Introduction

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
• Transaction log
• Display file changes between two backups

btrbk is intended to be run as a cron job.

Installation

btrbk comes as a single executable file (perl script), without the need of any installation procedures. If you want the package and man-pages properly installed, follow the instructions below.

Prerequisites

• btrfs-progs: Btrfs filesystem utilities (use "btrfs_progs_compat" option for hosts running version prior to v3.17)
• Perl interpreter: probably already installed on your system
• Date::Calc: Perl module

Instructions

In order to install the btrbk executable along with the man-pages and an example configuration file, choose one of the following methods:

Generic Linux System

Download and unpack the newest stable btrbk source tarball and type:

sudo make install

Gentoo Linux

Grab the digint portage overlay from: git://dev.tty0.ch/portage/digint-overlay.git

emerge app-backup/btrbk

Debian Based Distros

btrbk is in stretch (testing) (utils): https://packages.debian.org/stretch/btrbk

Packages are also available via NeuroDebian: http://neuro.debian.net/pkgs/btrbk.html

Arch Linux

btrbk is in AUR: https://aur.archlinux.org/packages/btrbk/

Alpine Linux

btrbk is in testing, install with:

apk add btrbk

Synopsis

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

Configuration File

Before running btrbk, you will need to create a configuration file. You might want to take a look at btrbk.conf.example 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 dryrun command before executing the backups:

btrbk -c 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 volume mounted as /mnt/btr_pool, containing a subvolume rootfs for the root filesystem and a subvolume home for the user data.
• a backup disk having a btrfs volume mounted as /mnt/btr_backup, containing a subvolume mylaptop for the incremental backups.

Retention policy:

• keep 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

/etc/btrbk/btrbk-mylaptop.conf:

snapshot_preserve_daily    14
snapshot_preserve_weekly   0
snapshot_preserve_monthly  0

target_preserve_daily      20
target_preserve_weekly     10
target_preserve_monthly    all

snapshot_dir               btrbk_snapshots

volume /mnt/btr_pool
  subvolume rootfs
    target send-receive    /mnt/btr_backup/mylaptop

  subvolume home
    target send-receive    /mnt/btr_backup/mylaptop

/etc/cron.daily/btrbk:

#!/bin/sh
exec /usr/sbin/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

Example: host-initiated backup on fileserver

Let's say you have a fileserver at "myserver.mydomain.com" 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 send-receive    /mnt/btr_backup/mylaptop
    target send-receive    ssh://myserver.mydomain.com/mnt/btr_backup/mylaptop

In addition to the backups on your local usb-disk mounted at /mnt/btr_backup/mylaptop, incremental backups would also be pushed to myserver.mydomain.com.

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://alpha.mydomain.com/mnt/btr_pool
  subvolume rootfs
    target send-receive    /mnt/btr_backup/alpha

  subvolume home
    target send-receive    /mnt/btr_backup/alpha

volume ssh://beta.mydomain.com/mnt/btr_pool
  subvolume rootfs
    target send-receive    /mnt/btr_backup/beta

  subvolume dbdata
    target send-receive    /mnt/btr_backup/beta

This will pull backups from alpha/beta.mydomain.com 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 (daily snapshots)

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

/etc/btrbk/btrbk.conf:

volume /mnt/btr_pool
  snapshot_dir btrbk_snapshots
  subvolume home

/etc/cron.daily/btrbk:

#!/bin/sh
exec /usr/sbin/btrbk -q run

Note that you can run btrbk more than once a day, e.g. by creating the above script in /etc/cron.hourly/btrbk, or by calling sudo btrbk run from the command line.

Example: multiple btrbk instances

Let's say we have a host (at 192.168.0.42) 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):

volume ssh://192.168.0.42/mnt/btr_pool
  subvolume home
    snapshot_dir             btrbk_snapshots
    snapshot_preserve_daily  all
    snapshot_create          no
    resume_missing           yes

    target_preserve_daily    0
    target_preserve_weekly   10
    target_preserve_monthly  all

    target send-receive  /mnt/btr_backup/my-laptop.com

If the server runs btrbk with this config, the latest snapshot (which is always transferred), 10 weeklies and all monthlies are received from 192.168.0.42. The source filesystem is never altered because of snapshot_preserve_daily all.

Example: backup from non-btrfs source

First create a btrfs subvolume on the backup server:

# btrfs subvolume create /mnt/btr_backup/myhost_sync

In your daily cron script, prior to running btrbk, sync your source to myhost_sync, something like:

rsync -a --delete -e ssh myhost.mydomain.com://data/ /mnt/btr_backup/myhost_sync/

Then run btrbk, with myhost_sync configured without any targets as follows:

volume /mnt/btr_backup
  subvolume myhost_sync
    snapshot_name    myhost

    snapshot_preserve_daily    14
    snapshot_preserve_weekly   20
    snapshot_preserve_monthly  all

This will produce daily snapshots /mnt/btr_backup/myhost.20150101, with retention as defined with the snapshot_preserve_* options.

Note that the provided script: "contrib/cron/btrbk-mail" has support for this!

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.

/etc/btrbk/btrbk.conf:

raw_target_compress  xz
raw_target_encrypt   gpg
gpg_keyring          /etc/btrbk/gpg/pubring.gpg
gpg_recipient        btrbk@mydomain.com

volume /mnt/btr_pool
  subvolume home
    target raw ssh://cloud.example.com/backup
      ssh_user     btrbk
      # incremental  no

This will create a GnuPG encrypted, compressed files on the target host:

• /backup/home.YYYYMMDD.btrfs_<received_uuid>.xz.gpg for non-incremental images,
• /backup/home.YYYYMMDD.btrfs_<received_uuid>@<parent_uuid>.xz.gpg for subsequent incremenal images.

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 on the remote side, it is very advisable to take all the security precautions you can. Usually 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 btrbk executable is not needed on the remote side, but you will need "/sbin/btrfs" from the btrfs-progs package.

btrbk comes with a shell script "ssh_filter_btrbk.sh", which restricts ssh access to sane calls to the /sbin/btrfs command needed for snapshot creation and send/receive operations (see ssh_filter_btrbk(1)). Here is an example on how it can be used with ssh:

Step 1 (client): Create a ssh key dedicated to btrbk, without password protection:

ssh-keygen -t rsa -b 2048 -f /etc/btrbk/ssh/id_rsa -C btrbk@mydomain.com -N ""

Step 2 (server): Copy the "ssh_filter_btrbk.sh" from the btrbk project to "/backup/scripts/".

Step 3 (server): Add contents of the public key (/etc/btrbk/ssh/id_rsa.pub) to "/root/.ssh/authorized_keys", and configure "ssh_filter_btrbk.sh" to be executed whenever this key is used for authentication. Example lines:

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

# example backup target (also allowing deletion of old snapshots)
command="/backup/scripts/ssh_filter_btrbk.sh -l --target --delete" <pubkey>...

# example fetch-only backup source (snapshot_preserve_daily=all, snapshot_create=no),
# restricted to subvolumes within /home or /data
command="/backup/scripts/ssh_filter_btrbk.sh -l --send -p /home -p /data" <pubkey>...

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

from="192.168.0.42",command="/backup/scripts/ssh_filter_btrbk.sh [...]" <pubkey>...

Please refer to ssh_filter_btrbk(1) for a description of the "ssh_filter_btrbk.sh" options, as well as sshd(8) for a description of the "authorized_keys" file format.

Also consider setting up ssh access for a user dedicated to btrbk and either set suid root on ssh_filter_btrbk.sh or use the "--sudo" option and configure /etc/sudoers accordingly. For even more security, you can setup a chroot environment in /etc/ssh/sshd_config (see sshd_config(5)).

Restoring Backups

btrbk does not provide any mechanism to restore your backups, this has to be done manually. In the examples below, we assume that you have a btrfs volume mounted at /mnt/btr_pool, and the subvolume you want to have restored is at /mnt/btr_pool/data.

Example: Restore a Snapshot

First, pick a snapshot to be restored:

btrbk list snapshots

From the list, pick the snapshot you want to restore. Let's say it's /mnt/btr_pool/_btrbk_snap/data.20150101.

If the broken subvolume is still present, move it away:

mv /mnt/btr_pool/data /mnt/btr_pool/data.BROKEN

Now restore the snapshot:

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

That's it; your data subvolume is restored. If everything went fine, it's time to nuke the broken subvolume:

btrfs subvolume delete /mnt/btr_pool/data.BROKEN

Example: Restore a Backup

First, pick a backup to be restored:

btrbk list backups

From the list, pick the backup you want to restore. Let's say it's /mnt/btr_backup/data.20150101.

If the broken subvolume is still present, move it away:

mv /mnt/btr_pool/data /mnt/btr_pool/data.BROKEN

Now restore the backup:

btrfs send /mnt/btr_backup/data.20150101 | btrfs receive /mnt/btr_pool/
btrfs subvolume snapshot /mnt/btr_pool/data.20150101 /mnt/btr_pool/data
btrfs subvolume delete /mnt/btr_pool/data.20150101

Alternatively, if you're restoring data on a remote host, do something like this:

btrfs send /mnt/btr_backup/data.20150101 | ssh root@my-remote-host.com btrfs receive /mnt/btr_pool/

If everything went fine, nuke the broken subvolume:

btrfs subvolume delete /mnt/btr_pool/data.BROKEN

FAQ

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

Development

Source Code Repository

The source code for btrbk is managed using Git. Check out the source like this:

git clone git://dev.tty0.ch/btrbk.git

How to Contribute

Your contributions are welcome!

If you would like to contribute or have found bugs:

• Visit the btrbk project page on GitHub and use the issues tracker there.
• Talk to us on Freenode in #btrbk.
• Contact the author via email (the email address can be found in the sources).

Any feedback is appreciated!

License

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