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sysext: Add fast path dev flow
For most work on `bootc upgrade` or `bootc switch`, rebuilding the full container image is unnecessary. This adds a fast-path workflow that builds just the bootc binary into a systemd-sysext and overlays it onto /usr in a persistent bcvk VM via virtiofs. For more info see the updated Justfile. There's still some TODOs here - e.g. we need to support running the TMT tests this way, etc. Assisted-by: OpenCode (claude-opus-4-6) Signed-off-by: Colin Walters <walters@verbum.org>
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‎CONTRIBUTING.md‎

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@@ -104,6 +104,31 @@ For the local case, check out [cstor-dist](https://github.com/cgwalters/cstor-di
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Another alternative is mounting via virtiofs (see e.g. [this PR to bcvk](https://github.com/bootc-dev/bcvk/pull/16)).
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If you're using libvirt, see [this document](https://libvirt.org/kbase/virtiofs.html).
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#### Using sysext for fast iteration
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For the fastest development cycle when working on the bootc client
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(e.g. `bootc upgrade`, `bootc switch`), you can use the sysext-based
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workflow. This builds the bootc binary via a container, shares it into
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a persistent VM via virtiofs, and overlays it onto `/usr` using
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systemd-sysext (~30s rebuild cycle):
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```bash
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# Build sysext and launch a persistent dev VM
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just bcvk up
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# After editing code, rebuild and refresh the overlay (~30s)
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just bcvk sync
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# SSH into the VM — bootc is your dev build
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just bcvk ssh bootc status
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# When done
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just bcvk down
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```
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The sysext overlay means `bootc` on the VM's PATH is your dev build.
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Run `just bcvk` to list all available commands.
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#### Running bootc against a live environment
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If your development environment host is also a bootc system (e.g. a

‎Dockerfile‎

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@@ -99,6 +99,23 @@ ENV SOURCE_DATE_EPOCH=${SOURCE_DATE_EPOCH}
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# Build RPM directly from source, using cached target directory
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RUN --network=none --mount=type=tmpfs,target=/run --mount=type=tmpfs,target=/tmp --mount=type=cache,target=/src/target --mount=type=cache,target=/var/roothome RPM_VERSION="${pkgversion}" /src/contrib/packaging/build-rpm
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# Build a systemd-sysext containing just the bootc binary.
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# Skips RPM machinery entirely for fast incremental rebuilds.
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FROM buildroot as sysext
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RUN --network=none --mount=type=tmpfs,target=/run --mount=type=tmpfs,target=/tmp \
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--mount=type=cache,target=/src/target --mount=type=cache,target=/var/roothome <<EORUN
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set -xeuo pipefail
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cargo build --bin bootc
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mkdir -p /out/bootc/usr/bin /out/bootc/usr/lib/extension-release.d
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cp target/debug/bootc /out/bootc/usr/bin/
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cat > /out/bootc/usr/lib/extension-release.d/extension-release.bootc <<EOF
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ID=_any
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EXTENSION_RELOAD_MANAGER=1
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EOF
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echo "Fast sysext created (binary only):"
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find /out/bootc -type f
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EORUN
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# This image signs systemd-boot using our key, and writes the resulting binary into /out
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FROM tools as sdboot-signed
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# The secureboot key and cert are passed via Justfile

‎Justfile‎

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# -> cargo xtask
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# --------------------------------------------------------------------
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mod bcvk 'bcvk.just'
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# Configuration variables (override via environment or command line)
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# Example: BOOTC_base=quay.io/fedora/fedora-bootc:42 just build
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eval $(just _git-build-vars)
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podman build {{base_buildargs}} --build-arg=SOURCE_DATE_EPOCH=${SOURCE_DATE_EPOCH} --build-arg=pkgversion=${VERSION} --target units -t localhost/bootc-units .
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# ============================================================================
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# Development VM workflow (sysext-based)
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# ============================================================================
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# Build a systemd-sysext via the container build (binary only, for fast iteration)
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[group('dev')]
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sysext:
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contrib/packaging/build-container-stage sysext target/sysext \
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{{base_buildargs}} $(just _local-deps-args)
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# ============================================================================
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# Internal helpers (prefixed with _)
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# ============================================================================
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echo "SOURCE_DATE_EPOCH=${SOURCE_DATE_EPOCH}"
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echo "VERSION=${VERSION}"
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_local-deps-args:
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#!/bin/bash
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set -euo pipefail
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if [[ -z "{{no_auto_local_deps}}" ]]; then
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cargo xtask local-rust-deps
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fi
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_keygen:
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./hack/generate-secureboot-keys
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‎bcvk.just‎

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# bcvk development VM management
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#
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# The dev binary is overlaid onto /usr via systemd-sysext. After
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# rebuilding with `just sysext`, run `just bcvk sync` to
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# refresh the overlay (~30s total cycle).
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#
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# Usage:
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# just bcvk up # Build sysext + launch persistent VM
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# just bcvk sync # Rebuild sysext + refresh overlay (~30s)
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# just bcvk ssh # SSH into the VM
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# just bcvk ephemeral # Ephemeral VM (full image, destroyed on exit)
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base_img := env("BOOTC_base_img", "localhost/bootc")
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# List available recipes
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[private]
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default:
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@just --list bcvk
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# Run an ephemeral VM from the latest build and SSH in (destroyed on exit)
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[group('ephemeral')]
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ephemeral:
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just build
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bcvk ephemeral run-ssh {{base_img}}
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# Launch persistent development VM with sysext
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[group('vm')]
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up:
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just sysext
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cargo xtask bcvk vm
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# Rebuild sysext and verify the new binary in the running VM
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[group('vm')]
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sync:
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just sysext
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cargo xtask bcvk sync
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# SSH into development VM (interactive shell if no args given)
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[group('vm')]
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ssh *ARGS:
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cargo xtask bcvk ssh {{ARGS}}
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# Stop and remove development VM
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[group('vm')]
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down:
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cargo xtask bcvk down
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# Show development VM status
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[group('vm')]
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status:
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cargo xtask bcvk status
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# Watch development VM logs
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[group('vm')]
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logs:
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cargo xtask bcvk logs
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# Show sysext status in development VM
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[group('vm')]
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sysext-status:
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cargo xtask bcvk ssh systemd-sysext status
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# Restart development VM
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[group('vm')]
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restart:
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#!/bin/bash
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set -euo pipefail
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echo "Restarting development VM..."
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cargo xtask bcvk ssh -- sudo systemctl reboot || true
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sleep 5
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echo "Waiting for VM to come back up..."
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for i in {1..30}; do
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if cargo xtask bcvk ssh -- echo "VM is up" 2>/dev/null; then
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echo "VM is back online!"
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break
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fi
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echo "Waiting... (attempt $i/30)"
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sleep 2
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done
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# Clean up all development resources (VM + sysext)
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[group('vm')]
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clean:
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cargo xtask bcvk clean

‎contrib/packaging/build-container-stage‎

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#!/bin/bash
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# Build a Dockerfile stage and extract /out to a versioned subdirectory.
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# Usage: build-container-stage <stage> <output-dir> [podman-build-args...]
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#
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# Each build creates a new timestamped directory inside <output-dir>
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# (e.g. output-dir/bootc-1234567890/) and prints the version name to
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# stdout on the last line. A "current" symlink is updated to point at
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# the new version. Old versions are pruned (keeping the 2 most recent)
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# so the previous version remains valid for any active overlay.
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set -euo pipefail
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stage="${1:?Usage: build-container-stage <stage> <output-dir> [podman-build-args...]}"
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output_dir="${2:?Usage: build-container-stage <stage> <output-dir> [podman-build-args...]}"
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shift 2
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image_tag="localhost/bootc-${stage}"
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podman build -t "${image_tag}" --target="${stage}" "$@" .
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mkdir -p "${output_dir}"
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# Extract into a versioned subdirectory, using the image build timestamp
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# so the version name reflects when the binary was actually built.
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version="bootc-$(podman inspect --format '{{.Created.Unix}}' "${image_tag}")"
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version_dir="${output_dir}/${version}"
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mkdir -p "${version_dir}"
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podman run --rm "${image_tag}" tar -C /out -cf - . | tar -C "${version_dir}" -xvf -
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chmod -R a+rX "${version_dir}"
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# Update the "current" symlink atomically
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ln -sfn "${version}" "${output_dir}/current.tmp"
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mv -Tf "${output_dir}/current.tmp" "${output_dir}/current"
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# Prune old versions, keeping the 2 most recent
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ls -1dt "${output_dir}"/bootc-[0-9]* 2>/dev/null | tail -n +3 | while read -r old; do
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rm -rf "${old}"
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done
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# Print the version name so callers (xtask) can use it
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echo "sysext-version=${version}"

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