ZFS Sanoid Post-Hook Success ZFS Diff Script

mokfarg · May 6, 2025

Hello! If anyone like me likes to verify what files have changed between zfs snapshots, I have a simple post-hook success zfs diff script I use with Sanoid. You are free to use it, I kept it simple. Take it as is or give suggestions if you think you can make it better. Take care!

sh:

#!/bin/sh
# Sanoid post-hook to log ZFS snapshot diffs via syslog (FreeBSD style)

CONFIG_FILE="/usr/local/etc/zfs-diff.conf"
: "${SYSLOG_TAG:=zfs-diff}"
: "${SYSLOG_FACILITY:=local0}"
: "${SNAPSHOT_TYPE:=hourly}"

[ $# -eq 1 ] && CONFIG_FILE="$1"
[ -f "$CONFIG_FILE" ] && . "$CONFIG_FILE"

log() {
    logger -p "${SYSLOG_FACILITY}.$1" -t "$SYSLOG_TAG" -- "$2"
}

[ -z "$TARGET_DATASETS" ] && log warn "No TARGET_DATASETS set" && exit 0

for ds in $TARGET_DATASETS; do
    zfs list "$ds" >/dev/null 2>&1 || {
        log warn "Dataset '$ds' not found"
        continue
    }

    snaps=$(zfs list -t snapshot -o name -s creation -r "$ds" 2>/dev/null |
        grep "^$ds@autosnap_.*_${SNAPSHOT_TYPE}$" | tail -n 2)

    set -- $snaps
    [ $# -lt 2 ] && log warn "$ds: fewer than 2 '${SNAPSHOT_TYPE}' snapshots" && continue

    log info "zfs diff '$1' '$2'"
    zfs diff -FHh "$1" "$2" 2>&1 | while IFS= read -r line; do
        [ -n "$line" ] && log info "$line"
    done

Example of conf file:

Code:

TARGET_DATASETS="tank/dataset1"
SYSLOG_TAG="zfs-diff"
SYSLOG_FACILITY="local0"
SNAPSHOT_TYPE="hourly"

ZFS Sanoid Post-Hook Success ZFS Diff Script

mokfarg