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POSIX compliant shell script to manage ZFS snapshot replication locally, or between hosts.

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# zfs-replicate

A POSIX shell script to automate ZFS Replication.

## Features

- The script follows strict POSIX standards and should be usable on any host with a POSIX compliant shell.
- Source pools and datasets are always authoritative, the script will always defer to the source.
- Supports push and pull replication with local and remote datasets.
- Supports multiple pool/dataset pairs to replicate.
- Supports divergence detection and reconciliation of destination datasets.
- Logging leverages syslog (via logger) by default, but local logging may be configured.
- Includes a well documented `config.sh` file that may be used as configuration or as reference for environment
  variables passed to the script.
- May be run on any schedule using cron or similar mechanism.
- Fully source compliant and may be used by other scripts.
- Test coverage of core functions via mocks in the test/test.sh script.
- Includes a `--status` option for XigmaNAS that can be used to email the last log output at your preferred schedule.
  Simply add it as a custom script in the email settings under "System > Advanced > Email Reports"

## FreeBSD Package

This script is available in the FreeBSD [package and ports tree](https://www.freshports.org/sysutils/zfs-replicate/).

Special thanks to [@tschettervictor](https://www.github.com/tschettervictor) for taking over maintenance of the
package, suggesting new features, and testing for the v1.0 release.
This script has been published to GitHub since 2012 and largely untouched since 2017. The v1.0 release updates mark
the first major changes to this script in over 7 years.

## Warning

Replicating to a root dataset will rewrite the remote pool with forced replication.
This script will create a true 1:1 copy of the source dataset in the destination dataset with default options.

The configuration `REPLICATE_SETS="zpoolOne:zpoolTwo"` will result in `zpoolTwo` being a 1:1 copy of `zpoolOne` and may
result in data loss on `zpoolTwo`.

To replicate a root dataset safely to another pool consider `REPLICATE_SETS="zpoolOne:zpoolTwo/zpoolOne"` instead.

This will result in a 1:1 copy of `zpoolOne` in a separate dataset of `zpoolTwo` and will not affect other datasets
currently present on the destination.

## Configuration

Configuration is done via an optional config file as environment variables. Most options have sane
defaults to keep configuration to a minimum. The script will attempt to locate a file called `config.sh` in the same
directory as the script if one is not passed via the command line.

The config file is very well commented and the contents of the sample config are shown below. The only required
setting without a default is the `REPLICATE_SETS` option. The script will error out on launch if required configuration
is not met.

### Available Command Line Options

```text
Usage: ./zfs-replicate.sh [config] [options]

POSIX shell script to automate ZFS Replication

Options:
  -c, --config <configFile>    configuration file
  -s, --status                 print most recent log messages to stdout
  -h, --help                   show this message
```

### Config File and Environment Variable Reference

```sh
#!/usr/bin/env sh
## zfs-replicate configuration file
# shellcheck disable=SC2034

## Datasets to replicate. These must be zfs paths not mount points.
## The format general format is "source:destination". The source is always
## considered authoritative. This holds true for reconciliation attempts with
## the "ALLOW_RECONCILIATION" option described below as well.
##
## Examples replicating a local source to a remote destination (PUSH):
##   - sourcePool/sourceDataset:destinationPool@host
##   - sourcePool/sourceDataset:destinationPool/destinationDataset@host
## Examples replicating from a remote source to a local destination (PULL):
##   - sourcePool/sourceDataset@host:destinationPool
##   - sourcePool/sourceDataset@host:destinationPool/destinationDataset
## Examples replicating a local source to a local destination:
##   - sourcePool/sourceDataset:destinationPool
##   - sourcePool/sourceDataset:destinationPool/destinationDataset
## Multiple space separated sets may be specified.
## Pools and dataset pairs must exist on the respective servers.
##
#REPLICATE_SETS=""

## Allow replication of root datasets.
## If "REPLICATE_SETS" contains root datasets and "ALLOW_ROOT_DATASETS" is
## NOT set to 1, root datasets will be skipped and a warning will be printed.
##
## 0 - disable (default)
## 1 - enable (use at your own risk)
##
#ALLOW_ROOT_DATASETS=0

## Manual alteration of the source or destination datasets by removing
## snapshots often results in failure. It is expected that datasets configured
## for replication are a 1:1 copy of each other after the first script run.
## Setting this option to "1" allows the script to attempt reconciliation when
## source and destination datasets have diverged.
##
## NOTE: The source is always authoritative. Reconciliation will only
## affect the destination dataset. This script will NEVER modify the source
## as a means to prevent reconcile divergence between datasets.
##
## Setting this option to "1" will result in the following potentially
## destructive behavior for the destination dataset.
##
## - If the script is unable to find the source base snapshot
##   in the destination dataset. The script will fallback to a full send.
##   When combined with the "-F" option in the destination receive pipe,
##   this option will force a reconciliation. ZFS will automatically remove
##   snapshots in the destination that do not exist within the source.
## - If the script determines that replication snapshots exist in the
##   destination dataset, and no base snapshot is present in the source.
##   The script will remove ALL destination snapshots that appear to have been
##   created by this script and instruct ZFS to do a full send of the source
##   to the destination.
##
## These scenarios should never happen under normal circumstances.
## Setting "ALLOW_RECONCILIATION" to "1" will allow the script to push
## past failures caused by divergent source and destination datasets to
## create a 1:1 copy of the source in the destination.
##
## 0 - disable (default)
## 1 - enable (use at your own risk)
##
#ALLOW_RECONCILIATION=0

## Option to recursively snapshot children of datasets contained
## in the replication set.
##
## 0 - disable (default)
## 1 - enable
##
#RECURSE_CHILDREN=0

## The number of snapshots to keep for each dataset.
## Older snapshots, by creation date, will be deleted.
## A minimum of 2 snapshots must be kept for replication to work.
## This defaults to 2 if not set.
##
#SNAP_KEEP=2

## Option to write logs to syslog via the "logger" tool. This option
## may be enabled or disabled independently from log file settings.
##
## 0 - disable
## 1 - enable (default)
##
#SYSLOG=1

## Optional logging facility to use with syslog. The default facility
## is "user" unless changed below. Other common options include local
## facilities 0-7.
## Example: local0, local1, local2, local3, local4, local5, local6, or local7
##
#SYSLOG_FACILITY="user"

## The following substitutions for current date information
## may be used in the "TAG" setting below.
## These are evaluated at runtime.
##   - %DOW% = Day of Week (date "+%a")
##   - %MOY% = Month of Year (date "+%m")
##   - %DOM% = Day of Month (date "+%d")
##   - %CYR% = Current Year (date "+%Y")
##   - %NOW% = Current Unixtime (date "+%s")

## String used for snapshot names and log tags.
## Example: pool0/someplace@autorep-08242024_1724527527
## The default is "%MOY%%DOM%%CYR%_%NOW%"
##
#TAG="%MOY%%DOM%%CYR%_%NOW%"

## The log file needs to start with "autorep-" in order for log cleanup
## to work using the default below is strongly suggested. Leaving this commented out
## will disable the writing of the standalone log file. The "%TAG%" substitution
## and/or other date substitutions may be used. The default is "autorep-%TAG%.log"
## When enabled logs will be placed under the "LOG_BASE" path set above.
##
#LOG_FILE="autorep-%TAG%.log"

## Number of log files to keep. Note, this is only used
## if "LOG_BASE" is set to a non-empty value above.
## Older logs, by creation date, will be deleted.
## This defaults to 5 if not set.
##
#LOG_KEEP=5

## Set the destination for physical log files to reside. By default
## logging is done via syslog. This setting will always be treated as a
## directory and not a file.
##
#LOG_BASE="/var/log/zfs-replicate"

## Path to the system "logger" executable.
## The default uses the first "logger" executable found in $PATH.
##
#LOGGER=$(which logger)

## Path to GNU "find" binary. Solaris find does not support the "-maxdepth"
## option, which is required to rotate log files.
## On solaris 11, GNU find is typically located at "/usr/bin/gfind".
## The default uses the first "find" executable in $PATH.
## This is NOT required when using syslog.
##
#FIND=$(which find)

## Path to the system "ssh" binary. You may also include custom arguments
## to SSH here or in the "DEST_PIPE_WITH_HOST" option above.
## Example: SSH="ssh -l root" to login as root to target host.
## The default uses the first "ssh" executable found in $PATH.
##
#SSH=$(which ssh)

## Path to the system "zfs" binary. The default uses the first "zfs"
## executable found in $PATH.
##
#ZFS=$(which zfs)

## Set the pipe to the destination pool. But DO NOT INCLUDE the pipe (|)
## character in this setting. Filesystem  names from the source will be
## sent to the destination. For increased transfer speed to remote hosts you
## may want to customize ssh ciphers or include mbuffer.
## The macro %HOST% string will be substituted with the value of the "@host"
## target in the replication set.
## The default WITH a "@host" option is "ssh %HOST% zfs receive -vFd"
## The default WITHOUT a "@host" option is "zfs receive -vFd".
##
#DEST_PIPE_WITH_HOST="$SSH %HOST% $ZFS receive -vFd"
#DEST_PIPE_WITHOUT_HOST="$ZFS receive -vFd"

## Command to check the health of a source or destination host.
## A return code of 0 is considered OK/available.
## This is only used when a replicate set contains an "@host" option.
## The macro string "%HOST%" will be substituted with the value of
## the "@host" target in the replicate set.
## The default command is "ping -c1 -q -W2 %HOST%".
##
#HOST_CHECK="ping -c1 -q -W2 %HOST%"
```

### With Environment Variables

```shell
LOG_BASE="./logs" SYSLOG=0 SSH="ssh -l root" REPLICATE_SETS="srcPool/srcFS:destPool/destFS@host" ./zfs-replicate.sh
```

## Notes

If you use this script, let me know. Report issues via GitHub so they may be resolved.

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