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snapbtrex

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snapbtrex is a small utility that keeps snapshots of btrfs filesystems and optionally send them to a remote system or syncs them locally.

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# snapbtrex

snapbtrex is a small utility that keeps snapshots of btrfs filesystems and optionally send it to a remote system.

The script came originally from <https://btrfs.wiki.kernel.org/index.php/SnapBtr> . This is an extended version which is
capable of transferring snapshots to remote systems.

You can run it regularly (for example in a small script in cron.hourly or in crontab), or once in a while, to maintain
an "interesting" (see below) set of snapshots (backups). You may manually add or remove snapshots as you like,
use `snapbtrex.DATE_FORMAT` (in GMT) as snapshot-name.

It will keep at most `--target-backups` snapshots and ensure that
`--target-freespace` is available on the file-system by selecting snapshots to remove.

Using `--keep-backups`, you can ensure that at least some backups are kept, even if `--target-freespace` cannot be
satisfied.

snapbtrex will keep backups with exponentially increasing distance as you go back in time. It does this by selecting
snapshots to remove as follows.

The snapshots to remove is selected by "scoring" each space between snapshots, (newer, older). snapbtrex will remove the
older of the two snapshots in the space that have the lowest score.

The scoring mechanism integrates e^x from (now-newer) to (now-older)
so, new pairs will have high value, even if they are tightly packed, while older pairs will have high value if they are
far apart.

Alternatively you can also keep only the latest snapshots via `--keep-only-latest`
or set a maximum age for your snapshots with the `--max-age` parameter.

## Transferring Snapshots to Remote Host

snapbtrex uses the btrfs send and receive commands to transfer snapshots from a sending host to a receiving host via
ssh. Using `--ssh-port`, you can specify the port on which such ssh connections will be attempted.

Both hosts have to be prepared as in the setup instructions if you want to call the script via cronjob. You can always
call snapbtrex as standalone script if you have appropriate rights.

Specify your target host via  `--remote-host` and the directory with the `--remote-dir` options. Both options have to be
present. The target directory has to be located within a btrfs file system, and it has to be mounted via the root
volume, or else btrfs might fail to receive snapshots.

### Setup instructions

For transfer backups with ssh within an automated script (cronjob) you have to prepare the systems with the following
steps.

1\. create user `snapbtr` on both systems

```sh
sudo adduser snapbtr
```

2\. generate ssh key on the sender and copy public key to receiving machine

```sh
su - snapbtr
ssh-keygen
ssh-copy-id snapbtr@123.45.56.78
```

3\. create a sudoers include file at the receiving machine (use `sudo visudo`)

File: `/etc/sudoers.d/90_snapbtrrcv`

Minimum content is this for receiving snapshots on a remote system:

```sh
snapbtr ALL=(root:nobody) NOPASSWD:NOEXEC: /bin/btrfs receive*
```

If you want to link the latest transferred snapshot remotely with `--remote-link`
then you will need another line (adopt path to your specific path):

```sh
snapbtr ALL=(root:nobody) NOPASSWD:NOEXEC: /bin/ln -sfn /path/to/backups/* /path/to/current/current-link
```

If you want remote pruning of snapshots via `--remote-keep` option, then add this:

```sh
snapbtr ALL=(root:nobody) NOPASSWD:NOEXEC: /bin/btrfs subvolume delete*
```

4\. Create a sudoers include file on the sending machine

File: `/etc/sudoers.d/90_snapbtrsnd`

Contents:

```sh
snapbtr ALL=(root:nobody) NOPASSWD:NOEXEC: /bin/btrfs send*
snapbtr ALL=(root:nobody) NOPASSWD:NOEXEC: /bin/btrfs subvolume*
snapbtr ALL=(root:nobody) NOPASSWD:NOEXEC: /bin/btrfs filesystem sync*
```

Hint 1: For a more secure setup you should include the specific paths at the sudoers files.

Hint 2: On some Linux flavors you might find the btrfs tools in `/sbin/btrfs`
opposed to `/bin/btrfs`, the sudoers files have to reflect that. Try using
`which btrfs` to find out the full path to your `btrfs`.

## Examples

### Shell

Snapshot a volume and keep 20 versions:

```sh
sudo snapbtrex.py --snap /mnt/btrfs/@subvol1/ --path /mnt/btrfs/.mysnapshots/subvol1/ --target-backups 20
```

Snapshot a volume and copy the snapshot to different device

```sh
sudo snapbtrex.py --snap /mnt/btrfs/@subvol1/ --path /mnt/btrfs/.mysnapshots/subvol1/ --target-backups 20 --sync /mnt/btrfs_archive/backups
```

### Crontab

Snapshot and transfer to remote host every day at 4:10 am, keep 52 snapshots on the origin host (keeps all remote
backups, unless you delete them manually)

```sh
10 4    * * *   snapbtr /opt/snapbtrex/snapbtrex.py --snap /mnt/btrfs/@subvol1/ --path /mnt/btrfs/.mysnapshots/subvol1/ --target-backups 52 --verbose --remote-host 123.45.56.78 --remote-dir /mnt/btrfs/.backup/subvol1/  >> /var/log/snapbtrex.log
```

Snapshot and transfer to remote host every day at 4:20 am, keep 10 snapshots on the origin host and keep only 50
snapshots on the remote host.

```sh
20 4    * * *   snapbtr /opt/snapbtrex/snapbtrex.py --snap /mnt/btrfs/@subvol2/ --path /mnt/btrfs/.mysnapshots/subvol2/ --target-backups 10 --verbose --remote-host 123.45.56.78 --remote-dir /mnt/btrfs/.backup/subvol2/ --remote-keep 50 >> /var/log/snapbtrex.log
```

## Migrating from SnapBtr

If you created snapshots with [snapbtr](https://btrfs.wiki.kernel.org/index.php/SnapBtr)
then those snapshots were created as read/write snapshots. The sending of snapshots to remote hosts demands that those
snaps are read only. You can change rw snaps to ro snaps in the directory of the snapshots via:

```sh
sudo find . -maxdepth 1 -type d -exec btrfs property set -t s {} ro true \;
```

snapbtrex

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