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

  [btrfs-progs]: http://www.kernel.org/pub/linux/kernel/people/kdave/btrfs-progs/
  [Date::Calc]:  http://search.cpan.org/perldoc?Date::Calc

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


  [btrbk source tarball]: http://www.digint.ch/download/btrbk/releases/
  [btrbk debian package]: http://www.digint.ch/download/btrbk/packages/debian/


Synopsis
========

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

  [btrbk(1)]: http://www.digint.ch/btrbk/doc/btrbk.html


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).

  [btrbk.conf(5)]: http://www.digint.ch/btrbk/doc/btrbk.conf.html


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)]).


  [ssh_filter_btrbk(1)]: http://www.digint.ch/btrbk/doc/ssh_filter_btrbk.html
  [sshd(8)]: http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man8/sshd.8
  [sshd_config(5)]: http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man5/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](doc/FAQ.md).
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!

  [btrbk project page on GitHub]: http://github.com/digint/btrbk
  [issues tracker]: http://github.com/digint/btrbk/issues


License
=======

btrbk is free software, available under the [GNU General Public
License, Version 3][GPLv3].

  [GPLv3]: http://www.gnu.org/licenses/gpl.html

