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

sudo adduser snapbtr

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

su - snapbtr
ssh-keygen
ssh-copy-id [email protected]

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:

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):

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:

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:

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:

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

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)

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.

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 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:

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