Generates fstab entries for a FreeBSD/TrueNAS jail of all available ZFS datasets (excluding 'boot-pool', '.system', and live 'iocage') so that a backup program in a jail (e.g. duplicati) can access the data and back it all up.

make_backup_fstab.py

#!/usr/local/bin/python

"""
make_backup_fstab.py
2021-03-15 by Graham R. Armstrong

Generates fstab entries for a FreeBSD/TrueNAS jail of all available ZFS
datasets (excluding 'boot-pool', '.system', and live 'iocage') so that
a backup program in a jail (e.g. duplicati) can access the data and back
it all up.
"""

import subprocess


OUTPUT_FILE = "fstab-append.txt"
PATH_TO_JAIL_ROOT = "/mnt/pool0/iocage/jails/duplicati-backup/root"


def include_dataset(dataset):
    parts = dataset.split('/')
    if len(parts) == 1:
        return False
    if parts[0] == "boot-pool":
        return False
    if parts[1] in ["iocage", ".system"]:
        return False
    return True


def main():
    # Step 1: Get a list of datasets and mountpoints
    pargs = ("zfs", "list", "-t", "filesystem", "-o", "name,mountpoint", "-rH")
    process = subprocess.Popen(pargs,
                               stdout=subprocess.PIPE,
                               stderr=subprocess.PIPE)
    stdout, stderr = process.communicate()

    # Jump ship if stderr has errors
    if stderr:
        raise Exception(stderr.decode("utf-8"))

    # Step 2: Parse output into a list of tuples
    lines = stdout.decode("utf-8").strip().split('\n')
    dataset_mounts = [line.split("\t") for line in lines]

    # Step 3: Filter out datasets we don't need, store mounts for ones we do
    mounts = []
    for dataset, mount in dataset_mounts:
        if mount in ["legacy", "/", "none"]:
            continue
        if include_dataset(dataset):
            mounts.append(mount)

    # Step 4: Prepend the jail prefix to create the mounts
    fstab_lines = []
    for mount in mounts:
        mount_point = PATH_TO_JAIL_ROOT + mount
        line = (mount, mount_point, "nullfs", "ro", "0", "0")
        fstab_lines.append('\t'.join(line))

    # Step 5: Write it to file
    with open(OUTPUT_FILE, "w") as handle:
        for line in fstab_lines:
            handle.write(line + "\n")


if __name__ == '__main__':
    main()