bootc-root-setup.service - Man Page

A oneshot systemd service that runs in the initramfs to set up the root filesystem when the composefs backend is active.  It is gated on the composefs= kernel command line argument and on ConditionPathExists=/etc/initrd-release, so it only runs inside an initramfs.

The service is ordered after sysroot.mount and before initrd-root-fs.target.  It performs the following steps:

1. Opens the composefs repository at /sysroot/composefs.
2. Mounts the EROFS image identified by the composefs=<digest> kernel argument, with fs-verity verification.
3. Optionally wraps the root in a transient tmpfs overlay (see root.transient in bootc-setup-root-conf.toml(5)).
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.

Behaviour is controlled by an optional TOML file installed into the initramfs:

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

See bootc-setup-root-conf.toml(5) for the full option reference.

The service and its binary (/usr/lib/bootc/initramfs-setup) are installed into the initramfs by the 51bootc dracut module.  The module also installs /usr/lib/composefs/setup-root-conf.toml when it is present on the host image, so image authors do not need manual dracut --include invocations.

The 51bootc module is not enabled by default (so that e.g. apt|dnf install bootc don't pull it in). It's recommended for base images to enable it via a config file in e.g. /usr/lib/dracut/dracut.conf.d.

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

v1.16.0

bootc-setup-root-conf(5).