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Tool for creating snapshots and remote backups of btrfs subvolumes

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Btrbk is a backup tool for btrfs subvolumes, taking advantage of btrfs specific capabilities to create atomic snapshots and transfer them incrementally to your backup locations.

The source and target locations are specified in a config file, which allows to easily configure simple scenarios like "laptop with locally attached backup disks", as well as more complex ones, e.g. "server receiving backups from several hosts via ssh, with different retention policy".

Key Features:

  • Atomic snapshots
  • Incremental backups
  • Configurable retention policy
  • Backups to multiple destinations
  • Transfer via ssh
  • Resume of backups (if backup target was not reachable for a while)
  • Encrypted backups to non-btrfs destinations
  • Wildcard subvolumes (useful for docker and lxc containers)
  • Transaction log
  • Comprehensive list and statistics output
  • Resolve and trace btrfs parent-child and received-from relationships
  • Display file changes between two backups

Btrbk is designed to run as a cron job for triggering periodic snapshots and backups, as well as from the command line (e.g. for instantly creating additional snapshots).


Btrbk is a single perl script, and does not require any special installation procedures or libraries. Download the latest btrbk source tarball, or try latest master:

chmod +x btrbk
sudo ./btrbk ls /

For more information, read the installation documentation.


  • btrfs-progs: Btrfs filesystem utilities >= v4.12
  • Perl interpreter: Probably already installed on your system
  • OpenSSH: If you want to transfer backups from/to remote locations
  • mbuffer: If you want rate limiting and progress bars


Please consult the btrbk(1) man-page provided with this package for a full description of the command line options.

Configuration File

Before running

, you will need to create a configuration file. You might want to take a look at
provided with this package. For a detailed description, please consult the btrbk.conf(5) man-page.

When playing around with config-files, it is highly recommended to check the output using the

command before executing the backups:
btrbk -c /path/to/myconfig -v dryrun

This will read all btrfs information on the source/target filesystems and show what actions would be performed (without writing anything to the disks).

Example: laptop with usb-disk for backups

In this example, we assume you have a laptop with:

  • a disk having a btrfs root subvolume (subvolid=5) mounted on
    , containing a subvolume
    for the root filesystem (i.e. mounted on
    ) and a subvolume
    for the user data,
  • a directory or subvolume
    which will hold the btrbk snapshots,
  • a backup disk having a btrfs volume mounted as
    , containing a subvolume or directory
    for the incremental backups.

Retention policy:

  • keep all snapshots for 2 days, no matter how frequently you (or your cron-job) run btrbk
  • keep daily snapshots for 14 days (very handy if you are on the road and the backup disk is not attached)
  • keep monthly backups forever
  • keep weekly backups for 10 weeks
  • keep daily backups for 20 days


snapshot_preserve_min   2d
snapshot_preserve      14d

target_preserve_min no target_preserve 20d 10w *m

snapshot_dir btrbk_snapshots

volume /mnt/btr_pool target /mnt/btr_backup/mylaptop subvolume rootfs subvolume home [...]


exec /usr/bin/btrbk -q -c /etc/btrbk/btrbk-mylaptop.conf run
  • This will create snapshots on a daily basis:
    • /mnt/btr_pool/btrbk_snapshots/rootfs.YYYYMMDD
    • /mnt/btr_pool/btrbk_snapshots/home.YYYYMMDD
  • And create incremental backups in:
    • /mnt/btr_backup/mylaptop/rootfs.YYYYMMDD
    • /mnt/btr_backup/mylaptop/home.YYYYMMDD

If you want the snapshots to be created only if the backup disk is attached, simply add the following line to the config:

snapshot_create ondemand

For a quick additional snapshot of your home, run:

# btrbk snapshot home

Example: host-initiated backup on fileserver

Let's say you have a fileserver at "" where you want to create backups of your laptop disk, the config would look like this:

ssh_identity /etc/btrbk/ssh/id_rsa

volume /mnt/btr_pool subvolume rootfs target /mnt/btr_backup/mylaptop target ssh://

In addition to the backups on your local usb-disk mounted at

, incremental backups would also be pushed to

Example: fileserver-initiated backups from several hosts

If you're a sysadmin and want to trigger backups directly from your fileserver, the config would be something like:

ssh_identity /etc/btrbk/ssh/id_rsa

volume ssh:// target /mnt/btr_backup/alpha subvolume rootfs subvolume home

volume ssh:// target /mnt/btr_backup/beta subvolume rootfs subvolume dbdata

This will pull backups from alpha/ and locally create:

  • /mnt/btr_backup/alpha/rootfs.YYYYMMDD
  • /mnt/btr_backup/alpha/home.YYYYMMDD
  • /mnt/btr_backup/beta/rootfs.YYYYMMDD
  • /mnt/btr_backup/beta/dbdata.YYYYMMDD

Example: local time-machine (hourly snapshots)

If all you want is to create snapshots of your home directory on a regular basis:


timestamp_format        long
snapshot_preserve_min   18h
snapshot_preserve       48h 20d 6m

volume /mnt/btr_pool snapshot_dir btrbk_snapshots subvolume home


exec /usr/bin/btrbk -q run

Note that you can run btrbk more than once an hour, e.g. by calling

sudo btrbk run
from the command line. With this setup, all those extra snapshots will be kept for 18 hours.

Example: multiple btrbk instances

Let's say we have a host (at running btrbk with the setup of the time-machine example above, and we need a backup server to only fetch the snapshots.

/etc/btrbk/btrbk.conf (on backup server):

target_preserve_min        no
target_preserve            0d 10w *m

volume ssh:// target /mnt/btr_backup/my-laptop subvolume home snapshot_dir btrbk_snapshots snapshot_preserve_min all snapshot_create no

If the server runs btrbk with this config, 10 weeklies and all monthlies are received from The source filesystem is never altered because of

snapshot_preserve_min all

Example: virtual machine setup

Common virtual machine setups have multiple volume sections with same host, but distinct port numbers for each machine.


# This propagates to all subvolume sections:
target /mnt/btr_backup/

volume ssh://localhost:2201/mnt/btr_pool group vm vm01 subvolume home snapshot_name vm01-home subvolume data snapshot_name vm01-data

volume ssh://localhost:2202/mnt/btr_pool group vm vm02 subvolume home snapshot_name vm02-home

volume ssh://localhost:2203/mnt/btr_pool [...]

This will create

, ...

Note that btrbk holds a single reference to every btrfs filesystem tree, regarding UUID's as "globally unique". If the configured subvolumes point to the same filesystem on different machines (ports), you will see log lines like this when running

btrbk -v
Assuming same filesystem: "ssh://localhost:2201/dev/sda1", "ssh://localhost:2202/dev/sda1"

Example: backup from non-btrfs source

If you want to make backups from a filesystem other than btrfs (e.g. ext4 or reiserfs), you need to create a synchronization subvolume on the backup disk:

# btrfs subvolume create /mnt/btr_backup/myhost_sync

Configure btrbk to use

as source subvolume:
volume /mnt/btr_backup
  subvolume myhost_sync
    snapshot_name           myhost

snapshot_preserve_min   latest
snapshot_preserve       14d 20w *m

The btrbk package provides the "btrbk-mail" script, which automates the synchronization using rsync, and can be run as cron job or systemd timer unit. For configuration details, see the config section in "/contrib/cron/btrbk-mail".

Alternatively, you can run any synchronization software prior to running btrbk. Something like:

rsync -az --delete \
      --inplace --numeric-ids --acls --xattrs \
      -e 'ssh -i /etc/btrbk/ssh/id_rsa' \ \

exec /usr/bin/btrbk -q run

This will produce snapshots

, with retention as defined with the snapshot_preserve option.

Example: encrypted backup to non-btrfs target

If your backup server does not support btrfs, you can send your subvolumes to a raw file.

This is an experimental feature: btrbk supports "raw" targets, meaning that similar to the "send-receive" target the btrfs subvolume is being sent using

btrfs send
(mirroring filesystem level data), but instead of instantly being received (
btrfs receive
) by the target filesystem, it is being redirected to a file, optionally compressed and piped through GnuPG.


raw_target_compress   xz
raw_target_encrypt    gpg
gpg_keyring           /etc/btrbk/gpg/pubring.gpg
gpg_recipient         [email protected]

volume /mnt/btr_pool subvolume home target raw ssh:// ssh_user btrbk # incremental no

This will create a GnuPG encrypted, compressed files on the target host. For each backup, two files are created:

  • /backup/home.YYYYMMDD.btrfs.xz.gpg
    : main data file containing the btrfs send-stream,
  • /backup/
    : sidecar file containing metadata used by btrbk.

I you are using raw incremental backups, please make sure you understand the implications (see btrbk.conf(5), TARGET TYPES).

Setting up SSH

Since btrbk needs root access, it is very advisable to take all the security precautions you can. In most cases backups are generated periodically without user interaction, so it is not possible to protect your ssh key with a password. The steps below will give you hints on how to secure your ssh server for a backup scenario. Note that the

executable is not needed on the remote side, but you will need the
executable from the btrfs-progs package.

Step 1: Create SSH keypair

On the client side, create a ssh key dedicated to btrbk, without password protection:

ssh-keygen -t rsa -b 2048 -f /etc/btrbk/ssh/id_rsa -C [email protected] -N ""

The content of the public key (/etc/btrbk/ssh/ is used for authentication in "authorizedkeys" on the server side (see sshd(8) for details).

Step 2 (option): root login restricted by ""

Btrbk comes with a shell script "", which restricts ssh access to sane calls to the "btrfs" command needed for snapshot creation and send/receive operations (see sshfilterbtrbk(1)).

Copy "" to "/backup/scripts/", and configure sshd to run it whenever the key is used for authentication. Example "/root/.ssh/authorized_keys":

# example backup source (also allowing deletion of old snapshots)
command="/backup/scripts/ -l --source --delete" ...

example backup target (also allowing deletion of old snapshots)

command="/backup/scripts/ -l --target --delete" ...

example fetch-only backup source (snapshot_preserve_min=all, snapshot_create=no),

restricted to subvolumes within /home or /data

command="/backup/scripts/ -l --send -p /home -p /data" ...

Step 2 (option): dedicated user login, using different backend

Create a user dedicated to btrbk and add the public key to "/home/btrbk/.ssh/authorized_keys". In "btrbk.conf", choose either:

  • backend btrfs-progs-btrbk
    to use separated binaries with elevated privileges (suid or fscaps) instead of the "btrfs" command (see btrfs-progs-btrbk).
  • backend btrfs-progs-sudo
    , configure "/etc/sudoers" and add the --sudo

Further considerations

You might also want to restrict ssh access to a static IP address within your network:

from="",command=... ...

For even more security, set up a chroot environment in "/etc/ssh/sshdconfig" (see [sshdconfig(5)]).

Restoring Backups

Btrbk does not provide any mechanism to restore your backups, this has to be done manually. In the instructions below, we assume that you have a btrfs volume mounted at

, and the subvolume you want to restore is at

Important: don't use

btrfs property set
to make a subvolume read-write after restoring. This is a low-level command, and leaves "Received UUID" in a false state which causes btrbk to fail on subsequent incremental backups. Instead, use
btrfs subvolume
flag) as described below.

Step 0: Identify Subvolume

# list snapshots managed by btrbk
btrbk list snapshots

alternative: list all subvolumes

btrbk ls / btrbk ls -L /

From the list, identify the snapshot you want to restore. Let's say it's


Step 1: Restore Backup

(skip this step if you restore from a snapshot)

# locally mounted backup disk
btrfs send /mnt/btr_backup/data.20150101 | btrfs receive /mnt/btr_pool/

from / to remote host

ssh [email protected] btrfs send /mnt/btr_backup/data.20150101 | btrfs receive /mnt/btr_pool/ btrfs send /mnt/btr_backup/data.20150101 | ssh [email protected] btrfs receive /mnt/btr_pool/

Hint: Try to send-receive backups incrementally if possible. In case you still have common snapshot / backup pairs (i.e. both "snapshotsubvol" and "targetsubvol" are listed above), use

send -p 

From this point on,

on both disks can be used as parents for subsequent send-receive operations, and a received_uuid relationship is established (see below).

Step 2: Create read-write Subvolume

# if still present, move broken subvolume away
mv /mnt/btr_pool/data /mnt/btr_pool/data.BROKEN

create read-write subvolume

btrfs subvolume snapshot /mnt/btr_pool/data.20150101 /mnt/btr_pool/data


subvolume is restored, you can carry on with incremental backups to

Step 3: Cleanup

# if everything went fine, delete the broken subvolume
btrfs subvolume delete /mnt/btr_pool/data.BROKEN

Make sure to keep

subvolumes on both disks at least until you created a new backup using btrbk, in order to keep the incremental chain alive.

Btrfs Relationship (technical note)

btrbk origin -t /mnt/btr_backup/data.20150101
btrbk ls -L /mnt/btr_pool /mnt/btr_backup
  • received_uuid relationship: correlated, identical read-only subvolumes, cross-filesystem.

    a.received_uuid = b.received_uuid
    a.received_uuid = b.uuid
    • Required for subvolumes used as parent (or clone-src) of send-receive operations.
    • Present on subvolumes created by
      btrfs send | btrfs receive
    • /mnt/btr_pool/data.20150101 === /mnt/btr_backup/data.20150101
  • parent_uuid relationship: "is-snapshot-of"

    a.parent_uuid = b.uuid
    • Present on subvolumes created by
      btrfs subvolume snapshot
      btrfs send -p | btrfs receive
    • Used by btrbk to determine best parent.
    • /mnt/btr_pool/data.20150101 


Make sure to also read the btrbk FAQ page. Help improve it by asking!


So btrbk saved your day?

I will definitively continue developing btrbk for free, but if you want to support me you can do so:



Source Code Repository

The source code for btrbk is managed using Git.

Official repository:

git clone

Mirror on GitHub:

git clone

How to Contribute

Your contributions are welcome!

If you would like to contribute or have found bugs:

Any feedback is appreciated!


btrbk is free software, available under the GNU General Public License, Version 3 or later.

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