Provided by: btrbk_0.27.1-1_all 
NAME
btrbk.conf - btrbk configuration file
SYNOPSIS
/etc/btrbk.conf
/etc/btrbk/btrbk.conf
DESCRIPTION
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 line.
SECTIONS
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=5 option.
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 "*".
If set to ".", the subvolume at <volume-directory> is used as backup source, and the snapshots will
be created within the source subvolume itself (see snapshot_dir option below), which is not
recommended. Note that if this subvolume is btrfs root (id=5), it needs to have a valid UUID, which
is not the case for file systems created with btrfs-progs < 4.16.
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).
<target-directory>
Run actions locally.
Note that whitespace or unicode characters are NOT allowed for file names. Allowed characters are:
[0-9] [a-z] [A-Z] and "._+-@"
This is for sanity/safety/security reasons, we apologize for the inconvenience.
<url>
Run actions remotely via ssh. Either:
ssh://<hostname>/<directory>
<hostname>:<directory>
If a <url> is specified, btrbk actions for <hostname> (shell commands) are executed via ssh, using
the "ssh_" options described below.
Note that btrbk keeps mountpoint and btrfs-tree information per hostname: specifying different
ssh_port for the same host, e.g. for several virtual machines listening on same address, will NOT
work. If you need this, define alias host names for each vm.
OPTIONS
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 “short”.
short
YYYYMMDD[_N] (e.g. "20150825", "20150825_1")
long
YYYYMMDD<T>hhmm[_N] (e.g. "20150825T1531")
long-iso
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 at least
one 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
“always”.
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. This option can be set multiple times within the same context.
Retention Policy Options
preserve_day_of_week monday|tuesday|...|sunday
Defines on what day a snapshot/backup is considered to be a "weekly" backup. Weekly, monthly and
yearly backups are preserved on this day of week (see RETENTION POLICY below). Defaults to “sunday”.
preserve_hour_of_day [0..23]
Defines after what time (in full hours since midnight) a snapshot/backup is considered to be a
"daily" backup. Daily, weekly, monthly and yearly backups are preserved on this hour (see RETENTION
POLICY below). If you set this option, make sure to also set timestamp_format to “long” or “long-iso”
(backups and snapshots having no time information will ignore this option). Defaults to “0”.
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 target_preserve.
archive_preserve_min all|latest|no|<number>{h,d,w,m,y}
Set retention policy for archives ("btrbk archive" command), with same semantics as
target_preserve_min.
archive_exclude <pattern> *experimental*
Exclude subvolumes matching <pattern> from archiving. The pattern accepts wildcard character "*", and
is matched against the end of the pathname.
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”. Make sure the remote user is able to run "btrfs" with
root privileges (see option backend for details).
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).
Note that btrbk keeps mountpoint and btrfs-tree information per hostname: specifying different
ssh_port for the same host, e.g. for several virtual machines listening on same address, will NOT
work. If you need this, define alias host names for each vm.
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. Defaults to “btrfs-progs”.
btrfs-progs
Default backend, btrfs commands are called as specified in btrfs(8) (e.g. "btrfs subvolume
show").
btrfs-progs-btrbk
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 https://github.com/digint/btrfs-progs-btrbk.
btrfs-progs-sudo
btrfs commands are prefixed with "sudo -n" (e.g. "sudo -n btrfs subvolume show" instead of "btrfs
subvolume show"). Make sure to have appropriate (root) permissions for the "btrfs" command groups
and the "readlink" command 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:
https://bugzilla.kernel.org/show_bug.cgi?id=91751
RETENTION POLICY
btrbk uses separate retention policies for snapshots and backups, which are defined by the
snapshot_preserve_min, snapshot_preserve, target_preserve_min, target_preserve, preserve_day_of_week and
preserve_hour_of_day 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:
hourly
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).
daily
Defines how many days back daily backups should be preserved. The first backup of a day (starting at
preserve_hour_of_day) is considered a daily backup.
weekly
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.
monthly
Defines how many months back monthly backups should be preserved. Every first weekly backup in a
month is considered a monthly backup.
yearly
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.
Hint: Run btrbk with the -S, --print-schedule option to get a comprehensive output of the scheduler
results.
Caveats:
• 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)).
TARGET TYPES
send-receive
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), btrfs-receive(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:
<snapshot-name>.<timestamp>[_N].btrfs[.gz|.bz2|.xz][.gpg]
<snapshot-name>.<timestamp>[_N].btrfs[.gz|.bz2|.xz][.gpg].info
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 key):
# 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_pbkdf2.py".
kdf_keysize <size-in-bytes>
Defaults to “32”.
kdf_keygen once|each
Defaults to “once”.
AVAILABILITY
Please refer to the btrbk project page https://digint.ch/btrbk/ for further details.
SEE ALSO
btrbk(1)
AUTHOR
Axel Burri <axel@tty0.ch>
Btrbk 2018-12-05 BTRBK.CONF(5)