btrbk/doc/btrbk.conf.5

'\" t
.\"     Title: btrbk.conf
.\"    Author: [see the "AUTHOR(S)" section]
.\" Generator: Asciidoctor 1.5.7.1
.\"      Date: 2019-04-24
.\"    Manual: Btrbk Manual
.\"    Source: Btrbk 0.28.0
.\"  Language: English
.\"
.TH "BTRBK.CONF" "5" "2019-04-24" "Btrbk 0.28.0" "Btrbk Manual"
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.SH "NAME"
btrbk.conf \- btrbk configuration file
.SH "SYNOPSIS"
.sp
.nf
/etc/btrbk.conf
/etc/btrbk/btrbk.conf
.fi
.br
.SH "DESCRIPTION"
.sp
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.
.sp
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.
.sp
Blank lines are ignored. A hash character (#) starts a comment
extending until end of line.
.sp
Whitespace or unicode characters are not allowed for file
names. Allowed characters are:
.sp
.if n .RS 4
.nf
[0\-9] [a\-z] [A\-Z] and "._+\-@"
.fi
.if n .RE
.sp
This is for sanity/safety/security reasons, we apologize for the
inconvenience.
.SH "SECTIONS"
.sp
\fBvolume\fP <volume\-directory>|<url>
.RS 4
Directory of a btrfs volume containing the source subvolume(s) to
be backed up. \fI<volume\-directory>\fP must be an absolute path and
point to a btrfs volume (or subvolume). Usually the mount point of
a btrfs filesystem mounted with the \fIsubvolid=5\fP option.
.RE
.sp
\fBsubvolume\fP <subvolume\-name>
.RS 4
Subvolume to be backed up, relative to the \fI<volume\-directory>\fP
specified in the \fIvolume\fP section. Multiple \fIsubvolume\fP sections
are allowed within \fIvolume\fP sections. Accepts wildcard character
"*".
.sp
If set to ".", the subvolume at \fI<volume\-directory>\fP is used as backup
source, and the snapshots will be created within the source subvolume
itself (see \fIsnapshot_dir\fP 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.
.RE
.sp
\fBtarget\fP [send\-receive|raw] <target\-directory>|<url>
.RS 4
Target directory where the backup subvolumes are to be
created. The optional target type defaults to \(lqsend\-receive\(rq,
see TARGET TYPES below for details.
.sp
Multiple \fItarget\fP sections are allowed, in any context: a \fItarget\fP
defined in \fIvolume\fP or global context will be used for all underlying
\fIsubvolume\fP sections (hint: run "btrbk list" or "btrbk config print"
to see the resulting configuration).
.RE
.sp
If a \fI<url>\fP is specified, btrbk actions (shell commands) are executed
remotely via ssh, using the SSH Options described
below. Accepted formats are:
.sp
.if n .RS 4
.nf
ssh://<hostname>[:<port>]/<directory>
<hostname>:<directory>
.fi
.if n .RE
.sp
If you are connecting to virtual machines, consider configuring
several \fIvolume\fP sections for a \fI<hostname>\fP, with distinct \fI<port>\fP
numbers for each machine.
.SH "OPTIONS"
.sp
The options described here can be specified in \fIglobal context\fP as
well as \fIvolume\fP, \fIsubvolume\fP and \fItarget\fP sections, unless stated
otherwise.
.SS "Basic Options"
.sp
\fBtimestamp_format\fP short|long|long\-iso
.RS 4
Timestamp format used as postfix for new snapshot subvolume
names. Defaults to \(lqshort\(rq.
.sp
\fBshort\fP
.RS 4
\f(CRYYYYMMDD[_N]\fP  (e.g. "20150825", "20150825_1")
.RE
.sp
\fBlong\fP
.RS 4
\f(CRYYYYMMDD<T>hhmm[_N]\fP  (e.g. "20150825T1531")
.RE
.sp
\fBlong\-iso\fP
.RS 4
\f(CRYYYYMMDD<T>hhmmss&plusmn;hhmm[_N]\fP  (e.g. "20150825T153123+0200")
.RE
.sp
Note that a postfix "_N" is appended to the timestamp if a snapshot or
backup already exists with the timestamp of current date/time.
.sp
Use \(lqlong\-iso\(rq 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).
.sp
Note that using \(lqlong\-iso\(rq has implications on the scheduling, see
RETENTION POLICY (caveats) below.
.RE
.sp
\fBsnapshot_dir\fP <directory>
.RS 4
Directory in which the btrfs snapshots are created, relative to
\fI<volume\-directory>\fP of the \fIvolume\fP section. Note that btrbk does
not autmatically create this directory, and the snapshot creation
will fail if it is not present.
.RE
.sp
\fBsnapshot_name\fP <basename>
.RS 4
Base name of the created snapshot (and backup). This option is
only valid in the \fIsubvolume\fP section. Defaults to
\fI<subvolume\-name>\fP.
.RE
.sp
\fBsnapshot_create\fP always|onchange|ondemand|no
.RS 4
If set to \(lqalways\(rq, snapshots are always created. If set to
\(lqonchange\(rq, 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
\(lqondemand\(rq, 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 \(lqno\(rq, the snapshots are never
created (useful if another instance of btrbk is taking care of
snapshot creation). Defaults to \(lqalways\(rq.
.RE
.sp
\fBincremental\fP yes|no|strict
.RS 4
If set, incremental backups are created. If set to \(lqstrict\(rq,
non\-incremental (initial) backups are never created, and
incremental backups are restricted to \fIrelated parents\fP (by
parent\-uuid relationship). Defaults to \(lqyes\(rq.
.sp
Note that even if the parent\-uuid chain is broken, snapshots and
backups can still share data (which is especially true for backups
created with \fIincremental\fP option enabled), and are perfectly suitable
as parents for incremental send\-receive operations. But as btrbk can
not be certain about this, such operations are disallowed in
"incremental strict" mode.
.RE
.sp
\fBnoauto\fP yes|no
.RS 4
If set, the context is skipped by all btrbk actions unless
explicitely enabled by a matching btrbk \fI<filter>\fP command line
argument (e.g. "btrbk run myfilter").
.RE
.SS "Grouping Options"
.sp
\fBgroup\fP <group\-name> [<group\-name>]...
.RS 4
Add the current section (volume, subvolume or target) to
user\-defined groups, which can be used as filter for most btrbk
commands. This option can be set multiple times within the same
context.
.RE
.SS "Retention Policy Options"
.sp
\fBpreserve_day_of_week\fP monday|tuesday|...|sunday
.RS 4
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 \(lqsunday\(rq.
.RE
.sp
\fBpreserve_hour_of_day\fP [0..23]
.RS 4
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 \fItimestamp_format\fP to \(lqlong\(rq or
\(lqlong\-iso\(rq (backups and snapshots having no time information
will ignore this option). Defaults to \(lq0\(rq.
.RE
.sp
\fBsnapshot_preserve\fP no|<retention_policy>
.RS 4
Set retention policy for snapshots (see
RETENTION POLICY below). If set to \(lqno\(rq,
preserve snapshots according to \fIsnapshot_preserve_min\fP
only. Defaults to \(lqno\(rq.
.RE
.sp
\fBsnapshot_preserve_min\fP all|latest|<number>{h,d,w,m,y}
.RS 4
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 \(lqall\(rq, preserve all snapshots forever. If
set to \(lqlatest\(rq, preserve latest snapshot. Defaults to \(lqall\(rq.
.RE
.sp
\fBtarget_preserve\fP no|<retention_policy>
.RS 4
Set retention policy for backups (see
RETENTION POLICY below). If set to \(lqno\(rq,
preserve backups according to \fItarget_preserve_min\fP only. Defaults
to \(lqno\(rq.
.RE
.sp
\fBtarget_preserve_min\fP  all|latest|no|<number>{h,d,w,m,y}
.RS 4
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 \(lqall\(rq, preserve all backups forever. If set to
\(lqlatest\(rq, always preserve the latest backup (useful in
conjunction with "target_preserve no", if you want to keep the
latest backup only). If set to \(lqno\(rq, only the backups following
the \fItarget_preserve\fP policy are created. Defaults to \(lqall\(rq.
.RE
.sp
\fBarchive_preserve\fP no|<retention_policy>
.RS 4
Set retention policy for archives ("btrbk archive" command), with
same semantics as \fItarget_preserve\fP.
.RE
.sp
\fBarchive_preserve_min\fP all|latest|no|<number>{h,d,w,m,y}
.RS 4
Set retention policy for archives ("btrbk archive" command), with
same semantics as \fItarget_preserve_min\fP.
.RE
.sp
\fBarchive_exclude\fP <pattern>
.RS 4
Exclude subvolumes matching <pattern> from archiving. The pattern
accepts wildcard character "*", and is matched against the end of
the pathname.
.RE
.SS "SSH Options"
.sp
\fBssh_identity\fP <file>
.RS 4
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.
.RE
.sp
\fBssh_user\fP <username>
.RS 4
Remote username for ssh. Defaults to \(lqroot\(rq. Make sure the
remote user is able to run "btrfs" with root privileges (see
option \fIbackend\fP for details).
.RE
.sp
\fBssh_compression\fP yes|no
.RS 4
Enables or disables the compression of ssh connections. Defaults
to \(lqno\(rq.
.RE
.sp
\fBssh_cipher_spec\fP <cipher_spec>
.RS 4
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 \(lqdefault\(rq (the ciphers specified in \fIssh_config\fP).
.RE
.sp
Previous versions btrbk allowed you to set a \fBssh_port\fP option, this
has been dropped in favor of the \f(CRssh://hostname:port\fP notation in the
\fIvolume\fP and \fItarget\fP sections. If you want to set a
global port for all SSH connections to remote hosts, set the \(lqPort\(rq
option in ssh_config(5).
.SS "Data Stream Options"
.sp
\fBstream_compress\fP <compress_command>|no
.RS 4
Compress the btrfs send stream before transferring it from/to
remote locations. Defaults to \(lqno\(rq. If enabled, make sure that
\fI<compress_command>\fP is available on the source and target
hosts. Supported \fI<compress_command>\fP: gzip, pigz, bzip2, pbzip2,
xz, lzo, lz4.
.RE
.sp
\fBstream_compress_level\fP default|<number>
.RS 4
Compression level for the specified \fI<compress_command>\fP. Refer to
the related man\-page for details (usually [1..9], where 1 means
fastest compression). Defaults to \(lqdefault\(rq (the default
compression level of \fI<compress_command>\fP).
.RE
.sp
\fBstream_compress_threads\fP default|<number>
.RS 4
Number of threads to use for <compress_command>. Only supported
for "pigz", "pbzip2" and recent versions of "xz".
.RE
.sp
\fBstream_buffer\fP <size>|no
.RS 4
Add a buffer to the btrfs send stream (in front of "btrfs
receive"), with a maximum size of \fI<size>\fP. 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 \fI<size>\fP to denote kilobytes (*1024),
megabytes, gigabytes, or a percentage of total physical
memory. Defaults to \(lqno\(rq.
.sp
If enabled, make sure that the "mbuffer" command is available on the
target host. Note that versions of mbuffer < 20180505 suffered from
nasty bugs (infinite loops, hangs); if your main concern is a stable
backup process, leave this option disabled.
.RE
.sp
\fBrate_limit\fP <rate>|no
.RS 4
Limit the transfer to a maximum of \fI<rate>\fP bytes per second. A
suffix of "k", "m", "g", or "t" can be added to denote kilobytes
(*1024), megabytes, and so on. Defaults to \(lqno\(rq. If enabled for
remote sources, make sure that the "pv" command is available on
the source host.
.RE
.SS "System Options"
.sp
\fBtransaction_log\fP <file>|no
.RS 4
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".
.RE
.sp
\fBtransaction_syslog\fP  <facility>|no
.RS 4
If set, all transactions (as described in \fItransaction_log\fP above)
are logged to syslog. The program name used in the messages is
"btrbk".  Accepted parameters for \fI<facility>\fP: user, mail,
daemon, auth, lpr, news, cron, authpriv, local0..local7.
.RE
.sp
\fBlockfile\fP <file>|no
.RS 4
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 (\fI\-n\fP,
\fI\-\-dry\-run\fP). See also \fI\-\-lockfile\fP command\-line option.
.RE
.sp
\fBbackend\fP btrfs\-progs|btrfs\-progs\-btrbk|btrfs\-progs\-sudo
.RS 4
Backend filesystem utilities to be used for btrfs specific
operations. Defaults to \(lqbtrfs\-progs\(rq.
.sp
btrfs\-progs
.RS 4
Default backend, btrfs commands are called as specified in
btrfs(8) (e.g. "btrfs subvolume show").
.RE
.sp
btrfs\-progs\-btrbk
.RS 4
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
.URL "https://github.com/digint/btrfs\-progs\-btrbk" "" "."
.RE
.sp
btrfs\-progs\-sudo
.RS 4
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.
.RE
.sp
For convenience, it is also possible to set \fBbackend_local\fP or
\fBbackend_remote\fP options, which will override the backend only for
local or remote sources/targets (e.g. "backend_remote
btrfs\-progs\-btrbk").
.RE
.SS "Btrfs Specific Options"
.sp
\fBbtrfs_commit_delete\fP after|each|no
.RS 4
If set, make sure the deletion of snapshot and backup subvolumes
are committed to disk when btrbk terminates. Defaults to \(lqno\(rq.
.RE
.sp
\fBincremental_clones\fP <number>
.RS 4
Maximum number of clone sources allowed for incremental send. If
set, btrbk adds "\-c <clone\-src>" to the btrfs\-send(8) command for
all present snapshot/backup pairs (correlated subvolumes matching
matching \fIreceived_uuid\fP, printed by "btrbk stats"). Set this to a
high number if you want to make sure that no common data is missed
on incremental backups, in expense of btrfs\-send
performance. Defaults to 0.
.RE
.sp
\fBincremental_resolve\fP mountpoint|directory
.RS 4
Specifies where to search for the best common parent for
incremental backups. If set to \(lqmountpoint\(rq, use parents in the
filesystem tree below mount points of source
"<volume\-directory>/<snapshot\-dir>" and target
"<target\-directory>". If set to \(lqdirectory\(rq, use parents
strictly below source/target directories. Set this to
\(lqdirectory\(rq if you get access problems (when not running btrbk
as root). Defaults to \(lqmountpoint\(rq.
.RE
.sp
\fBsnapshot_qgroup_destroy\fP yes|no  \fI*experimental*\fP
.RS 4

.RE
.sp
\fBtarget_qgroup_destroy\fP yes|no  \fI*experimental*\fP
.RS 4

.RE
.sp
\fBarchive_qgroup_destroy\fP yes|no  \fI*experimental*\fP
.RS 4
Whenever a subvolume is deleted, also destroy corresponding
default qgroup "\f(CR0/<subvol\-id>\fP". Only useful if you have enabled
btrfs quota support. See also:
.URL "https://bugzilla.kernel.org/show_bug.cgi?id=91751" "" ""
.RE
.SH "RETENTION POLICY"
.sp
btrbk uses separate retention policies for snapshots and backups,
which are defined by the \fIsnapshot_preserve_min\fP, \fIsnapshot_preserve\fP,
\fItarget_preserve_min\fP, \fItarget_preserve\fP, \fIpreserve_day_of_week\fP and
\fIpreserve_hour_of_day\fP configuration options.
.sp
Within this section, any statement about "backups" is always valid for
backups as well as snapshots, referring to \fItarget_preserve\fP or
\fIsnapshot_preserve\fP respectively.
.sp
The format for \fI<retention_policy>\fP is:
.sp
.if n .RS 4
.nf
[<hourly>h] [<daily>d] [<weekly>w] [<monthly>m] [<yearly>y]
.fi
.if n .RE
.sp
With the following semantics:
.sp
\fBhourly\fP
.RS 4
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 \fItimestamp_format\fP to \(lqlong\(rq or \(lqlong\-iso\(rq, or the
scheduler will interpret the time as "00:00" (midnight).
.RE
.sp
\fBdaily\fP
.RS 4
Defines how many days back daily backups should be preserved. The
first backup of a day (starting at \fIpreserve_hour_of_day\fP) is
considered a daily backup.
.RE
.sp
\fBweekly\fP
.RS 4
Defines how many weeks back weekly backups should be
preserved. The first daily backup created at
\fIpreserve_day_of_week\fP (or the first backup in this week if none
was made on the exact day) is considered as a weekly backup.
.RE
.sp
\fBmonthly\fP
.RS 4
Defines how many months back monthly backups should be
preserved. Every first weekly backup in a month is considered a
monthly backup.
.RE
.sp
\fByearly\fP
.RS 4
Defines for how many years back yearly backups should be
preserved. Every first monthly backup in a year is considered a
yearly backup.
.RE
.sp
Use an asterisk for \(lqall\(rq (e.g. "target_preserve 60d *m"
states: "preserve daily backups for 60 days back, and all monthly
backups").
.sp
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.
.sp
Hint: Run btrbk with the \fI\-S\fP, \fI\-\-print\-schedule\fP option to get a
comprehensive output of the scheduler results.
.sp
Caveats:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.  sp -1
.  IP \(bu 2.3
.\}
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".
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.  sp -1
.  IP \(bu 2.3
.\}
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)).
.RE
.SH "TARGET TYPES"
.sp
\fBsend\-receive\fP
.RS 4
Backup to a btrfs filesystem, using "btrfs send/receive". This is
the recommended (standard) target type. The \fI<target\-directory>\fP
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).
.RE
.sp
\fBraw\fP  \fI*experimental*\fP
.RS 4
Backup to a raw (filesystem independent) file from the output of
btrfs\-send(8), with optional compression and encryption.
.sp
Note that the target preserve mechanism is currently disabled for
incremental raw backups (btrbk does not delete any incremental raw
files)!
.sp
Raw backups consist of two files: the main data file containing the
btrfs send stream, and a sidecar file ".info" containing metadata:
.sp
.if n .RS 4
.nf
<snapshot\-name>.<timestamp>[_N].btrfs[.gz|.bz2|.xz][.gpg]
<snapshot\-name>.<timestamp>[_N].btrfs[.gz|.bz2|.xz][.gpg].info
.fi
.if n .RE
.sp
For \fIincremental\fP backups ("incremental yes"), please note that:
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.  sp -1
.  IP \(bu 2.3
.\}
As soon as a single \fIincremental\fP 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.
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.  sp -1
.  IP \(bu 2.3
.\}
There is currently no support for rotation of incremental backups:
if \fIincremental\fP is set, a full backup must be triggered manually
from time to time in order to be able to delete old backups.
.RE
.sp
Additional options for raw targets:
.sp
\fBraw_target_compress\fP <compress_command>|no
.RS 4
Compression algorithm to use for raw backup target. Supported
\fI<compress_command>\fP: gzip, pigz, bzip2, pbzip2, xz, lzo, lz4.
.RE
.sp
\fBraw_target_compress_level\fP default|<number>
.RS 4
Compression level for the specified <compress_command>.
.RE
.sp
\fBraw_target_compress_threads\fP default|<number>
.RS 4
Number of threads to use for <compress_command>.
.RE
.sp
\fBraw_target_split\fP <size>|no
.RS 4
Split the raw backup file into pieces of size \fI<size>\fP.
.RE
.sp
\fBraw_target_block_size\fP <number>
.RS 4
Block size to use for writing the raw backup file. Defaults to
\(lq128K\(rq.
.RE
.sp
\fBraw_target_encrypt\fP gpg|openssl_enc|no
.RS 4
If enabled, encrypt the target raw file using gpg or openssl_enc.
.RE
.sp
Additional options for "raw_target_encrypt gpg":
.sp
\fBgpg_keyring\fP <file>
.RS 4
Keyring to use for gpg, e.g. "\f(CR/etc/btrbk/gpg/pubring.kbx\fP".
.RE
.sp
\fBgpg_recipient\fP <name>
.RS 4
Encrypt for user id \fI<name>\fP (email address).
.RE
.sp
Additional options for "raw_target_encrypt openssl_enc" (\fIvery
experimental\fP):
.sp
\fBopenssl_ciphername\fP\~<name>
.RS 4
Defaults to \(lqaes\-256\-cbc\(rq.
.RE
.sp
\fBopenssl_iv_size\fP <size\-in\-bytes>|no
.RS 4
Depends on selected cipher.
.RE
.sp
\fBopenssl_keyfile\fP <file>|no
.RS 4
Point to a key file in hex (absolute path). Example key file
creation (256bit key):
.sp
.if n .RS 4
.nf
  # dd if=/dev/urandom bs=1 count=32 \(rs
    | od \-x \-A n \(rs
    | tr \-d "[:space:]" > /path/to/keyfile
.fi
.if n .RE
.RE
.sp
\fBkdf_backend\fP <file>|no
.RS 4
KDF backend to be executed,
e.g. "\f(CR/usr/share/btrbk/scripts/kdf_pbkdf2.py\fP".
.RE
.sp
\fBkdf_keysize\fP <size\-in\-bytes>
.RS 4
Defaults to \(lq32\(rq.
.RE
.sp
\fBkdf_keygen\fP once|each
.RS 4
Defaults to \(lqonce\(rq.
.RE
.RE
.SH "AVAILABILITY"
.sp
Please refer to the btrbk project page \fB\c
.URL "https://digint.ch/btrbk/" "" "\fP"
for further details.
.SH "SEE ALSO"
.sp
\fBbtrbk\fP(1)
.SH "AUTHOR"
.sp
Axel Burri <\c
.MTO "axel\(attty0.ch" "" ">"