Provided by: btrbk_0.26.0-1_all bug


       btrbk.conf - btrbk configuration file




       The btrbk configuration file specifies which btrfs subvolumes on the filesystem are to be
       processed, what target subvolumes should be used to create the backups, and where the
       snapshots should be generated. The retention policy, as well as most other options can be
       defined either globally or within a section.

       The options specified always apply to the last section encountered, superseding the values
       set in upper-level sections. This means that global options must be set before any
       sections are defined.

       Blank lines are ignored. A hash character (#) starts a comment extending until end of


       volume <volume-directory>|<url>
           Directory of a btrfs volume containing the source subvolume(s) to be backed up.
           <volume-directory> must be an absolute path and point to a btrfs volume (or
           subvolume). Usually the mount point of a btrfs filesystem mounted with the subvolid=0

       subvolume <subvolume-name>
           Subvolume to be backed up, relative to the <volume-directory> specified in the volume
           section. Multiple subvolume sections are allowed within volume sections. Accepts
           wildcard character "*".

       target <type> <target-directory>|<url>
           Target type and directory where the backup subvolumes are to be created. See the
           TARGET TYPES section for supported <type>. Multiple target sections are allowed within
           subvolume sections. A target section defined in the global context or in a volume
           section is propagated (multiplied) to all underlying subvolume sections, unless a
           target with the same declaration already exists (hint: run "btrbk config print" to see
           the resulting configuration).

       For the volume and target sections, you can specify a ssh-url instead of a local
       directory. The syntax for <url> is:


       If a <url> is specified, all access to the filesystem is performed via ssh, using the
       "ssh_" options described below. For convenience, "ssh://<hostname>/<directory>" can also
       be specified as "<hostname>:<directory>".

       Note that btrfs is very picky on file names (mainly for security reasons), only the
       characters [0-9] [a-z] [A-Z] and "._+-@" are allowed.


       The options described here can be specified in global context as well as volume, subvolume
       and target sections, unless stated otherwise.

   Basic Options
       timestamp_format short|long|long-iso
           Timestamp format used as postfix for new snapshot subvolume names. Defaults to

               YYYYMMDD[_N] (e.g. "20150825", "20150825_1")

               YYYYMMDD<T>hhmm[_N] (e.g. "20150825T1531")

               YYYYMMDD<T>hhmmss±hhmm[_N] (e.g. "20150825T153123+0200")

           Note that a postfix "_N" is appended to the timestamp if a snapshot or backup already
           exists with the timestamp of current date/time.

           Use “long-iso” if you want to make sure that btrbk never creates ambiguous time stamps
           (which can happen if multiple snapshots are created during a daylight saving time
           clock change).

           Note that using “long-iso” has implications on the scheduling, see RETENTION POLICY
           (caveats) below.

       snapshot_dir <directory>
           Directory in which the btrfs snapshots are created, relative to <volume-directory> of
           the volume section. Note that btrbk does not autmatically create this directory, and
           the snapshot creation will fail if it is not present.

       snapshot_name <basename>
           Base name of the created snapshot (and backup). This option is only valid in the
           subvolume section. Defaults to <subvolume-name>.

       snapshot_create always|onchange|ondemand|no
           If set to “always”, snapshots are always created. If set to “onchange”, snapshots are
           only created if the source subvolume has changed since the last snapshot (more
           precisely: if the btrfs generation has been increased since the last snapshot). If set
           to “ondemand”, snapshots are only created if the target subvolume is reachable (useful
           if you are tight on disk space and you only need btrbk for backups to an external disk
           which is not always connected). If set to “no”, the snapshots are never created
           (useful if another instance of btrbk is taking care of snapshot creation). Defaults to

       incremental yes|no|strict
           If set, incremental backups are created. If set to “strict”, non-incremental (initial)
           backups are never created. Defaults to “yes”.

   Grouping Options
       group <group-name>[,<group-name>]...
           Add the current section (volume, subvolume or target) to a user-defined group, which
           can be used as filter for most btrbk commands.

   Retention Policy Options
       preserve_day_of_week monday|tuesday|...|sunday
           Defines on what day a backup/snapshot is considered as a weekly backup. Defaults to

       snapshot_preserve no|<retention_policy>
           Set retention policy for snapshots (see RETENTION POLICY below). If set to “no”,
           preserve snapshots according to snapshot_preserve_min only. Defaults to “no”.

       snapshot_preserve_min all|latest|<number>{h,d,w,m,y}
           Preserve all snapshots for a minimum amount of hours (h), days (d), weeks (w), months
           (m) or years (y), regardless of how many there are. If set to “all”, preserve all
           snapshots forever. If set to “latest”, preserve latest snapshot. Defaults to “all”.

       target_preserve no|<retention_policy>
           Set retention policy for backups (see RETENTION POLICY below). If set to “no”,
           preserve backups according to target_preserve_min only. Defaults to “no”.

       target_preserve_min all|latest|no|<number>{h,d,w,m,y}
           Preserve all backups for a minimum amount of hours (h), days (d), weeks (w), months
           (m) or years (y), regardless of how many there are. If set to “all”, preserve all
           backups forever. If set to “latest”, always preserve the latest backup (useful in
           conjunction with "target_preserve no", if you want to keep the latest backup only). If
           set to “no”, only the backups following the target_preserve policy are created.
           Defaults to “all”.

       archive_preserve no|<retention_policy>
           Set retention policy for archives ("btrbk archive" command), with same semantics as

       archive_preserve_min all|latest|no|<number>{h,d,w,m,y}
           Set retention policy for archives ("btrbk archive" command), with same semantics as

   SSH Options
       ssh_identity <file>
           Absolute path to a ssh identity file (private key). Note that if the private key is
           password protected, btrbk will prompt for user input, which is usually not desired.

       ssh_user <username>
           Remote username for ssh. Defaults to “root”. Note that you will have to make sure that
           the remote user is able to run "/sbin/btrfs" (which needs root privileges).

       ssh_port <port>|default
           Port to connect to on the remote host. Defaults to “default” (the port specified in
           ssh_config, which defaults to 22).

       ssh_compression yes|no
           Enables or disables the compression of ssh connections. Defaults to “no”.

       ssh_cipher_spec <cipher_spec>
           Selects the cipher specification for encrypting the session (comma-separated list of
           ciphers in order of preference). See the "-c cipher_spec" option in ssh(1) for more
           information. Defaults to “default” (the ciphers specified in ssh_config).

   Data Stream Options
       stream_compress <compress_command>|no
           Compress the btrfs send stream before transferring it from/to remote locations.
           Defaults to “no”. If enabled, make sure that <compress_command> is available on the
           source and target hosts. Supported <compress_command>: gzip, pigz, bzip2, pbzip2, xz,
           lzo, lz4.

       stream_compress_level default|<number>
           Compression level for the specified <compress_command>. Refer to the related man-page
           for details (usually [1..9], where 1 means fastest compression). Defaults to “default”
           (the default compression level of <compress_command>).

       stream_compress_threads default|<number>
           Number of threads to use for <compress_command>. Only supported for "pigz", "pbzip2"
           and recent versions of "xz".

       stream_buffer <size>|no
           Add a buffer to the btrfs send stream (in front of "btrfs receive"), with a maximum
           size of <size>. This can give a speed improvement (measured up to 20%) on both local
           or remote operations, but also increases system load. A suffix of "k", "m", "g", or
           "%" can be added to <size> to denote kilobytes (*1024), megabytes, gigabytes, or a
           percentage of total physical memory. Defaults to “no”. If enabled, make sure that the
           "mbuffer" command is available on the target host.

       rate_limit <rate>|no
           Limit the transfer to a maximum of <rate> bytes per second. A suffix of "k", "m", "g",
           or "t" can be added to denote kilobytes (*1024), megabytes, and so on. Defaults to
           “no”. If enabled for remote sources, make sure that the "pv" command is available on
           the source host.

   System Options
       transaction_log <file>|no
           If set, all transactions (snapshot create, subvolume send-receive, subvolume delete)
           as well as abort messages are logged to <file>, in a space-separated table format:
           "localtime type status target_url source_url parent_url message".

       transaction_syslog <facility>|no
           If set, all transactions (as described in transaction_log above) are logged to syslog.
           The program name used in the messages is "btrbk". Accepted parameters for <facility>:
           user, mail, daemon, auth, lpr, news, cron, authpriv, local0..local7.

       lockfile <file>|no
           Create lockfile <file> on startup; checks lockfile before running any btrfs commands
           (using perl "flock"), and exits if the lock is held by another btrbk instance. Ignored
           on dryrun (-n, --dry-run). See also --lockfile command-line option.

       backend btrfs-progs|btrfs-progs-btrbk|btrfs-progs-sudo
           Backend filesystem utilities to be used for btrfs specific operations. The default
           “btrfs-progs” simply executes btrfs(8) commands groups (e.g. "btrfs subvolume show").

               Default backend, btrfs commands are called as specified in btrfs(8) (e.g. "btrfs
               subvolume show").

               btrfs commands are separated by a dash instead of a whitespace (e.g.
               "btrfs-subvolume-show" instead of "btrfs subvolume show"). Useful for setting suid
               or file capabilities (setcap) on specific btrfs commands, as implemented in

               btrfs commands are prefixed with "sudo -n" (e.g. "sudo -n btrfs subvolume show"
               instead of "btrfs subvolume show"). Make sure to have apropriate (root)
               permissions for "btrfs" command groups in /etc/sudoers.

           For convenience, it is also possible to set backend_local or backend_remote options,
           which will override the backend only for local or remote sources/targets (e.g.
           "backend_remote btrfs-progs-btrbk").

   Btrfs Specific Options
       btrfs_commit_delete after|each|no
           If set, make sure the deletion of snapshot and backup subvolumes are committed to disk
           when btrbk terminates. Defaults to “no”.

       snapshot_qgroup_destroy yes|no *experimental*

       target_qgroup_destroy yes|no *experimental*

       archive_qgroup_destroy yes|no *experimental*
           Whenever a subvolume is deleted, also destroy corresponding default qgroup
           "0/<subvol-id>". Only useful if you have enabled btrfs quota support. See also:


       btrbk uses separate retention policies for snapshots and backups, which are defined by the
       snapshot_preserve_min, snapshot_preserve, target_preserve_min, target_preserve, and
       preserve_day_of_week configuration options.

       Within this section, any statement about "backups" is always valid for backups as well as
       snapshots, referring to target_preserve or snapshot_preserve respectively.

       The format for <retention_policy> is:

           [<hourly>h] [<daily>d] [<weekly>w] [<monthly>m] [<yearly>y]

       With the following semantics:

           Defines how many hours back hourly backups should be preserved. The first backup of an
           hour is considered an hourly backup. Note that if you use <hourly> scheduling, make
           sure to also set timestamp_format to “long” or “long-iso”, or the scheduler will
           interpret the time as "00:00" (midnight).

           Defines how many days back daily backups should be preserved. The first backup of a
           day is considered a daily backup.

           Defines how many weeks back weekly backups should be preserved. The first daily backup
           created at preserve_day_of_week (or the first backup in this week if none was made on
           the exact day) is considered as a weekly backup.

           Defines how many months back monthly backups should be preserved. Every first weekly
           backup in a month is considered a monthly backup.

           Defines for how many years back yearly backups should be preserved. Every first
           monthly backup in a year is considered a yearly backup.

       Use an asterisk for “all” (e.g. "target_preserve 60d *m" states: "preserve daily backups
       for 60 days back, and all monthly backups").

       The reference time (which defines the beginning of a day, week, month or year) for all
       date/time calculations is the local time of the host running btrbk.


       ·   If you run a setup with several btrbk instances (e.g. one snapshot-only instance per
           remote client, and a separate fetch-only instance on the backup server), it makes
           perfectly sense to run btrbk with different local time on the clients, in order to
           make sure the backups from all the remote hosts are preserved for "midnight", and not
           at "00:00 UTC" (which would be "14:00" in Honolulu). If you want this behaviour, do
           NOT use "timestamp_format long-iso".

       ·   If "timestamp_format long-iso" is set, running btrbk from different time zones leads
           to different interpretation of "first in day, week, month, or year". Make sure to run
           btrbk with the same time zone on every host, e.g. by setting the TZ environment
           variable (see tzset(3)).


           Backup to a btrfs filesystem, using "btrfs send/receive". This is the recommended
           (standard) target type. The <target-directory> must be an absolute path and point to a
           btrfs volume (or subvolume), or to a directory within a subvolume. See btrfs-send(8),

       raw *experimental*
           Backup to a raw (filesystem independent) file from the output of btrfs-send(8), with
           optional compression and encryption.

           Note that the target preserve mechanism is currently disabled for incremental raw
           backups (btrbk does not delete any incremental raw files)!

           Raw backups consist of two files: the main data file containing the btrfs send stream,
           and a sidecar file ".info" containing metadata:


           For incremental backups ("incremental yes"), please note that:

           ·   As soon as a single incremental backup file is lost or corrupted, all later
               incremental backups become invalid, as there is no common parent for the
               subsequent incremental images anymore. This might be a good compromise for a
               vacation backup plan, but for the long term make sure that a non-incremental
               backup is triggered from time to time.

           ·   There is currently no support for rotation of incremental backups: if incremental
               is set, a full backup must be triggered manually from time to time in order to be
               able to delete old backups.

           Additional options for raw targets:

           raw_target_compress <compress_command>|no
               Compression algorithm to use for raw backup target. Supported <compress_command>:
               gzip, pigz, bzip2, pbzip2, xz, lzo, lz4.

           raw_target_compress_level default|<number>
               Compression level for the specified <compress_command>.

           raw_target_compress_threads default|<number>
               Number of threads to use for <compress_command>.

           raw_target_split <size>|no
                Split the raw backup file into pieces of size <size>.

           raw_target_block_size <number>
               Block size to use for writing the raw backup file. Defaults to “128K”.

           raw_target_encrypt gpg|openssl_enc|no
               If enabled, encrypt the target raw file using gpg or openssl_enc.

           Additional options for "raw_target_encrypt gpg":

           gpg_keyring <file>
               Keyring to use for gpg, e.g. "/etc/btrbk/gpg/pubring.kbx".

           gpg_recipient <name>
               Encrypt for user id <name> (email address).

           Additional options for "raw_target_encrypt openssl_enc" (very experimental):

           openssl_ciphername <name>
               Defaults to “aes-256-cbc”.

           openssl_iv_size <size-in-bytes>|no
               Depends on selected cipher.

           openssl_keyfile <file>|no
               Point to a key file in hex (absolute path). Example key file creation (256bit

                     # dd if=/dev/urandom bs=1 count=32 \
                       | od -x -A n \
                       | tr -d "[:space:]" > /path/to/keyfile

           kdf_backend <file>|no
               KDF backend to be executed, e.g. "/usr/share/btrbk/scripts/".

           kdf_keysize <size-in-bytes>
               Defaults to “32”.

           kdf_keygen once|each
               Defaults to “once”.


       Please refer to the btrbk project page for further details.




       Axel Burri <>