36d0c5b9d1
- init.sh: creates the @ / @home / @log / @snapshots subvolume layout on a target device (the installer step). - snapshot.sh: scheduled read-only snapshots with pruning, installed as /usr/local/sbin/arcline-snapshot. - rollback.sh: safe boot-to-snapshot rollback that refuses to touch the live @ and promotes a snapshot atomically.
39 lines
1.7 KiB
Markdown
39 lines
1.7 KiB
Markdown
# btrfs in Arcline OS
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Arcline OS is **btrfs-native**: the root filesystem layout is created at
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install time and snapshots are first-class, not bolted on.
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## Subvolume layout
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| Subvolume | Mount point | Purpose |
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|--------------|---------------|------------------------------------------------|
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| `@` | `/` | system root — rolled back on failed upgrade |
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| `@home` | `/home` | user data — not rolled back by default |
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| `@log` | `/var/log` | logs survive rollbacks |
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| `@snapshots` | `/.snapshots` | read-only snapshots live here |
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The layout is created by `btrfs/init.sh <device>` (this is what the installer
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runs). `/etc/fstab` templates live in each edition manifest and reference these
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subvolumes with `subvol=` mount options.
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## Tooling
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- `btrfs/init.sh <device>` — create the subvolume layout on a target device.
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- `btrfs/snapshot.sh` — snapshot / list / prune. Installed in images as
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`/usr/local/sbin/arcline-snapshot` and triggered automatically by the
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`arcline-snapshot.timer` systemd unit (see `overlays/base/usr/lib/systemd/system/`).
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- `btrfs/rollback.sh` — promote a snapshot back to `@`. Installed as
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`/usr/local/sbin/arcline-rollback`.
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## How a rollback works
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Rollbacks are done from a rescue/live environment (never against the mounted
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`@`). The tool moves the current `@` aside to `@.rollback-<ts>` and promotes
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the chosen snapshot to `@`. Because btrfs renames are atomic, a crash mid-way
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leaves a recoverable system on disk.
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## Compression
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All subvolumes mount with `compress=zstd:3` (see the edition `fstab`
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templates). Transparent compression is on by default.
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