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README.backup.md

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+# PBS Backup helper
+
+Client-side encrypted backups of a host to a Proxmox Backup Server (PBS)
+that is **outside our control**.
+
+Everything lives in `/opt/backup/`. The connection details and credentials
+(server, datastore, namespace, API token, encryption key) are kept in
+`backup.env` (git-ignored); see `backup.env.sample` for the format.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `backup.env` | Shared config: server, datastore, namespace, token, key (sourced by both scripts) |
+| `backup.env.sample` | Template — copy to `backup.env` and fill in real values |
+| `backup.sh` | Full backup of `/` with client-side encryption |
+| `restore.sh` | FUSE-mount the encrypted backup to browse/restore files |
+| `/etc/proxmox-backup/encryption-key.pem` | Client-side encryption key (store a copy off-host!) |
+| `/etc/proxmox-backup/defaults.exclude` | Paths excluded from the backup |
+
+## How `backup.sh` works
+
+1. Sources `backup.env`, which exports the connection/auth settings (server,
+   datastore, port, API token) as separate `PBS_*` component variables. This
+   matters: `PBS_AUTH_ID` is only honoured when `PBS_REPOSITORY` is *not* set.
+2. Builds `--exclude` flags from `/etc/proxmox-backup/defaults.exclude`
+   (`/proc`, `/sys`, `/dev`, `/run`, `/tmp`, …).
+3. Runs:
+
+   ```
+   proxmox-backup-client backup "${HOSTNAME}-root.pxar:/" \
+       --keyfile /etc/proxmox-backup/encryption-key.pem \
+       --ns "$BACKUP_NS" \
+       --exclude /proc/* ...
+   ```
+
+4. The client encrypts everything locally before uploading. The PBS only ever
+   stores ciphertext and cannot read the data.
+
+Encryption is client-side. The key file has no password (`kdf: none`), so
+**possession of the key file alone is enough to decrypt** — protect it.
+
+## What to store elsewhere (critical)
+
+The **encryption key is the only thing that makes the backups readable**. If
+this host and the key are both lost, the backup is unrecoverable — no one at
+the PBS provider can help.
+
+- File: `/etc/proxmox-backup/encryption-key.pem`
+- Fingerprint: `proxmox-backup-client key show /etc/proxmox-backup/encryption-key.pem`
+
+Keep a copy somewhere safe that is **not this machine**:
+- offline USB stick / printed paperkey
+- password manager
+- another trusted host
+
+Also record (or be able to re-issue) the API token secret, so you can reach the
+datastore at all. Losing the token costs you access; losing the key costs you
+the data.
+
+## How to restore files
+
+`restore.sh` has three modes. Pick based on how much you need back.
+
+Unless you pass a snapshot explicitly, each mode first lists the available
+snapshots and prompts you to pick one (default: the most recent). You can skip
+the prompt with `--snapshot <ref>` (or the positional snapshot on `mount`).
+
+For a few files, the FUSE mount is the fastest option (random access, only
+reads the path you touch). `restore --pattern` is the slowest (streams the
+whole archive); `shell` + `restore-selected` sits in between.
+
+### FUSE mount — browse, or restore a few files
+
+```
+./restore.sh                                  # mount latest snapshot at /mnt/pbs-restore
+./restore.sh /mnt/restore <snapshot>          # mount a specific snapshot
+```
+
+Then browse `/mnt/pbs-restore` and copy out what you need. Unmount with:
+
+```
+umount /mnt/pbs-restore
+```
+
+The mount does random access, so it only downloads the chunks for the files
+you actually read. That's cheap for a handful of files, but slow to walk a
+large tree (each file is a round-trip).
+
+### Bulk restore — a whole directory or many files
+
+```
+./restore.sh restore /restore/var/vmail "var/vmail/example.com/*"
+```
+
+Streams the archive sequentially and extracts the matching paths — the fast
+way to get a large directory or many files back. Patterns are globs against
+paths inside the archive and may be repeated; with none, the whole archive is
+extracted:
+
+```
+./restore.sh restore /mnt/full-restore
+```
+
+Note: pattern restore always reads the whole archive (it streams and filters),
+so it's wasteful for one or two files — use the mount for those.
+
+### Interactive shell — browse and selectively restore
+
+```
+./restore.sh shell
+```
+
+Drops into an interactive shell that navigates the backup via the catalog
+metadata, so browsing is fast (it doesn't read the archive). Useful commands:
+
+```
+ls [path]            list the current directory
+cd [path]            change directory
+pwd                  print current directory
+find <pattern>       search entries
+select <path>        mark an entry for restore
+deselect <path>      unmark an entry
+list-selected        show what is marked
+restore-selected <target>   restore everything marked
+exit                 quit
+```
+
+Note: `restore-selected` is catalog-driven — it reads only matched files'
+data, not the whole archive — but it still walks the entire catalog and fetches
+per-directory pxar metadata from the archive, so it's ~a minute on a large
+tree, not instant. For one or two files, `mount` + `cp` is much faster.
+
+### Manual `restore` (advanced)
+
+First source the shared config (`source /opt/backup/backup.env`), then:
+
+```
+proxmox-backup-client restore host/<hostname>/<time> <hostname>-root.pxar /restore/dir \
+    --ns <namespace> \
+    --keyfile /etc/proxmox-backup/encryption-key.pem \
+    --pattern "etc/postfix/main.cf"
+```
+
+## Snapshots
+
+The snapshot reference has the form `<type>/<id>/<UTC-time>`, e.g.
+`host/<hostname>/2026-09-19T10:36:14Z`. List available snapshots with:
+
+```
+proxmox-backup-client snapshot list host/<hostname> --ns <namespace>
+```