bzfs

bzfs

• Introduction
• Periodic Jobs with bzfs_jobrunner
• Quickstart
• Installation
• Design Aspects
• Continuous Testing
• Unit Testing on GitHub
• Unit Testing Locally
• Man Page

Introduction

bzfs is a backup command line tool that reliably replicates ZFS snapshots from a (local or remote) source ZFS dataset (ZFS filesystem or ZFS volume) and its descendant datasets to a (local or remote) destination ZFS dataset to make the destination dataset a recursively synchronized copy of the source dataset, using zfs send/receive/rollback/destroy and ssh tunnel as directed. For example, bzfs can be used to incrementally replicate all ZFS snapshots since the most recent common snapshot from source to destination, in order to help protect against data loss or ransomware.

When run for the first time, bzfs replicates the dataset and all its snapshots from the source to the destination. On subsequent runs, bzfs transfers only the data that has changed since the previous run, i.e. it incrementally replicates to the destination all intermediate snapshots that have been created on the source since the last run. Source ZFS snapshots older than the most recent common snapshot found on the destination are auto-skipped.

Unless bzfs is explicitly told to create snapshots on the source, it treats the source as read-only, thus the source remains unmodified. With the --dryrun flag, bzfs also treats the destination as read-only. In normal operation, bzfs treats the destination as append-only. Optional CLI flags are available to delete destination snapshots and destination datasets as directed, for example to make the destination identical to the source if the two have somehow diverged in unforeseen ways. This easily enables (re)synchronizing the backup from the production state, as well as restoring the production state from backup.

In the spirit of rsync, bzfs supports a variety of powerful include/exclude filters that can be combined to select which datasets, snapshots and properties to create, replicate, delete or compare.

Typically, a cron job on the source host runs bzfs periodically to create new snapshots and prune outdated snapshots on the source, whereas another cron job on the destination host runs bzfs periodically to prune outdated destination snapshots. Yet another cron job runs bzfs periodically to replicate the recently created snapshots from the source to the destination. The frequency of these periodic activities is typically every N milliseconds, every second, minute, hour, day, week, month and/or year (or multiples thereof).

All bzfs functions including snapshot creation, replication, deletion, comparison, etc. happily work with any snapshots in any format, even created or managed by third party ZFS snapshot management tools, including manual zfs snapshot/destroy. All functions can also be used independently. That is, if you wish you can use bzfs just for creating snapshots, or just for replicating, or just for deleting/pruning, or just for comparing snapshot lists.

The source 'pushes to' the destination whereas the destination 'pulls from' the source. bzfs is installed and executed on the 'initiator' host which can be either the host that contains the source dataset (push mode), or the destination dataset (pull mode), or both datasets (local mode, no network required, no ssh required), or any third-party (even non-ZFS OSX) host as long as that host is able to SSH (via standard 'ssh' OpenSSH CLI) into both the source and destination host (pull-push mode). In pull-push mode the source 'zfs send's the data stream to the initiator which immediately pipes the stream (without storing anything locally) to the destination host that 'zfs receive's it. Pull-push mode means that bzfs need not be installed or executed on either source or destination host. Only the underlying 'zfs' CLI must be installed on both source and destination host. bzfs can run as root or non-root user, in the latter case via a) sudo or b) when granted corresponding ZFS permissions by administrators via 'zfs allow' delegation mechanism.

bzfs is written in Python and continously runs a wide set of unit tests and integration tests to ensure coverage and compatibility with old and new versions of ZFS on Linux, FreeBSD and Solaris, on all Python versions >= 3.8 (including latest stable which is currently python-3.13).

bzfs is a stand-alone program with zero required dependencies, consisting of a single file, akin to a stand-alone shell script or binary executable. It is designed to be able to run in restricted barebones server environments. No external Python packages are required; indeed no Python package management at all is required. You can just copy the file wherever you like, for example into /usr/local/bin or similar, and simply run it like any stand-alone shell script or binary executable.

bzfs automatically replicates the snapshots of multiple datasets in parallel for best performance. Similarly, it quickly deletes (or monitors or compares) snapshots of multiple datasets in parallel. Atomic snapshots can be created as frequently as every N milliseconds.

Optionally, bzfs applies bandwidth rate-limiting and progress monitoring (via 'pv' CLI) during 'zfs send/receive' data transfers. When run across the network, bzfs also transparently inserts lightweight data compression (via 'zstd -1' CLI) and efficient data buffering (via 'mbuffer' CLI) into the pipeline between network endpoints during 'zfs send/receive' network transfers. If one of these utilities is not installed this is auto-detected, and the operation continues reliably without the corresponding auxiliary feature.

Periodic Jobs with bzfs_jobrunner

The software also ships with the bzfs_jobrunner companion program, which is a convenience wrapper around bzfs that simplifies periodic ZFS snapshot creation, replication, and pruning, across source host and multiple destination hosts, using a single shared jobconfig script.

Quickstart

• Create adhoc atomic snapshots without a schedule:

$ bzfs tank1/foo/bar dummy --recursive --skip-replication --create-src-snapshots \
--create-src-snapshots-plan "{'test':{'':{'adhoc':1}}}"

$ zfs list -t snapshot tank1/foo/bar
tank1/foo/bar@test_2024-11-06_08:30:05_adhoc 

• Create periodic atomic snapshots on a schedule, every hour and every day, by launching this from a periodic cron job:

$ bzfs tank1/foo/bar dummy --recursive --skip-replication --create-src-snapshots \
--create-src-snapshots-plan "{'prod':{'us-west-1':{'hourly':36,'daily':31}}}"

$ zfs list -t snapshot tank1/foo/bar
tank1/foo/bar@prod_us-west-1_2024-11-06_08:30:05_daily
tank1/foo/bar@prod_us-west-1_2024-11-06_08:30:05_hourly 

Note: A periodic snapshot is created if it is due per the schedule indicated by its suffix (e.g. _daily or _hourly or _minutely or _2secondly or _100millisecondly), or if the --create-src-snapshots-even-if-not-due flag is specified, or if the most recent scheduled snapshot is somehow missing. In the latter case bzfs immediately creates a snapshot (named with the current time, not backdated to the missed time), and then resumes the original schedule. If the suffix is _adhoc or not a known period then a snapshot is considered non-periodic and is thus created immediately regardless of the creation time of any existing snapshot.

• Replication example in local mode (no network, no ssh), to replicate ZFS dataset tank1/foo/bar to tank2/boo/bar:

$ bzfs tank1/foo/bar tank2/boo/bar

$ zfs list -t snapshot tank1/foo/bar
tank1/foo/bar@prod_us-west-1_2024-11-06_08:30:05_daily
tank1/foo/bar@prod_us-west-1_2024-11-06_08:30:05_hourly

$ zfs list -t snapshot tank2/boo/bar
tank2/boo/bar@prod_us-west-1_2024-11-06_08:30:05_daily
tank2/boo/bar@prod_us-west-1_2024-11-06_08:30:05_hourly

• Same example in pull mode:

$ bzfs [e-mail]:tank1/foo/bar tank2/boo/bar

• Same example in push mode:

$ bzfs tank1/foo/bar [e-mail]:tank2/boo/bar

• Same example in pull-push mode:

$ bzfs root@host1:tank1/foo/bar root@host2:tank2/boo/bar

• Example in local mode (no network, no ssh) to recursively replicate ZFS dataset tank1/foo/bar and its descendant datasets to tank2/boo/bar:

$ bzfs tank1/foo/bar tank2/boo/bar --recursive

$ zfs list -t snapshot -r tank1/foo/bar
tank1/foo/bar@prod_us-west-1_2024-11-06_08:30:05_daily
tank1/foo/bar@prod_us-west-1_2024-11-06_08:30:05_hourly
tank1/foo/bar/baz@prod_us-west-1_2024-11-06_08:40:00_daily
tank1/foo/bar/baz@prod_us-west-1_2024-11-06_08:40:00_hourly

$ zfs list -t snapshot -r tank2/boo/bar
tank2/boo/bar@prod_us-west-1_2024-11-06_08:30:05_daily
tank2/boo/bar@prod_us-west-1_2024-11-06_08:30:05_hourly
tank2/boo/bar/baz@prod_us-west-1_2024-11-06_08:40:00_daily
tank2/boo/bar/baz@prod_us-west-1_2024-11-06_08:40:00_hourly

• Example that makes destination identical to source even if the two have drastically diverged:

$ bzfs tank1/foo/bar tank2/boo/bar --recursive --force --delete-dst-datasets \
--delete-dst-snapshots

• Replicate all daily snapshots created during the last 7 days, and at the same time ensure that the latest 7 daily snapshots (per dataset) are replicated regardless of creation time:

$ bzfs tank1/foo/bar tank2/boo/bar --recursive --include-snapshot-regex '.*_daily' \
--include-snapshot-times-and-ranks '7 days ago..anytime' 'latest 7'

Note: The example above compares the specified times against the standard ZFS 'creation' time property of the snapshots (which is a UTC Unix time in integer seconds), rather than against a timestamp that may be part of the snapshot name.

• Delete all daily snapshots older than 7 days, but ensure that the latest 7 daily snapshots (per dataset) are retained regardless of creation time:

$ bzfs dummy tank2/boo/bar --dryrun --recursive --skip-replication \
--delete-dst-snapshots --include-snapshot-regex '.*_daily' \
--include-snapshot-times-and-ranks notime 'all except latest 7' \
--include-snapshot-times-and-ranks 'anytime..7 days ago'

Note: This also prints how many GB of disk space in total would be freed if the command were to be run for real without the --dryrun flag.

• Delete all daily snapshots older than 7 days, but ensure that the latest 7 daily snapshots (per dataset) are retained regardless of creation time. Additionally, only delete a snapshot if no corresponding snapshot or bookmark exists in the source dataset (same as above except replace the 'dummy' source with 'tank1/foo/bar'):

$ bzfs tank1/foo/bar tank2/boo/bar --dryrun --recursive --skip-replication \
--delete-dst-snapshots --include-snapshot-regex '.*_daily' \
--include-snapshot-times-and-ranks notime 'all except latest 7' \
--include-snapshot-times-and-ranks '7 days ago..anytime'

• Delete all daily snapshots older than 7 days, but ensure that the latest 7 daily snapshots (per dataset) are retained regardless of creation time. Additionally, only delete a snapshot if no corresponding snapshot exists in the source dataset (same as above except append 'no-crosscheck'):

$ bzfs tank1/foo/bar tank2/boo/bar --dryrun --recursive --skip-replication \
--delete-dst-snapshots --include-snapshot-regex '.*_daily' \
--include-snapshot-times-and-ranks notime 'all except latest 7' \
--include-snapshot-times-and-ranks 'anytime..7 days ago' \
--delete-dst-snapshots-no-crosscheck

• Delete all daily bookmarks older than 90 days, but retain the latest 200 daily bookmarks (per dataset) regardless of creation time:

$ bzfs dummy tank1/foo/bar --dryrun --recursive --skip-replication \
--delete-dst-snapshots=bookmarks --include-snapshot-regex '.*_daily' \
--include-snapshot-times-and-ranks notime 'all except latest 200' \
--include-snapshot-times-and-ranks 'anytime..90 days ago'

• Delete all tmp datasets within tank2/boo/bar:

$ bzfs dummy tank2/boo/bar --dryrun --recursive --skip-replication \
--delete-dst-datasets --include-dataset-regex '(.*/)?tmp.*' --exclude-dataset-regex \
'!.*'

• Retain all secondly snapshots that were created less than 40 seconds ago, and ensure that the latest 40 secondly snapshots (per dataset) are retained regardless of creation time. Same for 40 minutely snapshots, 36 hourly snapshots, 31 daily snapshots, 12 weekly snapshots, 18 monthly snapshots, and 5 yearly snapshots:

$ bzfs dummy tank2/boo/bar --dryrun --recursive --skip-replication \
--delete-dst-snapshots --delete-dst-snapshots-except --include-snapshot-regex '.*_secondly' \
--include-snapshot-times-and-ranks '40 seconds ago..anytime' 'latest 40' \
--new-snapshot-filter-group --include-snapshot-regex '.*_minutely' \
--include-snapshot-times-and-ranks '40 minutes ago..anytime' 'latest 40' \
--new-snapshot-filter-group --include-snapshot-regex '.*_hourly' \
--include-snapshot-times-and-ranks '36 hours ago..anytime' 'latest 36' \
--new-snapshot-filter-group --include-snapshot-regex '.*_daily' \
--include-snapshot-times-and-ranks '31 days ago..anytime' 'latest 31' \
--new-snapshot-filter-group --include-snapshot-regex '.*_weekly' \
--include-snapshot-times-and-ranks '12 weeks ago..anytime' 'latest 12' \
--new-snapshot-filter-group --include-snapshot-regex '.*_monthly' \
--include-snapshot-times-and-ranks '18 months ago..anytime' 'latest 18' \
--new-snapshot-filter-group --include-snapshot-regex '.*_yearly' \
--include-snapshot-times-and-ranks '5 years ago..anytime' 'latest 5'

For convenience, the lengthy command line above can be expressed in a more concise way, like so:

$ bzfs dummy tank2/boo/bar --dryrun --recursive --skip-replication \
--delete-dst-snapshots --delete-dst-snapshots-except-plan \
"{'prod':{'onsite':{'secondly':40,'minutely':40,'hourly':36,'daily':31,'weekly':12,'monthly':18,'yearly':5}}}"

• Compare source and destination dataset trees recursively, for example to check if all recently taken snapshots have been successfully replicated by a periodic job. List snapshots only contained in src (tagged with 'src'), only contained in dst (tagged with 'dst'), and contained in both src and dst (tagged with 'all'), restricted to hourly and daily snapshots taken within the last 7 days, excluding the last 4 hours (to allow for some slack/stragglers), excluding temporary datasets:

$ bzfs tank1/foo/bar tank2/boo/bar --skip-replication \
--compare-snapshot-lists=src+dst+all --recursive --include-snapshot-regex \
'.*_(hourly|daily)' --include-snapshot-times-and-ranks '7 days ago..4 hours ago' \
--exclude-dataset-regex '(.*/)?tmp.*'

If the resulting TSV output file contains zero lines starting with the prefix 'src' and zero lines starting with the prefix 'dst' then no source snapshots are missing on the destination, and no destination snapshots are missing on the source, indicating that the periodic replication and pruning jobs perform as expected. The TSV output is sorted by dataset, and by ZFS creation time within each dataset - the first and last line prefixed with 'all' contains the metadata of the oldest and latest common snapshot, respectively. The --compare-snapshot-lists option also directly logs various summary stats, such as the metadata of the latest common snapshot, latest snapshots and oldest snapshots, as well as the time diff between the latest common snapshot and latest snapshot only in src (and only in dst), as well as how many src snapshots and how many GB of data are missing on dst, etc.

• Example with further options:

$ bzfs tank1/foo/bar [e-mail]:tank2/boo/bar --recursive \
--exclude-snapshot-regex '.*_(secondly|minutely)' --exclude-snapshot-regex 'test_.*' \
--include-snapshot-times-and-ranks '7 days ago..anytime' 'latest 7' --exclude-dataset \
/tank1/foo/bar/temporary --exclude-dataset /tank1/foo/bar/baz/trash --exclude-dataset-regex \
'(.*/)?private' --exclude-dataset-regex '(.*/)?[Tt][Ee]?[Mm][Pp][-_]?[0-9]*' \
--ssh-dst-private-key /root/.ssh/id_rsa

Installation

# Ubuntu / Debian:
sudo apt-get -y install zfsutils-linux python3  # ensure zfs and python are installed
sudo apt-get -y install zstd pv mbuffer  # auxiliary helpers are optional

git clone https://github.com/whoschek/bzfs.git
cd bzfs/bzfs
./bzfs --help  # Run the CLI
./bzfs_jobrunner --help
sudo cp bzfs bzfs_jobrunner /usr/local/bin/  # Optional system installation

# Alternatively, install a release via pip:
pip install bzfs
bzfs --help  # Run the CLI
bzfs_jobrunner --help

Design Aspects

• Rsync'ish look and feel.
• Supports a variety of powerful include/exclude filters that can be combined to select which datasets, snapshots and properties to create or replicate or delete or compare.
• Supports pull, push, pull-push and local transfer mode.
• Prioritizes safe, reliable and predictable operations. Clearly separates read-only mode, append-only mode and delete mode.
• Continously tested on Linux, FreeBSD and Solaris.
• Code is almost 100% covered by tests.
• Automatically replicates the snapshots of multiple datasets in parallel for best performance. Similarly, quickly deletes (or monitors or compares) snapshots of multiple datasets in parallel. Atomic snapshots can be created as frequently as every N milliseconds.
• For replication, periodically prints progress bar, throughput metrics, ETA, etc, to the same console status line (but not to the log file), which is helpful if the program runs in an interactive terminal session. The metrics represent aggregates over the parallel replication tasks. Example console status line:

2025-01-17 01:23:04 [I] zfs sent 41.7 GiB 0:00:46 [963 MiB/s] [907 MiB/s] 80% ETA 0:00:04 ETA 01:23:08

• Simple and straightforward: Can be installed in less than a minute. Can be fully scripted without configuration files, or scheduled via cron or similar. Does not require a daemon other than ubiquitous sshd.
• Stays true to the ZFS send/receive spirit. Retains the ability to use ZFS CLI options for fine tuning. Does not attempt to "abstract away" ZFS concepts and semantics. Keeps simple things simple, and makes complex things possible.
• All ZFS and SSH commands (even in --dryrun mode) are logged such that they can be inspected, copy-and-pasted into a terminal/shell, and run manually to help anticipate or diagnose issues.
• Supports snapshotting, replicating (or deleting) dataset subsets via powerful include/exclude regexes and other filters, which can be combined into a mini filter pipeline. For example, can snapshot, replicate (or delete) all except temporary datasets and private datasets. Can be told to do such deletions only if a corresponding source dataset does not exist.
• Supports replicating (or deleting) snapshot subsets via powerful include/exclude regexes, time based filters, and oldest N/latest N filters, which can also be combined into a mini filter pipeline.
  • For example, can replicate (or delete) daily and weekly snapshots while ignoring hourly and 5 minute snapshots. Or, can replicate daily and weekly snapshots to a remote destination while replicating hourly and 5 minute snapshots to a local destination.
  • For example, can replicate (or delete) all daily snapshots older (or newer) than 90 days, and all weekly snapshots older (or newer) than 12 weeks.
  • For example, can replicate (or delete) all daily snapshots except the latest (or oldest) 90 daily snapshots, and all weekly snapshots except the latest (or oldest) 12 weekly snapshots.
  • For example, can replicate all daily snapshots that were created during the last 7 days, and at the same time ensure that at least the latest 7 daily snapshots are replicated regardless of creation time. This helps to safely cope with irregular scenarios where no snapshots were created or received within the last 7 days, or where more than 7 daily snapshots were created or received within the last 7 days.
  • For example, can delete all daily snapshots older than 7 days, but retain the latest 7 daily snapshots regardless of creation time. It can help to avoid accidental pruning of the last snapshot that source and destination have in common.
  • Can be told to do such deletions only if a corresponding snapshot does not exist in the source dataset.
  • Optionally, deletions can specify which snapshots to retain instead of which snapshots to delete.
  • Prints how many GB of disk space in total would be freed if the delete command were to be run for real without the --dryrun flag.
• Compare source and destination dataset trees recursively, in combination with snapshot filters and dataset filters.
• Also supports replicating arbitrary dataset tree subsets by feeding it a list of flat datasets.
• Efficiently supports complex replication policies with multiple sources and multiple destinations for each source.
• Can be told what ZFS dataset properties to copy, also via include/exclude regexes.
• Full and precise ZFS bookmark support for additional safety, or to reclaim disk space earlier.
• Can be strict or told to be tolerant of runtime errors.
• Automatically resumes ZFS send/receive operations that have been interrupted by network hiccups or other intermittent failures, via efficient 'zfs receive -s' and 'zfs send -t'.
• Similarly, can be told to automatically retry snapshot delete operations.
• Parametrizable retry logic.
• Multiple bzfs processes can run in parallel. If multiple processes attempt to write to the same destination dataset simultaneously this is detected and the operation can be auto-retried safely.
• A job that runs periodically declines to start if the same previous periodic job is still running without completion yet.
• Can log to local and remote destinations out of the box. Logging mechanism is customizable and plugable for smooth integration.
• Codebase is easy to change and maintain. No hidden magic. Python is very readable to contemporary engineers. Chances are that CI tests will catch changes that have unintended side effects.
• It's fast!

Continuous Testing

Results of continuous test runs on a matrix of various old and new versions of ZFS/Python/Linux/FreeBSD/Solaris are here, as generated by this script. The script also demonstrates functioning installation steps on Ubuntu, FreeBSD, Solaris, etc. The script also generates code coverage reports which are published here.

The gist is that it should work on any flavor, with python (3.8 or higher, no additional python packages required) only needed on the initiator host.

Unit Testing on GitHub

• First, on the GitHub page of this repo, click on "Fork/Create a new fork".
• Click the 'Actions' menu on your repo, and then enable GitHub Actions on your fork.
• Then select 'All workflows' -> 'Tests' on the left side.
• Then click the 'Run workflow' dropdown menu on the right side, which looks something like this screenshot.
• Select the name of the job to run (e.g. 'test_ubuntu_24_04' or 'test_freebsd_14_1' or 'test_solaris_11_4', etc) or select 'Run all jobs' to test all supported platforms, plus select the git branch to run with (typically the branch containing your changes).
• Then click the 'Run workflow' button which kicks off the job.
• Click on the job to watch job progress.
• Once the run completes, you can click on the wheel on the top right to select 'Download log archive', which is a zip file containing the output of all jobs of the run. This is useful for debugging.
• Once the job completes, also a coverage report appears on the bottom of the run page, which you can download by clicking on it. Unzip and browse the HTML coverage report to see if the code you added or changed is actually executed by a test. Experience shows that code that isn't executed likely contains bugs, so all changes (code lines and branch conditions) should be covered by a test before a merge is considered. In practice, this means to watch out for coverage report lines that aren't colored green.
• FYI, example test runs with coverage reports are here. Click on any run and browse to the bottom of the resulting run page to find the coverage reports, including a combined coverage report that merges all jobs of the run.

Unit Testing Locally

# verify zfs is installed
zfs --version

# verify python 3.8 or higher is installed
python3 --version

# verify sudo is working
sudo ls

# set this for unit tests if sshd is on a non-standard port (default is 22)
# export bzfs_test_ssh_port=12345
# export bzfs_test_ssh_port=22

# verify user can ssh in passwordless via loopback interface and private key;
# you should not be asked for a password
ssh -p $bzfs_test_ssh_port 127.0.0.1 echo hello

# verify zfs is on PATH
ssh -p $bzfs_test_ssh_port 127.0.0.1 zfs --version

# verify zpool is on PATH
ssh -p $bzfs_test_ssh_port 127.0.0.1 zpool --version

# verify zstd is on PATH for compression to become enabled
ssh -p $bzfs_test_ssh_port 127.0.0.1 zstd --version

# verify pv is on PATH for progress monitoring to become enabled
ssh -p $bzfs_test_ssh_port 127.0.0.1 pv --version

# verify mbuffer is on PATH for efficient buffering to become enabled
ssh -p $bzfs_test_ssh_port 127.0.0.1 mbuffer --version

# Finally, run unit tests. If cloned from git:
./test.sh

# Finally, run unit tests. If installed via 'pip install':
bzfs-test

Man Page

usage: bzfs [-h] [--recursive]
            [--include-dataset DATASET [DATASET ...]]
            [--exclude-dataset DATASET [DATASET ...]]
            [--include-dataset-regex REGEX [REGEX ...]]
            [--exclude-dataset-regex REGEX [REGEX ...]]
            [--exclude-dataset-property STRING]
            [--include-snapshot-regex REGEX [REGEX ...]]
            [--exclude-snapshot-regex REGEX [REGEX ...]]
            [--include-snapshot-times-and-ranks TIMERANGE [RANKRANGE ...]]
            [--include-snapshot-plan DICT_STRING]
            [--new-snapshot-filter-group] [--create-src-snapshots]
            [--create-src-snapshots-plan DICT_STRING]
            [--create-src-snapshots-timeformat STRFTIME_SPEC]
            [--create-src-snapshots-timezone TZ_SPEC]
            [--create-src-snapshots-even-if-not-due]
            [--create-src-snapshots-enable-snapshots-changed-cache]
            [--zfs-send-program-opts STRING]
            [--zfs-recv-program-opts STRING]
            [--zfs-recv-program-opt STRING]
            [--force-rollback-to-latest-snapshot]
            [--force-rollback-to-latest-common-snapshot] [--force]
            [--force-destroy-dependents] [--force-unmount]
            [--force-once] [--skip-parent]
            [--skip-missing-snapshots [{fail,dataset,continue}]]
            [--retries INT] [--retry-min-sleep-secs FLOAT]
            [--retry-max-sleep-secs FLOAT]
            [--retry-max-elapsed-secs FLOAT]
            [--skip-on-error {fail,tree,dataset}] [--skip-replication]
            [--delete-dst-datasets]
            [--delete-dst-snapshots [{snapshots,bookmarks}]]
            [--delete-dst-snapshots-no-crosscheck]
            [--delete-dst-snapshots-except]
            [--delete-dst-snapshots-except-plan DICT_STRING]
            [--delete-empty-dst-datasets [{snapshots,snapshots+bookmarks}]]
            [--monitor-snapshots DICT_STRING]
            [--monitor-snapshots-dont-warn]
            [--monitor-snapshots-dont-crit]
            [--compare-snapshot-lists [{src,dst,all,src+dst,src+all,dst+all,src+dst+all}]]
            [--dryrun [{recv,send}]] [--verbose] [--quiet]
            [--no-privilege-elevation] [--no-stream]
            [--no-resume-recv] [--no-create-bookmark]
            [--no-use-bookmark] [--ssh-cipher STRING]
            [--ssh-src-private-key FILE] [--ssh-dst-private-key FILE]
            [--ssh-src-user STRING] [--ssh-dst-user STRING]
            [--ssh-src-host STRING] [--ssh-dst-host STRING]
            [--ssh-src-port INT] [--ssh-dst-port INT]
            [--ssh-src-extra-opts STRING] [--ssh-src-extra-opt STRING]
            [--ssh-dst-extra-opts STRING] [--ssh-dst-extra-opt STRING]
            [--ssh-src-config-file FILE] [--ssh-dst-config-file FILE]
            [--threads INT[%]]
            [--max-concurrent-ssh-sessions-per-tcp-connection INT]
            [--bwlimit STRING] [--compression-program STRING]
            [--compression-program-opts STRING]
            [--mbuffer-program STRING] [--mbuffer-program-opts STRING]
            [--ps-program STRING] [--pv-program STRING]
            [--pv-program-opts STRING] [--shell-program STRING]
            [--ssh-program STRING] [--sudo-program STRING]
            [--zfs-program STRING] [--zpool-program STRING]
            [--log-dir DIR] [--log-file-prefix STRING]
            [--log-file-infix STRING] [--log-file-suffix STRING]
            [--log-subdir {daily,hourly,minutely}]
            [--log-syslog-address STRING]
            [--log-syslog-socktype {UDP,TCP}]
            [--log-syslog-facility INT] [--log-syslog-prefix STRING]
            [--log-syslog-level {CRITICAL,ERROR,WARN,INFO,DEBUG,TRACE}]
            [--log-config-file STRING]
            [--log-config-var NAME:VALUE [NAME:VALUE ...]]
            [--include-envvar-regex REGEX [REGEX ...]]
            [--exclude-envvar-regex REGEX [REGEX ...]]
            [--yearly_month INT] [--yearly_monthday INT]
            [--yearly_hour INT] [--yearly_minute INT]
            [--yearly_second INT] [--monthly_monthday INT]
            [--monthly_hour INT] [--monthly_minute INT]
            [--monthly_second INT] [--weekly_weekday INT]
            [--weekly_hour INT] [--weekly_minute INT]
            [--weekly_second INT] [--daily_hour INT]
            [--daily_minute INT] [--daily_second INT]
            [--hourly_minute INT] [--hourly_second INT]
            [--minutely_second INT] [--secondly_millisecond INT]
            [--millisecondly_microsecond INT]
            [--zfs-recv-o-targets {full,incremental,full+incremental}]
            [--zfs-recv-o-sources STRING]
            [--zfs-recv-o-include-regex REGEX [REGEX ...]]
            [--zfs-recv-o-exclude-regex REGEX [REGEX ...]]
            [--zfs-recv-x-targets {full,incremental,full+incremental}]
            [--zfs-recv-x-sources STRING]
            [--zfs-recv-x-include-regex REGEX [REGEX ...]]
            [--zfs-recv-x-exclude-regex REGEX [REGEX ...]] [--version]
            [--help, -h]
            SRC_DATASET DST_DATASET [SRC_DATASET DST_DATASET ...]

SRC_DATASET DST_DATASET

• SRC_DATASET: Source ZFS dataset (and its descendants) that will be replicated. Can be a ZFS filesystem or ZFS volume. Format is [[user@]host:]dataset. The host name can also be an IPv4 address (or an IPv6 address where each ':' colon character must be replaced with a '|' pipe character for disambiguation). If the host name is '-', the dataset will be on the local host, and the corresponding SSH leg will be omitted. The same is true if the host is omitted and the dataset does not contain a ':' colon at the same time. Local dataset examples: tank1/foo/bar, tank1, -:tank1/foo/bar:baz:boo Remote dataset examples: host:tank1/foo/bar, host.example.com:tank1/foo/bar, root@host:tank, [e-mail]:tank1/foo/bar, user@127.0.0.1:tank1/foo/bar:baz:boo, user@||1:tank1/foo/bar:baz:boo. The first component of the ZFS dataset name is the ZFS pool name, here tank1. If the option starts with a + prefix then dataset names are read from the UTF-8 text file given after the + prefix, with each line in the file containing a SRC_DATASET and a DST_DATASET, separated by a tab character. Example: +root_dataset_names.txt, +/path/to/root_dataset_names.txt

  DST_DATASET: Destination ZFS dataset for replication and deletion. Has same naming format as SRC_DATASET. During replication, destination datasets that do not yet exist are created as necessary, along with their parent and ancestors.

  Performance Note: bzfs automatically replicates multiple datasets in parallel. It replicates snapshots in parallel across datasets and serially within a dataset. All child datasets of a dataset may be processed in parallel. For consistency, processing of a dataset only starts after processing of all its ancestor datasets has completed. Further, when a thread is ready to start processing another dataset, it chooses the next dataset wrt. case-sensitive sort order from the datasets that are currently available for start of processing. Initially, only the roots of the selected dataset subtrees are available for start of processing. The degree of parallelism is configurable with the --threads option (see below).

--recursive, -r

• During snapshot creation, replication, deletion and comparison, also consider descendant datasets, i.e. datasets within the dataset tree, including children, and children of children, etc.

--include-dataset DATASET [DATASET ...]

• During snapshot creation, replication, deletion and comparison, select any ZFS dataset (and its descendants) that is contained within SRC_DATASET (DST_DATASET in case of deletion) if its dataset name is one of the given include dataset names but none of the exclude dataset names. If a dataset is excluded its descendants are automatically excluded too, and this decision is never reconsidered even for the descendants because exclude takes precedence over include.

  A dataset name is absolute if the specified dataset is prefixed by /, e.g. /tank/baz/tmp. Otherwise the dataset name is relative wrt. source and destination, e.g. baz/tmp if the source is tank.

  This option is automatically translated to an --include-dataset-regex (see below) and can be specified multiple times.

  If the option starts with a + prefix then dataset names are read from the newline-separated UTF-8 text file given after the + prefix, one dataset per line inside of the text file.

  Examples: /tank/baz/tmp (absolute), baz/tmp (relative), +dataset_names.txt, +/path/to/dataset_names.txt

--exclude-dataset DATASET [DATASET ...]

• Same syntax as --include-dataset (see above) except that the option is automatically translated to an --exclude-dataset-regex (see below).

--include-dataset-regex REGEX [REGEX ...]

• During snapshot creation, replication (and deletion) and comparison, select any ZFS dataset (and its descendants) that is contained within SRC_DATASET (DST_DATASET in case of deletion) if its relative dataset path (e.g. baz/tmp) wrt. SRC_DATASET (DST_DATASET in case of deletion) matches at least one of the given include regular expressions but none of the exclude regular expressions. If a dataset is excluded its descendants are automatically excluded too, and this decision is never reconsidered even for the descendants because exclude takes precedence over include.

  This option can be specified multiple times. A leading ! character indicates logical negation, i.e. the regex matches if the regex with the leading ! character removed does not match.

  If the option starts with a + prefix then regex names are read from the newline-separated UTF-8 text file given after the + prefix, one regex per line inside of the text file.

  Default: .* (include all datasets).

  Examples: baz/tmp, (.*/)?doc[^/]*/(private|confidential).*, !public, +dataset_regexes.txt, +/path/to/dataset_regexes.txt

--exclude-dataset-regex REGEX [REGEX ...]

• Same syntax as --include-dataset-regex (see above) except that the default is (.*/)?[Tt][Ee]?[Mm][Pp][-_]?[0-9]* (exclude tmp datasets). Example: !.* (exclude no dataset)

--exclude-dataset-property STRING

• The name of a ZFS dataset user property (optional). If this option is specified, the effective value (potentially inherited) of that user property is read via 'zfs list' for each selected source dataset to determine whether the dataset will be included or excluded, as follows:

  a) Value is 'true' or '-' or empty string or the property is missing: Include the dataset.

  b) Value is 'false': Exclude the dataset and its descendants.

  c) Value is a comma-separated list of host names (no spaces, for example: 'store001,store002'): Include the dataset if the host name of the host executing bzfs is contained in the list, otherwise exclude the dataset and its descendants.

  If a dataset is excluded its descendants are automatically excluded too, and the property values of the descendants are ignored because exclude takes precedence over include.

  Examples: 'syncoid:sync', 'com.example.eng.project.x:backup'

  Note: The use of --exclude-dataset-property is discouraged for most use cases. It is more flexible, more powerful, and more efficient to instead use a combination of --include/exclude-dataset-regex and/or --include/exclude-dataset to achieve the same or better outcome.

--include-snapshot-regex REGEX [REGEX ...]

• During replication, deletion and comparison, select any source ZFS snapshot that has a name (i.e. the part after the '@') that matches at least one of the given include regular expressions but none of the exclude regular expressions. If a snapshot is excluded this decision is never reconsidered because exclude takes precedence over include.

  This option can be specified multiple times. A leading ! character indicates logical negation, i.e. the regex matches if the regex with the leading ! character removed does not match.

  Default: .* (include all snapshots). Examples: test_.*, !prod_.*, .*_(hourly|frequent), !.*_(weekly|daily)

  Note: All --include/exclude-snapshot-* CLI option groups are combined into a mini filter pipeline. A filter pipeline is executed in the order given on the command line, left to right. For example if --include-snapshot-times-and-ranks (see below) is specified on the command line before --include/exclude-snapshot-regex, then --include-snapshot-times-and-ranks will be applied before --include/exclude-snapshot-regex. The pipeline results would not always be the same if the order were reversed. Order matters.

  Note: During replication, bookmarks are always retained aka selected in order to help find common snapshots between source and destination.

--exclude-snapshot-regex REGEX [REGEX ...]

• Same syntax as --include-snapshot-regex (see above) except that the default is to exclude no snapshots.

--include-snapshot-times-and-ranks TIMERANGE [RANKRANGE ...]

• This option takes as input parameters a time range filter and an optional rank range filter. It separately computes the results for each filter and selects the UNION of both results. To instead use a pure rank range filter (no UNION), or a pure time range filter (no UNION), simply use 'notime' aka '0..0' to indicate an empty time range, or omit the rank range, respectively. This option can be specified multiple times.

  Replication Example (UNION):

  Specify to replicate all daily snapshots created during the last 7 days, and at the same time ensure that the latest 7 daily snapshots (per dataset) are replicated regardless of creation time, like so: --include-snapshot-regex '.*_daily' --include-snapshot-times-and-ranks '7 days ago..anytime' 'latest 7'

  Deletion Example (no UNION):

  Specify to delete all daily snapshots older than 7 days, but ensure that the latest 7 daily snapshots (per dataset) are retained regardless of creation time, like so: --include-snapshot-regex '.*_daily' --include-snapshot-times-and-ranks notime 'all except latest 7' --include-snapshot-times-and-ranks 'anytime..7 days ago'

  This helps to safely cope with irregular scenarios where no snapshots were created or received within the last 7 days, or where more than 7 daily snapshots were created within the last 7 days. It can also help to avoid accidental pruning of the last snapshot that source and destination have in common.

  TIMERANGE:

  The ZFS 'creation' time of a snapshot (and bookmark) must fall into this time range in order for the snapshot to be included. The time range consists of a 'start' time, followed by a '..' separator, followed by an 'end' time. For example '2024-01-01..2024-04-01', or 'anytime..anytime' aka *..* aka all times, or 'notime' aka '0..0' aka empty time range. Only snapshots (and bookmarks) in the half-open time range [start, end) are included; other snapshots (and bookmarks) are excluded. If a snapshot is excluded this decision is never reconsidered because exclude takes precedence over include. Each of the two specified times can take any of the following forms:

  • a) anytime aka * wildcard; represents negative or positive infinity.

  • b) a non-negative integer representing a UTC Unix time in seconds. Example: 1728109805

  • c) an ISO 8601 datetime string with or without timezone. Examples: '2024-10-05', '2024-10-05T14:48:55', '2024-10-05T14:48:55+02', '2024-10-05T14:48:55-04:30'. If the datetime string does not contain time zone info then it is assumed to be in the local time zone. Timezone string support requires Python >= 3.11.

  • d) a duration that indicates how long ago from the current time, using the following syntax: a non-negative integer, followed by an optional space, followed by a duration unit that is one of 'seconds', 'secs', 'minutes', 'mins', 'hours', 'days', 'weeks', 'months', 'years', followed by an optional space, followed by the word 'ago'. Examples: '0secs ago', '40 mins ago', '36hours ago', '90days ago', '12weeksago'.

  • Note: This option compares the specified time against the standard ZFS 'creation' time property of the snapshot (which is a UTC Unix time in integer seconds), rather than against a timestamp that may be part of the snapshot name. You can list the ZFS creation time of snapshots and bookmarks as follows: zfs list -t snapshot,bookmark -o name,creation -s creation -d 1 $SRC_DATASET (optionally add the -p flag to display UTC Unix time in integer seconds).

  Note: During replication, bookmarks are always retained aka selected in order to help find common snapshots between source and destination.

  RANKRANGE:

  Specifies to include the N (or N%) oldest snapshots or latest snapshots, and exclude all other snapshots (default: include no snapshots). Snapshots are sorted by creation time (actually, by the 'createtxg' ZFS property, which serves the same purpose but is more precise). The rank position of a snapshot is the zero-based integer position of the snapshot within that sorted list. A rank consists of the optional words 'all except' (followed by an optional space), followed by the word 'oldest' or 'latest', followed by a non-negative integer, followed by an optional '%' percent sign. A rank range consists of a lower rank, followed by a '..' separator, followed by a higher rank. If the optional lower rank is missing it is assumed to be 0. Examples:

  • 'oldest 10%' aka 'oldest 0..oldest 10%' (include the oldest 10% of all snapshots)

  • 'latest 10%' aka 'latest 0..latest 10%' (include the latest 10% of all snapshots)

  • 'all except latest 10%' aka 'oldest 90%' aka 'oldest 0..oldest 90%' (include all snapshots except the latest 10% of all snapshots)

  • 'oldest 90' aka 'oldest 0..oldest 90' (include the oldest 90 snapshots)

  • 'latest 90' aka 'latest 0..latest 90' (include the latest 90 snapshots)

  • 'all except oldest 90' aka 'oldest 90..oldest 100%' (include all snapshots except the oldest 90 snapshots)

  • 'all except latest 90' aka 'latest 90..latest 100%' (include all snapshots except the latest 90 snapshots)

  • 'latest 1' aka 'latest 0..latest 1' (include the latest snapshot)

  • 'all except latest 1' aka 'latest 1..latest 100%' (include all snapshots except the latest snapshot)

  • 'oldest 2' aka 'oldest 0..oldest 2' (include the oldest 2 snapshots)

  • 'all except oldest 2' aka 'oldest 2..oldest 100%' (include all snapshots except the oldest 2 snapshots)

  • 'oldest 100%' aka 'oldest 0..oldest 100%' (include all snapshots)

  • 'oldest 0%' aka 'oldest 0..oldest 0%' (include no snapshots)

  • 'oldest 0' aka 'oldest 0..oldest 0' (include no snapshots)

  Note: Percentage calculations are not based on the number of snapshots contained in the dataset on disk, but rather based on the number of snapshots arriving at the filter. For example, if only two daily snapshots arrive at the filter because a prior filter excludes hourly snapshots, then 'latest 10' will only include these two daily snapshots, and 'latest 50%' will only include one of these two daily snapshots.

  Note: During replication, bookmarks are always retained aka selected in order to help find common snapshots between source and destination. Bookmarks do not count towards N or N% wrt. rank.

  Note: If a snapshot is excluded this decision is never reconsidered because exclude takes precedence over include.

--include-snapshot-plan DICT_STRING

• Replication periods to be used if replicating snapshots within the selected destination datasets. Has the same format as --create-src-snapshots-plan and --delete-dst-snapshots-except-plan (see below). Snapshots that do not match a period will not be replicated. To avoid unexpected surprises, make sure to carefully specify ALL snapshot names and periods that shall be replicated, in combination with --dryrun.

  Example: "{'prod': {'onsite': {'secondly': 40, 'minutely': 40, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}, 'us-west-1': {'secondly': 0, 'minutely': 0, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}, 'eu-west-1': {'secondly': 0, 'minutely': 0, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}}, 'test': {'offsite': {'12hourly': 42, 'weekly': 12}, 'onsite': {'100millisecondly': 42}}}". This example will, for the organization 'prod' and the intended logical target 'onsite', replicate secondly snapshots that were created less than 40 seconds ago, yet replicate the latest 40 secondly snapshots regardless of creation time. Analog for the latest 40 minutely snapshots, latest 36 hourly snapshots, etc. Note: A zero within a period (e.g. 'hourly': 0) indicates that no snapshots shall be replicated for the given period.

  Note: --include-snapshot-plan is a convenience option that auto-generates a series of the following other options: --new-snapshot-filter-group, --include-snapshot-regex, --include-snapshot-times-and-ranks

--new-snapshot-filter-group

• Starts a new snapshot filter group containing separate --{include|exclude}-snapshot-* filter options. The program separately computes the results for each filter group and selects the UNION of all results. This option can be specified multiple times and serves as a separator between groups. Example:

  Delete all minutely snapshots older than 40 minutes, but ensure that the latest 40 minutely snapshots (per dataset) are retained regardless of creation time. Additionally, delete all hourly snapshots older than 36 hours, but ensure that the latest 36 hourly snapshots (per dataset) are retained regardless of creation time. Additionally, delete all daily snapshots older than 31 days, but ensure that the latest 31 daily snapshots (per dataset) are retained regardless of creation time: bzfs dummy tank2/boo/bar --dryrun --recursive --skip-replication --delete-dst-snapshots --include-snapshot-regex '.*_minutely' --include-snapshot-times-and-ranks notime 'all except latest 40' --include-snapshot-times-and-ranks 'anytime..40 minutes ago' --new-snapshot-filter-group --include-snapshot-regex '.*_hourly' --include-snapshot-times-and-ranks notime 'all except latest 36' --include-snapshot-times-and-ranks 'anytime..36 hours ago' --new-snapshot-filter-group --include-snapshot-regex '.*_daily' --include-snapshot-times-and-ranks notime 'all except latest 31' --include-snapshot-times-and-ranks 'anytime..31 days ago'

--create-src-snapshots

• Do nothing if the --create-src-snapshots flag is missing. Otherwise, before the replication step (see below), atomically create new snapshots of the source datasets selected via --{include|exclude}-dataset* policy. The names of the snapshots can be configured via --create-src-snapshots-* suboptions (see below). To create snapshots only, without any other processing such as replication, etc, consider using this flag together with the --skip-replication flag.

  A periodic snapshot is created if it is due per the schedule indicated by --create-src-snapshots-plan (for example '_daily' or '_hourly' or _'10minutely' or '_2secondly' or '_100millisecondly'), or if the --create-src-snapshots-even-if-not-due flag is specified, or if the most recent scheduled snapshot is somehow missing. In the latter case bzfs immediately creates a snapshot (tagged with the current time, not backdated to the missed time), and then resumes the original schedule.

  If the snapshot suffix is '_adhoc' or not a known period then a snapshot is considered non-periodic and is thus created immediately regardless of the creation time of any existing snapshot.

  The implementation attempts to fit as many datasets as possible into a single (atomic) 'zfs snapshot' command line, using case-sensitive sort order, and using 'zfs snapshot -r' to the extent that this is compatible with the actual results of the schedule and the actual results of the --{include|exclude}-dataset* pruning policy. The snapshots of all datasets that fit within the same single 'zfs snapshot' CLI invocation will be taken within the same ZFS transaction group, and correspondingly have identical 'createtxg' ZFS property (but not necessarily identical 'creation' ZFS time property as ZFS actually provides no such guarantee), and thus be consistent. Dataset names that can't fit into a single command line are spread over multiple command line invocations, respecting the limits that the operating system places on the maximum length of a single command line, per getconf ARG_MAX.

  Note: All bzfs functions including snapshot creation, replication, deletion, comparison, etc. happily work with any snapshots in any format, even created or managed by third party ZFS snapshot management tools, including manual zfs snapshot/destroy.

--create-src-snapshots-plan DICT_STRING

• Creation periods that specify a schedule for when new snapshots shall be created on src within the selected datasets. Has the same format as --delete-dst-snapshots-except-plan.

  Example: "{'prod': {'onsite': {'secondly': 40, 'minutely': 40, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}, 'us-west-1': {'secondly': 0, 'minutely': 0, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}, 'eu-west-1': {'secondly': 0, 'minutely': 0, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}}, 'test': {'offsite': {'12hourly': 42, 'weekly': 12}, 'onsite': {'100millisecondly': 42}}}". This example will, for the organization 'prod' and the intended logical target 'onsite', create 'secondly' snapshots every second, 'minutely' snapshots every minute, hourly snapshots every hour, and so on. It will also create snapshots for the targets 'us-west-1' and 'eu-west-1' within the 'prod' organization. In addition, it will create snapshots every 12 hours and every week for the 'test' organization, and name them as being intended for the 'offsite' replication target. Analog for snapshots that are taken every 100 milliseconds within the 'test' organization.

  The example creates ZFS snapshots with names like prod_onsite_<timestamp>_secondly, prod_onsite_<timestamp>_minutely, prod_us-west-1_<timestamp>_hourly, prod_us-west-1_<timestamp>_daily, prod_eu-west-1_<timestamp>_hourly, prod_eu-west-1_<timestamp>_daily, test_offsite_<timestamp>_12hourly, test_offsite_<timestamp>_weekly, and so on.

  Note: A period name that is missing indicates that no snapshots shall be created for the given period.

  The period name can contain an optional positive integer immediately preceding the time period unit, for example _2secondly or _10minutely or _100millisecondly to indicate that snapshots are taken every 2 seconds, or every 10 minutes, or every 100 milliseconds, respectively.

--create-src-snapshots-timeformat STRFTIME_SPEC

• Default is %Y-%m-%d_%H:%M:%S. For the strftime format, see https://docs.python.org/3.11/library/datetime.html#strftime-strptime-behavior. Examples: %Y-%m-%d_%H:%M:%S.%f (adds microsecond resolution), %Y-%m-%d_%H:%M:%S%z (adds timezone offset), %Y-%m-%dT%H-%M-%S (no colons).

  The name of the snapshot created on the src is $org_$target_strftime(--create-src-snapshots-time*)_$period. Example: tank/foo@prod_us-west-1_2024-09-03_12:26:15_daily

--create-src-snapshots-timezone TZ_SPEC

• Default is the local timezone of the system running bzfs. When creating a new snapshot on the source, fetch the current time in the specified timezone, and feed that time, and the value of --create-src-snapshots-timeformat, into the standard strftime() function to generate the timestamp portion of the snapshot name. The TZ_SPEC input parameter is of the form 'UTC' or '+HHMM' or '-HHMM' for fixed UTC offsets, or an IANA TZ identifier for auto-adjustment to daylight savings time, or the empty string to use the local timezone, for example '', 'UTC', '+0000', '+0530', '-0400', 'America/Los_Angeles', 'Europe/Vienna'. For a list of valid IANA TZ identifiers see https://en.wikipedia.org/wiki/List_of_tz_database_time_zones#List

  To change the timezone not only for snapshot name creation, but in all respects for the entire program, use the standard 'TZ' Unix environment variable, like so: export TZ=UTC.

--create-src-snapshots-even-if-not-due

• Take snapshots immediately regardless of the creation time of any existing snapshot, even if snapshots are periodic and not actually due per the schedule.

--create-src-snapshots-enable-snapshots-changed-cache

• Maintain a local cache of recent snapshot creation times, running 'zfs list -t filesystem,volume -o snapshots_changed' instead of 'zfs list -t snapshot' to determine if a new snapshot shall be created on the src. This flag improves performance for high-frequency snapshotting use cases. Only relevant if --create-src-snapshots-even-if-not-due is not specified.

--zfs-send-program-opts STRING

• Parameters to fine-tune 'zfs send' behaviour (optional); will be passed into 'zfs send' CLI. The value is split on runs of one or more whitespace characters. Default is '--props --raw --compressed'. To run zfs send without options, specify the empty string: --zfs-send-program-opts=''. See https://openzfs.github.io/openzfs-docs/man/master/8/zfs-send.8.html and https://github.com/openzfs/zfs/issues/13024

--zfs-recv-program-opts STRING

• Parameters to fine-tune 'zfs receive' behaviour (optional); will be passed into 'zfs receive' CLI. The value is split on runs of one or more whitespace characters. Default is '-u'. To run zfs receive without options, specify the empty string: --zfs-recv-program-opts=''. Example: '-u -o canmount=noauto -o readonly=on -x keylocation -x keyformat -x encryption'. See https://openzfs.github.io/openzfs-docs/man/master/8/zfs-receive.8.html and https://openzfs.github.io/openzfs-docs/man/master/7/zfsprops.7.html

--zfs-recv-program-opt STRING

• Parameter to fine-tune 'zfs receive' behaviour (optional); will be passed into 'zfs receive' CLI. The value can contain spaces and is not split. This option can be specified multiple times. Example: --zfs-recv-program-opt=-o --zfs-recv-program-opt='org.zfsbootmenu:commandline=ro debug zswap.enabled=1'

--force-rollback-to-latest-snapshot

• Before replication, rollback the destination dataset to its most recent destination snapshot (if there is one), via 'zfs rollback', just in case the destination dataset was modified since its most recent snapshot. This is much less invasive than the other --force* options (see below).

--force-rollback-to-latest-common-snapshot

• Before replication, delete destination ZFS snapshots that are more recent than the most recent common snapshot selected on the source ('conflicting snapshots'), via 'zfs rollback'. Do no rollback if no common snapshot is selected.

--force

• Same as --force-rollback-to-latest-common-snapshot (see above), except that additionally, if no common snapshot is selected, then delete all destination snapshots before starting replication, and proceed without aborting. Without the --force* flags, the destination dataset is treated as append-only, hence no destination snapshot that already exists is deleted, and instead the operation is aborted with an error when encountering a conflicting snapshot.

  Analogy: --force-rollback-to-latest-snapshot is a tiny hammer, whereas --force-rollback-to-latest-common-snapshot is a medium sized hammer, --force is a large hammer, and --force-destroy-dependents is a very large hammer. Consider using the smallest hammer that can fix the problem. No hammer is ever used by default.

--force-destroy-dependents

• On destination, --force and --force-rollback-to-latest-common-snapshot and --delete-* will add the '-R' flag to their use of 'zfs rollback' and 'zfs destroy', causing them to delete dependents such as clones and bookmarks. This can be very destructive and is rarely advisable.

--force-unmount

• On destination, --force and --force-rollback-to-latest-common-snapshot will add the '-f' flag to their use of 'zfs rollback' and 'zfs destroy'.

--force-once, --f1

• Use the --force option or --force-rollback-to-latest-common-snapshot option at most once to resolve a conflict, then abort with an error on any subsequent conflict. This helps to interactively resolve conflicts, one conflict at a time.

--skip-parent

• During replication and deletion, skip processing of the SRC_DATASET and DST_DATASET and only process their descendant datasets, i.e. children, and children of children, etc (with --recursive). No dataset is processed unless --recursive is also specified. Analogy: bzfs --recursive --skip-parent src dst is akin to Unix cp -r src/* dst/ whereas bzfs --recursive --skip-parent --skip-replication --delete-dst-datasets dummy dst is akin to Unix rm -r dst/*

--skip-missing-snapshots [{fail,dataset,continue}]

• During replication, handle source datasets that select no snapshots (and no relevant bookmarks) as follows:

  a) 'fail': Abort with an error.

  b) 'dataset' (default): Skip the source dataset with a warning. Skip descendant datasets if --recursive and destination dataset does not exist. Otherwise skip to the next dataset.

  c) 'continue': Skip nothing. If destination snapshots exist, delete them (with --force) or abort with an error (without --force). If there is no such abort, continue processing with the next dataset. Eventually create empty destination dataset and ancestors if they do not yet exist and source dataset has at least one descendant that selects at least one snapshot.

--retries INT

• The maximum number of times a retryable replication or deletion step shall be retried if it fails, for example because of network hiccups (default: 2, min: 0). Also consider this option if a periodic pruning script may simultaneously delete a dataset or snapshot or bookmark while bzfs is running and attempting to access it.

--retry-min-sleep-secs FLOAT

• The minimum duration to sleep between retries (default: 0.125).

--retry-max-sleep-secs FLOAT

• The maximum duration to sleep between retries initially starts with --retry-min-sleep-secs (see above), and doubles on each retry, up to the final maximum of --retry-max-sleep-secs (default: 300). On each retry a random sleep time in the [--retry-min-sleep-secs, current max] range is picked. The timer resets after each operation.

--retry-max-elapsed-secs FLOAT

• A single operation (e.g. 'zfs send/receive' of the current dataset, or deletion of a list of snapshots within the current dataset) will not be retried (or not retried anymore) once this much time has elapsed since the initial start of the operation, including retries (default: 3600). The timer resets after each operation completes or retries exhaust, such that subsequently failing operations can again be retried.

--skip-on-error {fail,tree,dataset}

• During replication and deletion, if an error is not retryable, or --retries has been exhausted, or --skip-missing-snapshots raises an error, proceed as follows:

  a) 'fail': Abort the program with an error. This mode is ideal for testing, clear error reporting, and situations where consistency trumps availability.

  b) 'tree': Log the error, skip the dataset tree rooted at the dataset for which the error occurred, and continue processing the next (sibling) dataset tree. Example: Assume datasets tank/user1/foo and tank/user2/bar and an error occurs while processing tank/user1. In this case processing skips tank/user1/foo and proceeds with tank/user2.

  c) 'dataset' (default): Same as 'tree' except if the destination dataset already exists, skip to the next dataset instead. Example: Assume datasets tank/user1/foo and tank/user2/bar and an error occurs while processing tank/user1. In this case processing skips tank/user1 and proceeds with tank/user1/foo if the destination already contains tank/user1. Otherwise processing continues with tank/user2. This mode is for production use cases that require timely forward progress even in the presence of partial failures. For example, assume the job is to backup the home directories or virtual machines of thousands of users across an organization. Even if replication of some of the datasets for some users fails due too conflicts, busy datasets, etc, the replication job will continue for the remaining datasets and the remaining users.

--skip-replication

• Skip replication step (see above) and proceed to the optional --delete-dst-datasets step immediately (see below).

--delete-dst-datasets

• Do nothing if the --delete-dst-datasets option is missing. Otherwise, after successful replication step, if any, delete existing destination datasets that are selected via --{include|exclude}-dataset* policy yet do not exist within SRC_DATASET (which can be an empty dataset, such as the hardcoded virtual dataset named 'dummy'!). Do not recurse without --recursive. With --recursive, never delete non-selected dataset subtrees or their ancestors.

  For example, if the destination contains datasets h1,h2,h3,d1 whereas source only contains h3, and the include/exclude policy selects h1,h2,h3,d1, then delete datasets h1,h2,d1 on the destination to make it 'the same'. On the other hand, if the include/exclude policy only selects h1,h2,h3 then only delete datasets h1,h2 on the destination to make it 'the same'.

  Example to delete all tmp datasets within tank2/boo/bar: bzfs dummy tank2/boo/bar --dryrun --skip-replication --recursive --delete-dst-datasets --include-dataset-regex '(.*/)?tmp.*' --exclude-dataset-regex '!.*'

--delete-dst-snapshots [{snapshots,bookmarks}]

• Do nothing if the --delete-dst-snapshots option is missing. Otherwise, after successful replication, and successful --delete-dst-datasets step, if any, delete existing destination snapshots whose GUID does not exist within the source dataset (which can be an empty dummy dataset!) if the destination snapshots are selected by the --include/exclude-snapshot-* policy, and the destination dataset is selected via --{include|exclude}-dataset* policy. Does not recurse without --recursive.

  For example, if the destination dataset contains snapshots h1,h2,h3,d1 (h=hourly, d=daily) whereas the source dataset only contains snapshot h3, and the include/exclude policy selects h1,h2,h3,d1, then delete snapshots h1,h2,d1 on the destination dataset to make it 'the same'. On the other hand, if the include/exclude policy only selects snapshots h1,h2,h3 then only delete snapshots h1,h2 on the destination dataset to make it 'the same'.

  Note: To delete snapshots regardless, consider using --delete-dst-snapshots in combination with a source that is an empty dataset, such as the hardcoded virtual dataset named 'dummy', like so: bzfs dummy tank2/boo/bar --dryrun --skip-replication --delete-dst-snapshots --include-snapshot-regex '.*_daily' --recursive

  Note: Use --delete-dst-snapshots=bookmarks to delete bookmarks instead of snapshots, in which case no snapshots are selected and the --{include|exclude}-snapshot-* filter options treat bookmarks as snapshots wrt. selecting.

  Performance Note: --delete-dst-snapshots operates on multiple datasets in parallel (and serially within a dataset), using the same dataset order as bzfs replication. The degree of parallelism is configurable with the --threads option (see below).

--delete-dst-snapshots-no-crosscheck

• This flag indicates that --delete-dst-snapshots=snapshots shall check the source dataset only for a snapshot with the same GUID, and ignore whether a bookmark with the same GUID is present in the source dataset. Similarly, it also indicates that --delete-dst-snapshots=bookmarks shall check the source dataset only for a bookmark with the same GUID, and ignore whether a snapshot with the same GUID is present in the source dataset.

--delete-dst-snapshots-except

• This flag indicates that the --include/exclude-snapshot-* options shall have inverted semantics for the --delete-dst-snapshots option, thus deleting all snapshots except for the selected snapshots (within the specified datasets), instead of deleting all selected snapshots (within the specified datasets). In other words, this flag enables to specify which snapshots to retain instead of which snapshots to delete.

--delete-dst-snapshots-except-plan DICT_STRING

• Retention periods to be used if pruning snapshots or bookmarks within the selected destination datasets via --delete-dst-snapshots. Has the same format as --create-src-snapshots-plan. Snapshots (--delete-dst-snapshots=snapshots) or bookmarks (with --delete-dst-snapshots=bookmarks) that do not match a period will be deleted. To avoid unexpected surprises, make sure to carefully specify ALL snapshot names and periods that shall be retained, in combination with --dryrun.

  Example: "{'prod': {'onsite': {'secondly': 40, 'minutely': 40, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}, 'us-west-1': {'secondly': 0, 'minutely': 0, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}, 'eu-west-1': {'secondly': 0, 'minutely': 0, 'hourly': 36, 'daily': 31, 'weekly': 12, 'monthly': 18, 'yearly': 5}}, 'test': {'offsite': {'12hourly': 42, 'weekly': 12}, 'onsite': {'100millisecondly': 42}}}". This example will, for the organization 'prod' and the intended logical target 'onsite', retain secondly snapshots that were created less than 40 seconds ago, yet retain the latest 40 secondly snapshots regardless of creation time. Analog for the latest 40 minutely snapshots, latest 36 hourly snapshots, etc. It will also retain snapshots for the targets 'us-west-1' and 'eu-west-1' within the 'prod' organization. In addition, within the 'test' organization, it will retain snapshots that are created every 12 hours and every week as specified, and name them as being intended for the 'offsite' replication target. Analog for snapshots that are taken every 100 milliseconds within the 'test' organization. All other snapshots within the selected datasets will be deleted - you've been warned!

  The example scans the selected ZFS datasets for snapshots with names like prod_onsite_<timestamp>_secondly, prod_onsite_<timestamp>_minutely, prod_us-west-1_<timestamp>_hourly, prod_us-west-1_<timestamp>_daily, prod_eu-west-1_<timestamp>_hourly, prod_eu-west-1_<timestamp>_daily, test_offsite_<timestamp>_12hourly, test_offsite_<timestamp>_weekly, and so on, and deletes all snapshots that do not match a retention rule.

  Note: A zero within a period (e.g. 'hourly': 0) indicates that no snapshots shall be retained for the given period.

  Note: --delete-dst-snapshots-except-plan is a convenience option that auto-generates a series of the following other options: --delete-dst-snapshots-except, --new-snapshot-filter-group, --include-snapshot-regex, --include-snapshot-times-and-ranks

--delete-empty-dst-datasets [{snapshots,snapshots+bookmarks}]

• Do nothing if the --delete-empty-dst-datasets option is missing or --recursive is missing. Otherwise, after successful replication step and successful --delete-dst-datasets and successful --delete-dst-snapshots steps, if any, delete any selected destination dataset that has no snapshot and no bookmark if all descendants of that destination dataset are also selected and do not have a snapshot or bookmark either (again, only if the existing destination dataset is selected via --{include|exclude}-dataset* policy). Never delete non-selected dataset subtrees or their ancestors.

  For example, if the destination contains datasets h1,d1, and the include/exclude policy selects h1,d1, then check if h1,d1 can be deleted. On the other hand, if the include/exclude policy only selects h1 then only check if h1 can be deleted.

  Note: Use --delete-empty-dst-datasets=snapshots to delete snapshot-less datasets even if they still contain bookmarks.

--monitor-snapshots DICT_STRING

• Do nothing if the --monitor-snapshots flag is missing. Otherwise, after all other steps, alert the user if the ZFS 'creation' time property of the latest snapshot for any specified snapshot name pattern within the selected datasets is too old wrt. the specified age limit. The purpose is to check if snapshots are successfully taken on schedule, successfully replicated on schedule, and successfully pruned on schedule. Process exit code is 0, 1, 2 on OK, WARNING, CRITICAL, respectively. Example DICT_STRING: "{'prod': {'onsite': {'100millisecondly': {'latest': {'warning': '300 milliseconds', 'critical': '2 seconds'}}, 'secondly': {'latest': {'warning': '2 seconds', 'critical': '14 seconds'}}, 'minutely': {'latest': {'warning': '30 seconds', 'critical': '300 seconds'}}, 'hourly': {'latest': {'warning': '30 minutes', 'critical': '300 minutes'}}, 'daily': {'latest': {'warning': '4 hours', 'critical': '8 hours'}}, 'weekly': {'latest': {'warning': '2 days', 'critical': '8 days'}}, 'monthly': {'latest': {'warning': '2 days', 'critical': '8 days'}}, 'yearly': {'latest': {'warning': '5 days', 'critical': '14 days'}}, '10minutely': {'latest': {'warning': '0 minutes', 'critical': '0 minutes'}}}, '': {'daily': {'latest': {'warning': '4 hours', 'critical': '8 hours'}}}}}". This example alerts the user if the latest src or dst snapshot named prod_onsite_<timestamp>_hourly is more than 30 minutes late (i.e. more than 30+60=90 minutes old) [warning] or more than 300 minutes late (i.e. more than 300+60=360 minutes old) [critical]. Analog for the latest snapshot named prod_<timestamp>_daily, and so on.

  Note: A duration that is missing or zero (e.g. '0 minutes') indicates that no snapshots shall be checked for the given snapshot name pattern.

--monitor-snapshots-dont-warn

• Log a message for monitoring warnings but nonetheless exit with zero exit code.

--monitor-snapshots-dont-crit

• Log a message for monitoring criticals but nonetheless exit with zero exit code.

--compare-snapshot-lists [{src,dst,all,src+dst,src+all,dst+all,src+dst+all}]

• Do nothing if the --compare-snapshot-lists option is missing. Otherwise, after successful replication step and successful --delete-dst-datasets, --delete-dst-snapshots steps and --delete-empty-dst-datasets steps, if any, proceed as follows:

  Compare source and destination dataset trees recursively wrt. snapshots, for example to check if all recently taken snapshots have been successfully replicated by a periodic job.

  Example: List snapshots only contained in source (tagged with 'src'), only contained in destination (tagged with 'dst'), and contained in both source and destination (tagged with 'all'), restricted to hourly and daily snapshots taken within the last 7 days, excluding the last 4 hours (to allow for some slack/stragglers), excluding temporary datasets: bzfs tank1/foo/bar tank2/boo/bar --skip-replication --compare-snapshot-lists=src+dst+all --recursive --include-snapshot-regex '.*_(hourly|daily)' --include-snapshot-times-and-ranks '7 days ago..4 hours ago' --exclude-dataset-regex 'tmp.*'

  This outputs a TSV file containing the following columns:

  location creation_iso createtxg rel_name guid root_dataset rel_dataset name creation written

  Example output row:

  src 2024-11-06_08:30:05 17435050 /foo@test_2024-11-06_08:30:05_daily 2406491805272097867 tank1/src /foo tank1/src/foo@test_2024-10-06_08:30:04_daily 1730878205 24576

  If the TSV output file contains zero lines starting with the prefix 'src' and zero lines starting with the prefix 'dst' then no source snapshots are missing on the destination, and no destination snapshots are missing on the source, indicating that the periodic replication and pruning jobs perform as expected. The TSV output is sorted by rel_dataset, and by ZFS creation time within each rel_dataset - the first and last line prefixed with 'all' contains the metadata of the oldest and latest common snapshot, respectively. Third party tools can use this info for post-processing, for example using custom scripts using 'csplit' or duckdb analytics queries.

  The --compare-snapshot-lists option also directly logs various summary stats, such as the metadata of the latest common snapshot, latest snapshots and oldest snapshots, as well as the time diff between the latest common snapshot and latest snapshot only in src (and only in dst), as well as how many src snapshots and how many GB of data are missing on dst, etc.

  Note: Consider omitting the 'all' flag to reduce noise and instead focus on missing snapshots only, like so: --compare-snapshot-lists=src+dst

  Note: The source can also be an empty dataset, such as the hardcoded virtual dataset named 'dummy'.

  Note: --compare-snapshot-lists is typically much faster than standard 'zfs list -t snapshot' CLI usage because the former issues requests with a higher degree of parallelism than the latter. The degree is configurable with the --threads option (see below).

--dryrun [{recv,send}], -n [{recv,send}]

• Do a dry run (aka 'no-op') to print what operations would happen if the command were to be executed for real (optional). This option treats both the ZFS source and destination as read-only. Accepts an optional argument for fine tuning that is handled as follows:

  a) 'recv': Send snapshot data via 'zfs send' to the destination host and receive it there via 'zfs receive -n', which discards the received data there.

  b) 'send': Do not execute 'zfs send' and do not execute 'zfs receive'. This is a less 'realistic' form of dry run, but much faster, especially for large snapshots and slow networks/disks, as no snapshot is actually transferred between source and destination. This is the default when specifying --dryrun.

  Examples: --dryrun, --dryrun=send, --dryrun=recv

--verbose, -v

• Print verbose information. This option can be specified multiple times to increase the level of verbosity. To print what ZFS/SSH operation exactly is happening (or would happen), add the -v -v flag, maybe along with --dryrun. All ZFS and SSH commands (even with --dryrun) are logged such that they can be inspected, copy-and-pasted into a terminal shell and run manually to help anticipate or diagnose issues. ERROR, WARN, INFO, DEBUG, TRACE output lines are identified by [E], [W], [I], [D], [T] prefixes, respectively.

--quiet, -q

• Suppress non-error, info, debug, and trace output.

--no-privilege-elevation, -p

• Do not attempt to run state changing ZFS operations 'zfs create/rollback/destroy/send/receive/snapshot' as root (via 'sudo -u root' elevation granted by administrators appending the following to /etc/sudoers: <NON_ROOT_USER_NAME> ALL=NOPASSWD:/path/to/zfs

  Instead, the --no-privilege-elevation flag is for non-root users that have been granted corresponding ZFS permissions by administrators via 'zfs allow' delegation mechanism, like so: sudo zfs allow -u $SRC_NON_ROOT_USER_NAME snapshot,destroy,send,bookmark,hold $SRC_DATASET; sudo zfs allow -u $DST_NON_ROOT_USER_NAME mount,create,receive,rollback,destroy,canmount,mountpoint,readonly,compression,encryption,keylocation,recordsize $DST_DATASET_OR_POOL.

  For extra security $SRC_NON_ROOT_USER_NAME should be different than $DST_NON_ROOT_USER_NAME, i.e. the sending Unix user on the source and the receiving Unix user at the destination should be separate Unix user accounts with separate private keys even if both accounts reside on the same machine, per the principle of least privilege. Further, if you do not plan to use the --force* flags and --delete-* CLI options then ZFS permissions 'rollback,destroy' can be omitted. If you do not plan to customize the respective ZFS dataset property then ZFS permissions 'canmount,mountpoint,readonly,compression,encryption,keylocation,recordsize' can be omitted, arriving at the absolutely minimal set of required destination permissions: mount,create,receive.

  Also see https://openzfs.github.io/openzfs-docs/man/master/8/zfs-allow.8.html#EXAMPLES and https://tinyurl.com/9h97kh8n and https://youtu.be/o_jr13Z9f1k?si=7shzmIQJpzNJV6cq

--no-stream

• During replication, only replicate the most recent selected source snapshot of a dataset (using -i incrementals instead of -I incrementals), hence skip all intermediate source snapshots that may exist between that and the most recent common snapshot. If there is no common snapshot also skip all other source snapshots for the dataset, except for the most recent selected source snapshot. This option helps the destination to 'catch up' with the source ASAP, consuming a minimum of disk space, at the expense of reducing reliable options for rolling back to intermediate snapshots in the future.

--no-resume-recv

• Replication of snapshots via 'zfs send/receive' can be interrupted by intermittent network hiccups, reboots, hardware issues, etc. Interrupted 'zfs send/receive' operations are retried if the --retries and --retry-* options enable it (see above). In normal operation bzfs automatically retries such that only the portion of the snapshot is transmitted that has not yet been fully received on the destination. For example, this helps to progressively transfer a large individual snapshot over a wireless network in a timely manner despite frequent intermittent network hiccups. This optimization is called 'resume receive' and uses the 'zfs receive -s' and 'zfs send -t' feature.

  The --no-resume-recv option disables this optimization such that a retry now retransmits the entire snapshot from scratch, which could slow down or even prohibit progress in case of frequent network hiccups. bzfs automatically falls back to using the --no-resume-recv option if it is auto-detected that the ZFS pool does not reliably support the 'resume receive' optimization.

  Note: Snapshots that have already been fully transferred as part of the current 'zfs send/receive' operation need not be retransmitted regardless of the --no-resume-recv flag. For example, assume a single 'zfs send/receive' operation is transferring incremental snapshots 1 through 10 via 'zfs send -I', but the operation fails while transferring snapshot 10, then snapshots 1 through 9 need not be retransmitted regardless of the --no-resume-recv flag, as these snapshots have already been successfully received at the destination either way.

--no-create-bookmark

• For increased safety, in normal operation bzfs replication behaves as follows wrt. ZFS bookmark creation, if it is autodetected that the source ZFS pool support bookmarks: Whenever it has successfully completed replication of the most recent source snapshot, bzfs creates a ZFS bookmark of that snapshot and attaches it to the source dataset. Bookmarks exist so an incremental stream can continue to be sent from the source dataset without having to keep the already replicated snapshot around on the source dataset until the next upcoming snapshot has been successfully replicated. This way you can send the snapshot from the source dataset to another host, then bookmark the snapshot on the source dataset, then delete the snapshot from the source dataset to save disk space, and then still incrementally send the next upcoming snapshot from the source dataset to the other host by referring to the bookmark.

  The --no-create-bookmark option disables this safety feature but is discouraged, because bookmarks are tiny and relatively cheap and help to ensure that ZFS replication can continue even if source and destination dataset somehow have no common snapshot anymore. For example, if a pruning script has accidentally deleted too many (or even all) snapshots on the source dataset in an effort to reclaim disk space, replication can still proceed because it can use the info in the bookmark (the bookmark must still exist in the source dataset) instead of the info in the metadata of the (now missing) source snapshot.

  A ZFS bookmark is a tiny bit of metadata extracted from a ZFS snapshot by the 'zfs bookmark' CLI, and attached to a dataset, much like a ZFS snapshot. Note that a ZFS bookmark does not contain user data; instead a ZFS bookmark is essentially a tiny pointer in the form of the GUID of the snapshot and 64-bit transaction group number of the snapshot and creation time of the snapshot, which is sufficient to tell the destination ZFS pool how to find the destination snapshot corresponding to the source bookmark and (potentially already deleted) source snapshot. A bookmark can be fed into 'zfs send' as the source of an incremental send. Note that while a bookmark allows for its snapshot to be deleted on the source after successful replication, it still requires that its snapshot is not somehow deleted prematurely on the destination dataset, so be mindful of that. By convention, a bookmark created by bzfs has the same name as its corresponding snapshot, the only difference being the leading '#' separator instead of the leading '@' separator. Also see https://www.youtube.com/watch?v=LaNgoAZeTww&t=316s.

  You can list bookmarks, like so: zfs list -t bookmark -o name,guid,createtxg,creation -d 1 $SRC_DATASET, and you can (and should) periodically prune obsolete bookmarks just like snapshots, like so: zfs destroy $SRC_DATASET#$BOOKMARK. Typically, bookmarks should be pruned less aggressively than snapshots, and destination snapshots should be pruned less aggressively than source snapshots. As an example starting point, here is a command that deletes all bookmarks older than 90 days, but retains the latest 200 bookmarks (per dataset) regardless of creation time: bzfs dummy tank2/boo/bar --dryrun --recursive --skip-replication --delete-dst-snapshots=bookmarks --include-snapshot-times-and-ranks notime 'all except latest 200' --include-snapshot-times-and-ranks 'anytime..90 days ago'

--no-use-bookmark

• For increased safety, in normal replication operation bzfs replication also looks for bookmarks (in addition to snapshots) on the source dataset in order to find the most recent common snapshot wrt. the destination dataset, if it is auto-detected that the source ZFS pool support bookmarks. The --no-use-bookmark option disables this safety feature but is discouraged, because bookmarks help to ensure that ZFS replication can continue even if source and destination dataset somehow have no common snapshot anymore.

  Note that it does not matter whether a bookmark was created by bzfs or a third party script, as only the GUID of the bookmark and the GUID of the snapshot is considered for comparison, and ZFS guarantees that any bookmark of a given snapshot automatically has the same GUID, transaction group number and creation time as the snapshot. Also note that you can create, delete and prune bookmarks any way you like, as bzfs (without --no-use-bookmark) will happily work with whatever bookmarks currently exist, if any.

--ssh-cipher STRING

• SSH cipher specification for encrypting the session (optional); will be passed into ssh -c CLI. --ssh-cipher is a comma-separated list of ciphers listed in order of preference. See the 'Ciphers' keyword in ssh_config(5) for more information: https://manpages.ubuntu.com/manpages/man5/sshd_config.5.html. Default: ^[e-mail]

--ssh-src-private-key FILE

• Path to SSH private key file on local host to connect to src (optional); will be passed into ssh -i CLI. This option can be specified multiple times. default: $HOME/.ssh/id_rsa

--ssh-dst-private-key FILE

• Path to SSH private key file on local host to connect to dst (optional); will be passed into ssh -i CLI. This option can be specified multiple times. default: $HOME/.ssh/id_rsa

--ssh-src-user STRING

• Remote SSH username on src host to connect to (optional). Overrides username given in SRC_DATASET.

--ssh-dst-user STRING

• Remote SSH username on dst host to connect to (optional). Overrides username given in DST_DATASET.

--ssh-src-host STRING

• Remote SSH hostname of src host to connect to (optional). Can also be an IPv4 or IPv6 address. Overrides hostname given in SRC_DATASET.

--ssh-dst-host STRING

• Remote SSH hostname of dst host to connect to (optional). Can also be an IPv4 or IPv6 address. Overrides hostname given in DST_DATASET.

--ssh-src-port INT

• Remote SSH port on src host to connect to (optional).

--ssh-dst-port INT

• Remote SSH port on dst host to connect to (optional).

--ssh-src-extra-opts STRING

• Additional options to be passed to ssh CLI when connecting to src host (optional). The value is split on runs of one or more whitespace characters. Example: --ssh-src-extra-opts='-v -v' to debug ssh config issues.

--ssh-src-extra-opt STRING

• Additional option to be passed to ssh CLI when connecting to src host (optional). The value can contain spaces and is not split. This option can be specified multiple times. Example: --ssh-src-extra-opt='-oProxyCommand=nc %h %p' to disable the TCP_NODELAY socket option for OpenSSH.

--ssh-dst-extra-opts STRING

• Additional options to be passed to ssh CLI when connecting to dst host (optional). The value is split on runs of one or more whitespace characters. Example: --ssh-dst-extra-opts='-v -v' to debug ssh config issues.

--ssh-dst-extra-opt STRING

• Additional option to be passed to ssh CLI when connecting to dst host (optional). The value can contain spaces and is not split. This option can be specified multiple times. Example: --ssh-dst-extra-opt='-oProxyCommand=nc %h %p' to disable the TCP_NODELAY socket option for OpenSSH.

--ssh-src-config-file FILE

• Path to SSH ssh_config(5) file to connect to src (optional); will be passed into ssh -F CLI.

--ssh-dst-config-file FILE

• Path to SSH ssh_config(5) file to connect to dst (optional); will be passed into ssh -F CLI.

--threads INT[%]

• The maximum number of threads to use for parallel operations; can be given as a positive integer, optionally followed by the % percent character (min: 1, default: 100%). Percentages are relative to the number of CPU cores on the machine. Example: 200% uses twice as many threads as there are cores on the machine; 75% uses num_threads = num_cores * 0.75. Currently this option only applies to dataset and snapshot replication, --create-src-snapshots, --delete-dst-snapshots, --delete-empty-dst-datasets, --monitor-snapshots and --compare-snapshot-lists. The ideal value for this parameter depends on the use case and its performance requirements, as well as the number of available CPU cores and the parallelism offered by SSDs vs. HDDs, ZFS topology and configuration, as well as the network bandwidth and other workloads simultaneously running on the system. The current default is geared towards a high degreee of parallelism, and as such may perform poorly on HDDs. Examples: 1, 4, 75%, 150%

--max-concurrent-ssh-sessions-per-tcp-connection INT

• For best throughput, bzfs uses multiple SSH TCP connections in parallel, as indicated by --threads (see above). For best startup latency, each such parallel TCP connection can carry a maximum of S concurrent SSH sessions, where S=--max-concurrent-ssh-sessions-per-tcp-connection (default: 8, min: 1). Concurrent SSH sessions are mostly used for metadata operations such as listing ZFS datasets and their snapshots. This client-side max sessions parameter must not be higher than the server-side sshd_config(5) MaxSessions parameter (which defaults to 10, see https://manpages.ubuntu.com/manpages/latest/man5/sshd_config.5.html).

  Note: For better throughput, bzfs uses one dedicated TCP connection per ZFS send/receive operation such that the dedicated connection is never used by any other concurrent SSH session, effectively ignoring the value of the --max-concurrent-ssh-sessions-per-tcp-connection parameter in the ZFS send/receive case.

--bwlimit STRING

• Sets 'pv' bandwidth rate limit for zfs send/receive data transfer (optional). Example: 100m to cap throughput at 100 MB/sec. Default is unlimited. Also see https://manpages.ubuntu.com/manpages/latest/en/man1/pv.1.html

--compression-program STRING

• The name or path to the 'zstd' executable (optional). Default is 'zstd'. Examples: 'lz4', 'pigz', 'gzip', '/opt/bin/zstd'. Use '-' to disable the use of this program. The use is auto-disabled if data is transferred locally instead of via the network. This option is about transparent compression-on-the-wire, not about compression-at-rest.

--compression-program-opts STRING

• The options to be passed to the compression program on the compression step (optional). Default is '-1' (fastest).

--mbuffer-program STRING

• The name or path to the 'mbuffer' executable (optional). Default is 'mbuffer'. Use '-' to disable the use of this program. The use is auto-disabled if data is transferred locally instead of via the network. This tool is used to smooth out the rate of data flow and prevent bottlenecks caused by network latency or speed fluctuation.

--mbuffer-program-opts STRING

• Options to be passed to 'mbuffer' program (optional). Default: '-q -m 128M'.

--ps-program STRING

• The name or path to the 'ps' executable (optional). Default is 'ps'. Use '-' to disable the use of this program.

--pv-program STRING

• The name or path to the 'pv' executable (optional). Default is 'pv'. Use '-' to disable the use of this program. This is used for bandwidth rate-limiting and progress monitoring.

--pv-program-opts STRING

• The options to be passed to the 'pv' program (optional). Default: '--progress --timer --eta --fineta --rate --average-rate --bytes --interval=1 --width=120 --buffer-size=2M'.

--shell-program STRING

• The name or path to the 'sh' executable (optional). Default is 'sh'. Use '-' to disable the use of this program.

--ssh-program STRING

• The name or path to the 'ssh' executable (optional). Default is 'ssh'. Examples: 'hpnssh' or 'ssh' or '/opt/bin/ssh' or wrapper scripts around 'ssh'. Use '-' to disable the use of this program.

--sudo-program STRING

• The name or path to the 'sudo' executable (optional). Default is 'sudo'. Use '-' to disable the use of this program.

--zfs-program STRING

• The name or path to the 'zfs' executable (optional). Default is 'zfs'.

--zpool-program STRING

• The name or path to the 'zpool' executable (optional). Default is 'zpool'. Use '-' to disable the use of this program.

--log-dir DIR

• Path to the log output directory on local host (optional). Default: $HOME/bzfs-logs. The logger that is used by default writes log files there, in addition to the console. The current.dir symlink always points to the subdirectory containing the most recent log file. The current.log symlink always points to the most recent log file. The current.pv symlink always points to the most recent data transfer monitoring log. Run tail --follow=name --max-unchanged-stats=1 on both symlinks to follow what's currently going on. Parallel replication generates a separate .pv file per thread. To monitor these, run something like while true; do clear; for f in $(realpath $HOME/bzfs-logs/current/current.pv)*; do tac -s $(printf '\r') $f | tr '\r' '\n' | grep -m1 -v '^$'; done; sleep 1; done

--log-file-prefix STRING

• Default is zrun_. The path name of the log file on local host is ${--log-dir}/${--log-file-prefix}<timestamp>${--log-file-infix}${--log-file-suffix}-<random>.log. Example: --log-file-prefix=zrun_us-west-1_ --log-file-suffix=_daily will generate log file names such as zrun_us-west-1_2024-09-03_12:26:15_daily-bl4i1fth.log

--log-file-infix STRING

• Default is the empty string. The path name of the log file on local host is ${--log-dir}/${--log-file-prefix}<timestamp>${--log-file-infix}${--log-file-suffix}-<random>.log. Example: --log-file-prefix=zrun_us-west-1_ --log-file-suffix=_daily will generate log file names such as zrun_us-west-1_2024-09-03_12:26:15_daily-bl4i1fth.log

--log-file-suffix STRING

• Default is the empty string. The path name of the log file on local host is ${--log-dir}/${--log-file-prefix}<timestamp>${--log-file-infix}${--log-file-suffix}-<random>.log. Example: --log-file-prefix=zrun_us-west-1_ --log-file-suffix=_daily will generate log file names such as zrun_us-west-1_2024-09-03_12:26:15_daily-bl4i1fth.log

--log-subdir {daily,hourly,minutely}

• Make a new subdirectory in --log-dir every day, hour or minute; write log files there. Default is 'daily'.

--log-syslog-address STRING

• Host:port of the syslog machine to send messages to (e.g. 'foo.example.com:514' or '127.0.0.1:514'), or the file system path to the syslog socket file on localhost (e.g. '/dev/log'). The default is no address, i.e. do not log anything to syslog by default. See https://docs.python.org/3/library/logging.handlers.html#sysloghandler

--log-syslog-socktype {UDP,TCP}

• The socket type to use to connect if no local socket file system path is used. Default is 'UDP'.

--log-syslog-facility INT

• The local facility aka category that identifies msg sources in syslog (default: 1, min=0, max=7).

--log-syslog-prefix STRING

• The name to prepend to each message that is sent to syslog; identifies bzfs messages as opposed to messages from other sources. Default is 'bzfs'.

--log-syslog-level {CRITICAL,ERROR,WARN,INFO,DEBUG,TRACE}

• Only send messages with equal or higher priority than this log level to syslog. Default is 'ERROR'.

--log-config-file STRING

• The contents of a JSON file that defines a custom python logging configuration to be used (optional). If the option starts with a + prefix then the contents are read from the UTF-8 JSON file given after the + prefix. Examples: +log_config.json, +/path/to/log_config.json. Here is an example config file that demonstrates usage: https://github.com/whoschek/bzfs/blob/main/bzfs_tests/log_config.json

  For more examples see https://stackoverflow.com/questions/7507825/where-is-a-complete-example-of-logging-config-dictconfig and for details see https://docs.python.org/3/library/logging.config.html#configuration-dictionary-schema

  Note: Lines starting with a # character are ignored as comments within the JSON. Also, if a line ends with a # character the portion between that # character and the preceding # character on the same line is ignored as a comment.

--log-config-var NAME:VALUE [NAME:VALUE ...]

• User defined variables in the form of zero or more NAME:VALUE pairs (optional). These variables can be used within the JSON passed with --log-config-file (see above) via ${name[:default]} references, which are substituted (aka interpolated) as follows:

  If the variable contains a non-empty CLI value then that value is used. Else if a default value for the variable exists in the JSON file that default value is used. Else the program aborts with an error. Example: In the JSON variable ${syslog_address:/dev/log}, the variable name is 'syslog_address' and the default value is '/dev/log'. The default value is the portion after the optional : colon within the variable declaration. The default value is used if the CLI user does not specify a non-empty value via --log-config-var, for example via --log-config-var syslog_address:/path/to/socket_file or via --log-config-var syslog_address:[host,port].

  bzfs automatically supplies the following convenience variables: ${bzfs.log_level}, ${bzfs.log_dir}, ${bzfs.log_file}, ${bzfs.sub.logger}, ${bzfs.get_default_log_formatter}, ${bzfs.timestamp}. For a complete list see the source code of get_dict_config_logger().

--include-envvar-regex REGEX [REGEX ...]

• On program startup, unset all Unix environment variables for which the full environment variable name matches at least one of the excludes but none of the includes. If an environment variable is included this decision is never reconsidered because include takes precedence over exclude. The purpose is to tighten security and help guard against accidental inheritance or malicious injection of environment variable values that may have unintended effects.

  This option can be specified multiple times. A leading ! character indicates logical negation, i.e. the regex matches if the regex with the leading ! character removed does not match. The default is to include no environment variables, i.e. to make no exceptions to --exclude-envvar-regex. Example that retains at least these two env vars: --include-envvar-regex PATH --include-envvar-regex bzfs_min_pipe_transfer_size. Example that retains all environment variables without tightened security: '.*'

--exclude-envvar-regex REGEX [REGEX ...]

• Same syntax as --include-envvar-regex (see above) except that the default is to exclude no environment variables. Example: bzfs_.*

--version

• Display version information and exit.

--help, -h

• Show this help message and exit.

YEARLY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N years are scheduled to be created on the source by the --create-src-snapshots option.

--yearly_month INT

• The month within a year (1 ≤ x ≤ 12, default: 1).

--yearly_monthday INT

• The day within a month (1 ≤ x ≤ 31, default: 1).

--yearly_hour INT

• The hour within a day (0 ≤ x ≤ 23, default: 0).

--yearly_minute INT

• The minute within an hour (0 ≤ x ≤ 59, default: 0).

--yearly_second INT

• The second within a minute (0 ≤ x ≤ 59, default: 0).

MONTHLY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N months are scheduled to be created on the source by the --create-src-snapshots option.

--monthly_monthday INT

• The day within a month (1 ≤ x ≤ 31, default: 1).

--monthly_hour INT

• The hour within a day (0 ≤ x ≤ 23, default: 0).

--monthly_minute INT

• The minute within an hour (0 ≤ x ≤ 59, default: 0).

--monthly_second INT

• The second within a minute (0 ≤ x ≤ 59, default: 0).

WEEKLY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N weeks are scheduled to be created on the source by the --create-src-snapshots option.

--weekly_weekday INT

• The weekday within a week: 0=Sunday, 1=Monday, ..., 6=Saturday (0 ≤ x ≤ 6, default: 0).

--weekly_hour INT

• The hour within a day (0 ≤ x ≤ 23, default: 0).

--weekly_minute INT

• The minute within an hour (0 ≤ x ≤ 59, default: 0).

--weekly_second INT

• The second within a minute (0 ≤ x ≤ 59, default: 0).

DAILY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N days are scheduled to be created on the source by the --create-src-snapshots option.

--daily_hour INT

• The hour within a day (0 ≤ x ≤ 23, default: 0).

--daily_minute INT

• The minute within an hour (0 ≤ x ≤ 59, default: 0).

--daily_second INT

• The second within a minute (0 ≤ x ≤ 59, default: 0).

HOURLY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N hours are scheduled to be created on the source by the --create-src-snapshots option.

--hourly_minute INT

• The minute within an hour (0 ≤ x ≤ 59, default: 0).

--hourly_second INT

• The second within a minute (0 ≤ x ≤ 59, default: 0).

MINUTELY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N minutes are scheduled to be created on the source by the --create-src-snapshots option.

--minutely_second INT

• The second within a minute (0 ≤ x ≤ 59, default: 0).

SECONDLY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N seconds are scheduled to be created on the source by the --create-src-snapshots option.

--secondly_millisecond INT

• The millisecond within a second (0 ≤ x ≤ 999, default: 0).

MILLISECONDLY PERIOD ANCHORS

Use these options to customize when snapshots that happen every N milliseconds are scheduled to be created on the source by the --create-src-snapshots option.

--millisecondly_microsecond INT

• The microsecond within a millisecond (0 ≤ x ≤ 999, default: 0).

ZFS-RECV-O (EXPERIMENTAL)

The following group of parameters specifies additional zfs receive '-o' options that can be used to configure the copying of ZFS dataset properties from the source dataset to its corresponding destination dataset. The 'zfs-recv-o' group of parameters is applied before the 'zfs-recv-x' group.

--zfs-recv-o-targets {full,incremental,full+incremental}

• The zfs send phase or phases during which the extra '-o' options are passed to 'zfs receive'. This can be one of the following choices: 'full', 'incremental', 'full+incremental'. Default is 'full+incremental'. A 'full' send is sometimes also known as an 'initial' send.

--zfs-recv-o-sources STRING

• The ZFS sources to provide to the 'zfs get -s' CLI in order to fetch the ZFS dataset properties that will be fed into the --zfs-recv-o-include/exclude-regex filter (see below). The sources are in the form of a comma-separated list (no spaces) containing one or more of the following choices: 'local', 'default', 'inherited', 'temporary', 'received', 'none', with the default being 'local'. Uses 'zfs get -p -s $zfs-recv-o-sources all $SRC_DATASET' to fetch the properties to copy - https://openzfs.github.io/openzfs-docs/man/master/8/zfs-get.8.html. P.S: Note that the existing 'zfs send --props' option does not filter and that --props only reads properties from the 'local' ZFS property source (https://github.com/openzfs/zfs/issues/13024).

--zfs-recv-o-include-regex REGEX [REGEX ...]

• Take the output properties of --zfs-recv-o-sources (see above) and filter them such that we only retain the properties whose name matches at least one of the --include regexes but none of the --exclude regexes. If a property is excluded this decision is never reconsidered because exclude takes precedence over include. Append each retained property to the list of '-o' options in --zfs-recv-program-opt(s), unless another '-o' or '-x' option with the same name already exists therein. In other words, --zfs-recv-program-opt(s) takes precedence.

  The --zfs-recv-o-include-regex option can be specified multiple times. A leading ! character indicates logical negation, i.e. the regex matches if the regex with the leading ! character removed does not match. If the option starts with a + prefix then regexes are read from the newline-separated UTF-8 text file given after the + prefix, one regex per line inside of the text file.

  The default is to include no properties, thus by default no extra '-o' option is appended. Example: --zfs-recv-o-include-regex recordsize volblocksize. More examples: .* (include all properties), foo bar myapp:.* (include three regexes) +zfs-recv-o_regexes.txt, +/path/to/zfs-recv-o_regexes.txt

--zfs-recv-o-exclude-regex REGEX [REGEX ...]

• Same syntax as --zfs-recv-o-include-regex (see above), and the default is to exclude no properties. Example: --zfs-recv-o-exclude-regex encryptionroot keystatus origin volblocksize volsize

ZFS-RECV-X (EXPERIMENTAL)

The following group of parameters specifies additional zfs receive '-x' options that can be used to configure the copying of ZFS dataset properties from the source dataset to its corresponding destination dataset. The 'zfs-recv-o' group of parameters is applied before the 'zfs-recv-x' group.

--zfs-recv-x-targets {full,incremental,full+incremental}

• The zfs send phase or phases during which the extra '-x' options are passed to 'zfs receive'. This can be one of the following choices: 'full', 'incremental', 'full+incremental'. Default is 'full+incremental'. A 'full' send is sometimes also known as an 'initial' send.

--zfs-recv-x-sources STRING

• The ZFS sources to provide to the 'zfs get -s' CLI in order to fetch the ZFS dataset properties that will be fed into the --zfs-recv-x-include/exclude-regex filter (see below). The sources are in the form of a comma-separated list (no spaces) containing one or more of the following choices: 'local', 'default', 'inherited', 'temporary', 'received', 'none', with the default being 'local'. Uses 'zfs get -p -s $zfs-recv-x-sources all $SRC_DATASET' to fetch the properties to copy - https://openzfs.github.io/openzfs-docs/man/master/8/zfs-get.8.html. P.S: Note that the existing 'zfs send --props' option does not filter and that --props only reads properties from the 'local' ZFS property source (https://github.com/openzfs/zfs/issues/13024). Thus, -x opts do not benefit from source != 'local' (which is the default already).

--zfs-recv-x-include-regex REGEX [REGEX ...]

• Take the output properties of --zfs-recv-x-sources (see above) and filter them such that we only retain the properties whose name matches at least one of the --include regexes but none of the --exclude regexes. If a property is excluded this decision is never reconsidered because exclude takes precedence over include. Append each retained property to the list of '-x' options in --zfs-recv-program-opt(s), unless another '-o' or '-x' option with the same name already exists therein. In other words, --zfs-recv-program-opt(s) takes precedence.

  The --zfs-recv-x-include-regex option can be specified multiple times. A leading ! character indicates logical negation, i.e. the regex matches if the regex with the leading ! character removed does not match. If the option starts with a + prefix then regexes are read from the newline-separated UTF-8 text file given after the + prefix, one regex per line inside of the text file.

  The default is to include no properties, thus by default no extra '-x' option is appended. Example: --zfs-recv-x-include-regex recordsize volblocksize. More examples: .* (include all properties), foo bar myapp:.* (include three regexes) +zfs-recv-x_regexes.txt, +/path/to/zfs-recv-x_regexes.txt

--zfs-recv-x-exclude-regex REGEX [REGEX ...]

• Same syntax as --zfs-recv-x-include-regex (see above), and the default is to exclude no properties. Example: --zfs-recv-x-exclude-regex encryptionroot keystatus origin volblocksize volsize