BOOTC-ROOT-SETUP.SERVICE(5)

💖 bootc-root-setup.service 💖

okay bestie, so this is the manual page for bootc-root-setup.service — it lives in File Formats Manual (section 5, iykyk). it's a tiny little systemd service with main character energy and honestly? it's lowkey doing the most important job in the whole boot. let's get into it 🫶

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✨ NAME ✨

bootc-root-setup.service — that's her. that's the girl.

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🌸 DESCRIPTION 🌸

so like, this is a oneshot systemd service that runs in the initramfs, and its whole vibe is setting up the root filesystem whenever the composefs backend is active. it's gated on the composefs= kernel command line argument and on:

ConditionPathExists=/etc/initrd-release

...which means it only ever runs inside an initramfs. no initrd, no service, periodt. 💅

the service is ordered after sysroot.mount and before initrd-root-fs.target. and she performs these steps, in this exact order:

1. Opens the composefs repository at /sysroot/composefs.
2. Mounts the EROFS image identified by the composefs=<digest> kernel argument, with fs-verity verification. (yes, she verifies. she's careful. we love a secure queen. 🔥)
3. Optionally wraps the root in a transient tmpfs overlay — see root.transient in bootc-setup-root-conf.toml(5) for that one.
4. Bind-mounts or overlays /etc and /var from the per-deployment state directory at /sysroot/state/deploy/<digest>/.
5. Replaces /sysroot with the fully assembled root, ready for switch-root. slay, assembled, done. 💖

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🎀 CONFIGURATION 🎀

her behaviour is controlled by an optional TOML file that gets installed into the initramfs:

/usr/lib/composefs/setup-root-conf.toml

and if you wanna know every single lil option in there, go read bootc-setup-root-conf.toml(5). that's your full option reference, bestie. the whole menu. 🍓

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🦋 INSTALLATION 🦋

so the service itself, plus its binary at /usr/lib/bootc/initramfs-setup, get installed into the initramfs by the 51bootc dracut module. that module also installs:

/usr/lib/composefs/setup-root-conf.toml

...but only when it's present on the host image. which means image authors do not need to write out manual dracut --include invocations by hand. she does it for you. iconic behaviour, no notes. 👑

⚠️ okay important lil heads up: the 51bootc module is not enabled by default — this is on purpose, so that stuff like apt|dnf install bootc doesn't pull it in as a surprise. for base images though, it's recommended to enable it via a config file in e.g. /usr/lib/dracut/dracut.conf.d. do that. your future self will thank you. 🙈

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👀 SEE ALSO 👀

• bootc-setup-root-conf.toml(5)
• bootc(8)

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⭐ VERSION ⭐

v1.17.1

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and that's the whole page, bestie!! go forth and boot your composefs roots with confidence 💜🌈✨

stay hydrated, read your dracut configs, and remember: /etc/initrd-release is the vibe check this service never fails. 🧚💅

— mwah, from the File Formats Manual, BOOTC-ROOT-SETUP.SERVICE(5), version v1.17.1 🎀