Generates ZFS filesystem snapshots and leaves three trailing snaps

zfs-snapshot.sh

#!/usr/local/bin/bash

# num snapshots to hold back
KEEP=3

# Define the ZFS filesystem to snapshot
ZFS_FILESYSTEM="storage" 

# Define the snapshot name prefix
SNAPSHOT_PREFIX="snap"

# Get the current date in a suitable format for the snapshot name
SNAPSHOT_DATE=$(date +%Y%m%d%H%M%S)

# Create the new snapshot
echo "Creating new snapshot: $ZFS_FILESYSTEM@$SNAPSHOT_PREFIX-$SNAPSHOT_DATE"
zfs snapshot "$ZFS_FILESYSTEM@$SNAPSHOT_PREFIX-$SNAPSHOT_DATE"

# Get a list of snapshots for the specified filesystem, sorted by creation date (newest first)
# awk prints the snapshot name (first feild).
SNAPSHOTS=$(zfs list -t snapshot | grep "$ZFS_FILESYSTEM" | awk '{print $1}' | sort -r)
# Count the number of snapshots
NUM_SNAPSHOTS=$(echo "$SNAPSHOTS" | wc -l)
KEEPTAIL=$(($KEEP + 1))
# If there are more than two snapshots (newest + one old version)
if [ "$NUM_SNAPSHOTS" -gt $KEEP ]; then
  # Loop through snapshots to identify and destroy older ones, keeping only the two most recent
  # The snapshots are sorted newest first, so we want to keep the first two and destroy the rest.
  # 'tail -n +3' starts from the third line, effectively giving us snapshots older than the third newest.
  OLD_SNAPSHOTS=$(echo "$SNAPSHOTS" | tail -n +$KEEPTAIL)

  for OLD_SNAP in $OLD_SNAPSHOTS; do
    echo "Destroying old snapshot: $OLD_SNAP"
    zfs destroy "$OLD_SNAP"
  done
else
  echo "Fewer than two snapshots found, no old snapshots to delete."
fi
mailx -s "Fileserver: snapshot taken" [email protected] <<< \
"The fileserver has generated a filesystem snapshot of $ZFS_FILESYSTEM at $ZFS_FILESYSTEM@$SNAPSHOT_PREFIX-$SNAPSHOT_DATE"
echo "Snapshot process complete."