to pick up BLS entries
grub2-mkconfig -o /boot/grub2/grub.cfg
%end

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