AlmaLinux Atomic SIG modernizes build tooling with bootc-base-imagectl and image-builder

The AlmaLinux Atomic SIG has released version 13 of atomic-ci, its GitHub Actions-based build system for bootc images. The update replaces hhd-dev/rechunk with bootc-base-imagectl rechunk and switches ISO generation from bootc-image-builder to image-builder. Users gain live-boot ISOs that run without network access and new aarch64 installer images. Existing Atomic Desktop and Workstation users will download a full image on their first post-update pull due to layer reorganization, then resume delta updates.

What changed in atomic-ci v13

• Rechunking: Moved from hhd-dev/rechunk to bootc-base-imagectl rechunk, which is now the community-recommended approach and ships in the AlmaLinux bootc base image itself
• ISO generation: Replaced bootc-image-builder with image-builder; new ISOs boot into a live desktop session and include a partitioning tool, with offline installation possible since the image is on the media
• Architecture support: Added aarch64 ISOs alongside existing aarch64 images
• CI infrastructure: Builds now run on Ubuntu 26.04; branch builds are signed (PR builds remain unsigned until merge)
• Respin compatibility: v13 contains breaking changes for respin maintainers; iso.toml is removed, kickstart customizations move to hook-script, and some input names changed

Why it matters

The changes align AlmaLinux Atomic with current bootc community standards, reducing maintenance burden as tooling evolves. The live-boot ISOs lower the barrier to trying Atomic Desktop on real hardware before installation, and aarch64 ISO support expands platform coverage for ARM-based workstations and servers.