Ubuntu Manpage: btrbk - backup tool for btrfs subvolumes

NAME

       btrbk - backup tool for btrfs subvolumes

SYNOPSIS

       btrbk [-h|--help] [--version]
             [-c|--config <file>] [-n|--dry-run] [--exclude <filter>]
             [-p|--preserve] [--preserve-snapshots] [--preserve-backups]
             [-v|--verbose] [-q|--quiet] [-l|--loglevel <level>]
             [-t|--table] [-L|--long] [-1|--single-column]
             [--format <output-format>] [--pretty]
             [-S|--print-schedule] [--progress]
             [--lockfile <file>]
             [--override <config_option>=<value>]
             <command> [[--] <filter>...]

DESCRIPTION

btrbk is a backup tool for btrfs subvolumes, taking advantage of btrfs specific capabilities to create
atomic snapshots and transfer them incrementally to a target btrfs filesystem. It is able to perform
backups from one source to multiple destinations.

For most operations, btrbk requires root privileges to run correctly. Alternatively, consider using
"btrfs-progs-sudo" or "btrfs-progs-btrbk" backends, both of which allows you to run btrbk as a regular
user. Refer to configuration option backend in btrbk.conf(5) for more details.

Snapshots and Backups
Snapshots as well as backup subvolumes are created in the form:

<snapshot-name>.<timestamp>[_N]

Where <snapshot-name> is identical to the source subvolume name, unless the configuration option
snapshot_name is set. <timestamp> is a timestamp describing the creation time (local time of the host
running btrbk) of the snapshot/backup. The format can be configured using the timestamp_format option,
refer to btrbk.conf(5) for details. If multiple snapshots/backups are created on the same date/time, N
will be incremented on each snapshot, starting at 1.

If a snapshot or backup does not match the naming scheme above (e.g. if it has been renamed manually),
btrbk will leave it untouched.

Note that in btrfs terminology, a snapshot is a “subvolume with a given initial content of the original
subvolume” (showing a parent-uuid, see btrfs-subvolume(8)), and they can be read-write (default) or
read-only. In btrbk terminology, snapshot means “read-only btrfs snapshot”, and backup means “read-only
subvolume created with send/receive” (showing a received-uuid).

OPTIONS

       -h, --help
           Prints the synopsis and a list of the commands.

       --version
           Prints the btrbk version.

       -c, --config <file>
           Read the configuration from <file>.

       -n, --dry-run
           Don’t run anything that would alter the filesystem, just show the snapshots and backup subvolumes
           that would be created/deleted by the run, snapshot, resume, prune, archive and clean commands. Use in
           conjunction with -l debug to see the btrfs commands that would be executed.

       --exclude <filter>
           Exclude configured sections matching <filter>. See FILTER STATEMENTS below.

       -p, --preserve
           Preserve all snapshots and backups. Skips deletion of any snapshots and backups, even if specified in
           the configuration file (shortcut for "--preserve-snapshots --preserve-backups").

       --preserve-snapshots
           Preserve all snapshots. Skips deletion of any snapshots, even if specified in the configuration file.

       --preserve-backups
           Preserve all backups. Skips deletion of any backups, even if specified in the configuration file.

       --wipe
           Ignore configured snapshot retention policy, delete all but the latest snapshots instead. All
           snapshots needed for incremental backup (latest common) are also preserved. Useful if you are getting
           low on disk space (ENOSPC).

       -v, --verbose
           Increase the logging level, see "--loglevel".

       -q, --quiet
           Quiet operation. If set, btrbk does not print the summary after executing the run, snapshot, resume,
           prune, or archive commands.

       -l, --loglevel <level>
           Set the level of verbosity for the stderr logging. Accepted levels are: error, warn, info, debug, and
           trace. Default is info.

       -t, --table
           Print output in table format (shortcut for "--format=table").

       -L, --long
           Print output in long table format (shortcut for "--format=long").

       -1, --single-column
           Print output as single column (not available for all commands).

       --format table|long|raw|col:[h:]<columns>
           Print output in specified format. If set to "raw", prints space-separated, quoted key=value pairs
           (machine readable).

           If set to "col:", prints only the <columns> specified (comma-separated list). Header lines are
           ommitted if the "h:" modifier is present. Columns prefixed with "-" are collapsed if empty. Columns
           postfixed with ":RALIGN" are right-aligned.

       --pretty
           Print table output with lowercase, underlined column headings (instead of single-line uppercase
           headings).

       -S, --print-schedule
           Print detailed scheduler information on run, snapshot, resume, prune and archive commands. Use the
           --format command line option to switch between different output formats.

       --progress
           Show progress bar on send-receive operation. Requires "mbuffer" command (version >= 20180505)
           installed on the host running btrbk.

       --lockfile <file>
           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. Overrides configuration option
           "lockfile". Ignored on dryrun (-n, --dry-run).

       --override <config_option>=<value>
           Override a configuration option <config_option> with <value>. Globally, for ALL contexts. Use with
           care!

COMMANDS

Actions
The following commands are used to create snapshots and/or backups. All actions can operate in dry-run
mode (-n, --dry-run). Use the --format command line option to switch between different output formats.

See section RETENTION POLICY in btrbk.conf(5) for information on configuring the retention policy.

run [filter...]
Perform snapshot and backup operations as specified in the configuration file. If the optional
[filter...] arguments are present, snapshots and backups are only performed for the
subvolumes/targets matching a filter statement (see FILTER STATEMENTS below).

Step 0: Read Data
Read information from the source and target btrfs filesystems in order to perform sanity checks
and identify parent/child and received-from relationships.

Step 1: Create Snapshots
If the checks succeed, btrbk creates snapshots for the source subvolumes specified in the
configuration file, according to the snapshot_create option.

Step 2: Create Backups
For each specified target, btrbk creates the backups as follows: After comparing the backups to
the source snapshots, btrbk transfers all missing snapshots needed to satisfy the configured
target retention policy, incrementally from the latest common parent subvolume found. If no
common parent subvolume is found (or if the incremental option is set to “no”), a full
(non-incremental) backup is created.

Step 3: Delete Backups
Unless the -p, --preserve or --preserve-backups option is set, backup subvolumes that are not
preserved by their configured retention policy will be deleted. Note that the latest
snapshot/backup pair are always preserved, regardless of the retention policy.

Step 4: Delete Snapshots
Unless the -p, --preserve or --preserve-snapshots option is set, snapshots that are not preserved
by their configured retention policy will be deleted. Note that the latest snapshot (the one
created in step 1) as well as the latest snapshot/backup pair are always preserved, regardless of
the retention policy. If any target is unreachable or has errors, all snapshots are preserved in
order not to break the incremental chain.

dryrun [filter...]
Don’t run any btrfs commands that would alter the filesystem, just show the snapshots and backup
subvolumes that would be created/deleted by the run command. Use in conjunction with -l debug to see
the btrfs commands that would be executed.

snapshot [filter...]
Snapshot only: skips backup creation and deletion (steps 2 and 3). Use in conjunction with -p,
--preserve (or --preserve-snapshots) if you also want to skip snapshot deletion (step 4).

Note that snapshot deletion is skipped if the target is not accessible, as it is still required in
order to determine the latest snapshot/backup pair (which is always preserved, regardless of the
retention policy).

resume [filter...]
Resume backups: skips snapshot creation (step 1), transfers and deletes snapshots/backups in order to
satisfy their configured retention policy. Use in conjunction with -p, --preserve,
--preserve-backups, --preserve-snapshots if you want to skip backup and/or snapshot deletion (steps
3, 4).

prune [filter...]
Prune snapshots and backups: skips snapshot and backup creation (steps 1, 2), only deletes snapshots
and backups in order to satisfy their configured retention policy. Useful for cleaning the disk after
changing the retention policy. Use in conjunction with --preserve-backups, --preserve-snapshots if
you want to skip backup or snapshot deletion (steps 3, 4).

Note that deletion is skipped if source or target is not accessible, as it is still required in order
to determine the latest snapshot/backup pair (which is always preserved, regardless of the retention
policy).

archive <source> <target> [--raw]
Recursively copy all subvolumes created by btrbk from <source> to <target> directory, optionally
rescheduled using archive_preserve_* configuration options. Also creates directory tree on <target>.
Useful for creating extra archive copies (clones) from your backup disks. Note that you can continue
using btrbk after swapping your backup disk with the archive disk.

If you want to use nested subvolumes on the target filesystem, you need to create them by hand (e.g.
by running "btrfs subvolume create <target>/dir"). Check the output of --dry-run if unsure.

Note that this feature needs a linux kernel >=4.4 to work correctly!

If --raw option is set, creates raw targets (experimental, see btrbk.conf(5), TARGET TYPES).

clean [filter...]
Delete incomplete (garbled) backups. Incomplete backups can be left behind on network errors or kill
signals while a send/receive operation is ongoing, and are identified by the "received_uuid" flag not
being set on a target (backup) subvolume.

The following table gives a quick overview of the action commands and resulting snapshot creation (S+),
backup creation (B+), snapshot deletion (S-), and backup deletion (B-):

Command Option S+ B+ S- B-
--------------------------------------------
run x x x x
run --preserve x x
run --preserve-snapshots x x x
run --preserve-backups x x x
snapshot x x
snapshot --preserve x
resume x x x
resume --preserve x
resume --preserve-snapshots x x
resume --preserve-backups x x
prune x x
prune --preserve-snapshots x
prune --preserve-backups x

Informative Commands
The following commands are informative only, and will not alter the file system.

stats [filter...]
Print statistics of snapshot and backup subvolumes. Optionally filtered by [filter...] arguments (see
FILTER STATEMENTS below).

list <subcommand> [filter...]
Print information defined by <subcommand> in a tabular form. Optionally filtered by [filter...]
arguments (see FILTER STATEMENTS below).

Available subcommands (default “all”):

all
List all snapshots and backups created by btrbk.

snapshots
List all snapshots created by btrbk.

backups
List all backups (and correlated snapshots) created by btrbk.

latest
List most recent common snapshot/backup pair, or most recent snapshot if no common found.

config
List configured source/snapshot/target relations.

source
List configured source/snapshot relations.

volume
List configured volume sections.

target
List configured targets.

Use the --format command line option to switch between different output formats.

usage [filter...]
Print filesystem usage information for all source/target volumes, optionally filtered by [filter...]
arguments (see FILTER STATEMENTS below). Note that the "free" value is an estimate of the amount of
data that can still be written to the file system.

origin <subvolume>
Print the subvolume origin tree: Shows the parent-child relationships as well as the received-from
information. Use the --format command line option to switch between different output formats.

diff <from> <to>
List the modified files since generation (transid) of subvolume <from> in subvolume <to>. Columns:

SIZE file was modified for a total of SIZE bytes
COUNT file was modified in COUNT generations
FLAGS "+" file accessed at offset 0 (at least once)
"c" COMPRESS flag is set (at least once)
"i" INLINE flag is set (at least once)

extents [diff] <subvolume>... [exclusive <subvolume>...]
Print accurate disk space usage and diff based on extent data (FIEMAP ioctl, slow!).

Subvolumes following the exclusive keyword are added to a separate set, and additional set-exclusive
data is printed at the end of the list. This gives a hint of how much data will be freed if deleting
all subvolumes in the set. Example:

btrbk extents diff /backup/data.* exclusive /backup/data.2010*

The EXCLUSIVE column shows the set-exclusive data of all other listed (!) subvolumes (relative
complement of block regions). Provided that all related subvolumes (holding references to extents)
are also listed, this amount of disk space would be freed when deleting the subvolume.

The DIFF column shows the data added to the previous subvolume (relative complement of block
regions).

If called with the --related option, btrbk also lists all related subvolumes. This is not recommended
for backups, as parent-uuid relations break for received subvolumes as soon as an intermediate
subvolume is deleted.

Note that reading all extents is a disk-intensive task, expect long execution times and high ram
usage. Consider setting cache_dir.

ls <path>|<url>...
List all btrfs subvolumes below <path>. Use the --format command line option to switch between
different output formats. See lsbtr(1).

config print|print-all
Prints the parsed configuration file.

FILTER STATEMENTS

       Filter arguments are accepted in form:

       <group-name>
           Matches the group configuration option of volume, subvolume or target sections.

       <hostname>[:<port>]
           Matches the hostname portion from <url> of volume or target sections.

       <directory>|<url>
           Matches volume, subvolume or target sections by either relative or absolute path (if starting with
           "/" or "ssh://" or "<hostname>:/"), accepting wildcard character "*". Relative paths are matched
           against the end of the pathname. Either:

           <volume-directory>
               Matches volume sections.

           <volume-directory>/<subvolume-name>
               Matches subvolume sections.

           <volume-directory>/<snapshot-dir>/<snapshot-name>
               Matches subvolume sections defining snapshots with the configured snapshot_dir and snapshot_name.

           <target-directory>
               Matches target sections.

           <target-directory>/<snapshot-name>
               Matches target sections within subvolume sections defining snapshots with the configured
               snapshot_name.

           Accepted formats for <url> are:

               ssh://<hostname>[:<port>]/<directory>
               <hostname>:<directory>

       Note that for run and snapshot commands, a filter matching a target configuration section also enables
       snapshot creation of the surrounding subvolume section. If this is not desired, consider running snapshot
       and resume commands separately.

       Filter statements can match multiple times (e.g. on group as well as host name). In such a case, all
       matches are processed.

FILES

       /etc/btrbk.conf, /etc/btrbk/btrbk.conf
           Default configuration file. The file format and configuration options are described in btrbk.conf(5).

EXIT STATUS

       btrbk returns the following error codes:

       0
           No problems occurred.

       1
           Generic error code.

       2
           Parse error: when parsing command-line options or configuration file.

       3
           Lockfile error: if lockfile is present on startup.

       10
           Backup abort: At least one backup task aborted.

       255
           Script error.

AVAILABILITY

       Please refer to the btrbk project page https://digint.ch/btrbk/ for further details.

AUTHOR

       Axel Burri axel@tty0.ch

Btrbk 0.32.6                                       2023-03-25                                           BTRBK(1)