99_bootprep is the Snapper rollback plugin for BootPrep.
Its responsibility is intentionally small: when Snapper performs a rollback, the plugin receives the resulting writable snapshot number and passes it to the BootPrep preparation engine.
Snapper rollback
|
v
99_bootprep
|
v
bootprep prepare <snapshot-number>
Snapper remains responsible for the rollback. BootPrep remains responsible for preparing the resulting writable snapshot for the next boot.
Snapper already knows how to create snapshots and perform rollbacks. BootPrep already knows how to prepare an already-selected writable snapshot and its boot environment.
The missing piece is the connection between them.
99_bootprep provides that connection without duplicating either tool's
responsibility. It allows a normal Snapper rollback to hand its result
directly to the same bootprep prepare engine used by other
BootPrep-aware workflows.
The plugin is installed at:
/usr/lib/snapper/plugins/99_bootprep
When Snapper invokes the plugin, 99_bootprep first examines the
operation supplied in its first argument.
Only the post-rollback operation:
rollback-post
are handled. All other Snapper operations exit successfully without invoking BootPrep.
For a rollback-post callback, the plugin verifies that:
/usr/sbin/bootprep
is installed and executable.
It then reads the resulting snapshot number from Snapper's fifth plugin argument:
SNAPSHOT="${5:-}"If no snapshot number is supplied, the plugin exits with an error rather than invoking BootPrep with incomplete data.
Once validated, the plugin hands control directly to the BootPrep engine:
exec /usr/sbin/bootprep prepare "$SNAPSHOT"The use of exec is intentional. The plugin does not remain as an
unnecessary intermediate process after its job is complete; BootPrep
replaces it and becomes responsible for the remainder of the preparation
transaction.
Version 2.1.0 wraps the complete callback and preparation transaction in
one bounded, root-only log beneath /var/lib/bootprep/logs. Nested
BootPrep execution shares that log instead of creating a second one.
The complete integration is:
User initiates a Snapper rollback
|
v
Snapper performs the rollback
|
v
Snapper creates/selects the writable rollback result
|
v
Snapper invokes 99_bootprep
|
v
99_bootprep recognizes the rollback callback
|
v
99_bootprep reads the resulting snapshot number
|
v
bootprep prepare <snapshot-number>
|
v
BootPrep prepares the next boot
The important distinction is that BootPrep receives the resulting writable snapshot number supplied by Snapper. The snapshot originally selected for rollback and the writable snapshot produced by that rollback are not necessarily the same snapshot.
The plugin does not attempt to infer this relationship. Snapper already knows the result of its own rollback operation, so the plugin simply passes that result to BootPrep.
The plugin follows BootPrep's single-responsibility design.
Snapper is responsible for:
- Snapshot management.
- Performing the rollback.
- Creating/selecting the writable rollback result.
- Setting the appropriate Btrfs default subvolume.
- Supplying the resulting snapshot number through the plugin callback.
99_bootprep is responsible for:
- Recognizing Snapper rollback callbacks.
- Ignoring unrelated Snapper operations.
- Verifying that BootPrep is available.
- Validating that a resulting snapshot number was supplied.
- Passing that snapshot number to
bootprep prepare.
BootPrep is responsible for:
- Preparing the already-selected writable snapshot and its boot environment.
- Performing the BootPrep preparation transaction.
- Leaving the selected snapshot ready for the next boot.
The plugin does not create snapshots, perform rollbacks, manage Btrfs subvolumes, regenerate GRUB itself, or reproduce any part of the BootPrep preparation engine.
99_bootprep deliberately performs only the validation required for its
own responsibility.
If the callback is not rollback-post, the plugin exits
successfully and does nothing.
If BootPrep is not installed or is not executable, the plugin reports:
snapper-bootprep: BootPrep not found: /usr/sbin/bootprep
If Snapper does not supply a resulting snapshot number, the plugin reports:
snapper-bootprep: No snapshot number supplied.
Otherwise, the plugin announces the snapshot being prepared and transfers control to BootPrep.
Any failure after that point belongs to the BootPrep preparation transaction and is reported by the BootPrep engine itself.
The log records combined output and the final exit status. BootPrep keeps the ten newest logs, limits each one to 1 MiB, and prevents another logged operation from running concurrently.
99_bootprep is installed automatically by bootprep-install.sh as
part of a normal BootPrep installation.
Installed location:
/usr/lib/snapper/plugins/99_bootprep
For an existing BootPrep installation, bootprep-upgrade.sh reinstalls
and verifies the Snapper plugin together with the BootPrep engine and
Btrfs orchestrator.
No separate plugin installation procedure is required.
BootPrep 2.x provides two distinct paths into the same preparation engine.
Snapper rollback:
snapper rollback
|
v
99_bootprep
|
v
bootprep prepare
Manual Btrfs activation:
bootprep-btrfs activate
|
v
Btrfs activation workflow
|
v
bootprep prepare
99_bootprep bridges Snapper's rollback workflow to BootPrep.
bootprep-btrfs orchestrates BootPrep-aware Btrfs workflows.
Both ultimately delegate final boot preparation to the same
bootprep prepare engine rather than duplicating its functionality.
99_bootprep is intentionally small.
It does not need to understand the BootPrep preparation transaction, discover the Btrfs layout, or reproduce Snapper's rollback logic. Snapper has already performed the rollback, and BootPrep already knows how to prepare its result.
The plugin only connects them.
Snapper performs the rollback. The plugin passes the result. BootPrep prepares the next boot.
That narrow boundary keeps the integration simple and allows the BootPrep engine, Snapper integration, and other BootPrep-aware workflows to evolve independently while continuing to share the same preparation interface.
Item Value
Component 99_bootprep
Type Snapper rollback plugin
Installed location /usr/lib/snapper/plugins/99_bootprep
Recognized operation rollback-post
Operation log /var/lib/bootprep/logs/bootprep-*.log
Snapshot argument Snapper plugin argument ${5}
BootPrep interface bootprep prepare <snapshot-number>
Non-rollback operations Ignored
Snapshot creation and rollback Snapper
Boot preparation BootPrep
README.md--- BootPrep overview, installation, and operation.ARCHITECTURE.md--- BootPrep architecture and separation of responsibilities.BOOTPREP_BTRFS.md--- Btrfs orchestrator documentation.CHANGELOG.md--- Release history.