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ZFS snapshot tool written in Python

Project description


pyznap is a ZFS snapshot management tool. It automatically takes and deletes snapshots and can send them to different backup locations. You can specify a policy for a given filesystem in the pyznap.conf file and then use cron to let it run regularly. pyznap includes zfs bindings for python, forked and modified from

How does it work?

pyznap regularly takes and deletes snapshots according to a specified policy. You can take frequent, hourly, daily, weekly, monthly and yearly snapshots. 'frequent' snapshots can be taken up to once per minute, the frequency can be adjusted by the cronjob frequency. Old snapshots are deleted as you take new ones, thinning out the history as it gets older.

Datasets can also be replicated to other pools on the same system or remotely over ssh. After an initial sync, backups will be done incrementally as long as there are common snapshots between the source and the destination.


pyznap is written in python 3.5+ and requires the following packages:


For developing and running the tests you additionally need:


You also need the faketime program for some tests to simulate pyznap running over time.

I suggest installing virtualenv & virtualenvwrapper, so you don't clutter your system python installation with additional packages.

pyznap uses mbuffer to speed up zfs send/recv and pv to show progress, but also works if they are not installed.

Note that ZFS needs root access to run commands. Due to this you should install pyznap under your root user.

How do I set it up?

pyznap can easily be installed with pip. In your virtualenv just run

pip install pyznap

and pyznap & its requirements will be installed. This should also create an executable in your PATH, either at /path/to/virtualenv/pyznap/bin/pyznap or /usr/local/bin/pyznap. If you use your system python installation you might want to use the --user flag. In this case the executable will be located at ~/.local/bin/pyznap.

Before you can use pyznap, you will need to create a config file. For initial setup run

pyznap setup [-p PATH]

This will create a directory PATH (default is /etc/pyznap/) and copy a sample config there. A config for your system might look like this (remove the comments):

frequent = 4                          # Keep 4 frequent snapshots
hourly = 24                           # Keep 24 hourly snapshots
daily = 7                             # Keep 7 daily snapshots
weekly = 4                            # Keep 4 weekly snapshots
monthly = 6                           # Keep 6 monthly snapshots
yearly = 1                            # Keep 1 yearly snapshot
snap = yes                            # Take snapshots on this filesystem
clean = yes                           # Delete old snapshots on this filesystem
dest = backup/filesystem              # Backup this filesystem on this location

Then set up a cronjob by creating a file under /etc/cron.d/

nano /etc/cron.d/pyznap

and let pyznap run regularly by adding the following lines


*/15 * * * *   root    /path/to/pyznap snap >> /var/log/pyznap.log 2>&1

This will run pyznap every quarter hour to take and delete snapshots. 'frequent' snapshots can be taken up to once per minute, so adjust your cronjob accordingly.

If you also want to send your filesystems to another location you can add a line

0 0 * * *   root    /path/to/pyznap send >> /var/log/pyznap.log 2>&1

This will backup your data once per day at 12pm.

You can also manage and send to remote ssh locations. Always specify ssh locations with


A sample config which backs up a filesystem to a remote location looks like

hourly = 24
snap = yes
clean = yes
dest = ssh:22:user@host:backup/data   # Specify ssh destination
dest_keys = /home/user/.ssh/id_rsa    # Provide key for ssh login. If none given, look in home dir

I would also suggest making sure that root has ownership for all files, s.t. no user can modify them. If that is not the case just run

chown root:root -R /etc/pyznap/

Command line options

  • --config

    Specify config file. Default is /etc/pyznap/pyznap.conf.

  • setup [-p PATH]

    Initial setup. Creates a config dir and puts a sample config file there. You can specify the path to the config dir with the -p flag, default is /etc/pyznap/.

  • snap

    Interface to the snapshot management tool. Has three optional arguments:

    • --take

      Takes snapshots according to policy in the config file.

    • --clean

      Deletes old snapshots according to policy.

    • --full

      First takes snapshots, then deletes old ones. Default when no other option is given.

  • send

    Interface to the zfs send/receive tool. Has two usages:

    • No further option is given

      Send snapshots to backup locations according to policy.


      Send source filesystem to destination filesystem. If destination is a ssh location you can specify a keyfile with the -i flag.

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