BTRFS: Automatic Snapshots Script

btrfsSnapshot.sh

#!/bin/bash

set -e          # Exit immediately if a command fails
set -u          # Treat unset variables as an error
set -o pipefail # Catch pipeline errors

## ebal, Mon, 07 Nov 2022 08:49:37 +0200
## ebal, Fri, 28 Nov 2025 23:41:22 +0200

## @daily /usr/local/bin/btrfs_subvolume_snapshot.sh

# Configuration

# paths MUST end with '/'
btrfs_paths=("/home/" "/opt/")

# Snapshot directory should be on the same disk for each btrfs path
btrfs_snap_dir=".Snapshot"

# approximately 3m (once per day)
keep_snapshots=21

# Generate timestamp - eg., 20240615_121530
timestamp=$(date +%Y%m%d_%H%M%S)
# hash for unique log directory per day - e.g., 2024/06/15
yymmdd=$(date +%Y/%m/%d)

# Log file setup
logdir="/var/log/btrfsSnapshot/${yymmdd}"
logfile="${logdir}/btrfsSnapshot_${timestamp}.log"

# Create log directory
mkdir -p "${logdir}"
mkdir -p "${btrfs_snap_dir}"

# Log start
echo -e "[$(date -R)] Starting Btrfs Snapshot Process" | tee -a "${logfile}"

for btrfs_path in "${btrfs_paths[@]}"; do
	# Echo line delimeter
	echo -e "\n= = = = = "

	BASENAME=$(basename "${btrfs_path}")

	# List btrfs subvolumes command
	btrfs_list="btrfs subvolume list -a -s -r --sort=+gen -t"

	## How many Snapshots are there?
	list_btrfs_snap=$(${btrfs_list} "${btrfs_path}" | { grep -i "${BASENAME}" || true; } | wc -l)
	echo -e "\nFound ${list_btrfs_snap} btrfs subvolume snapshots for ${btrfs_path}" | tee -a "${logfile}"

	## Get oldest rootfs btrfs snapshot and delete if necessary
	while [ "$list_btrfs_snap" -gt "$keep_snapshots" ]; do

		# Don't store the command as a string, execute it directly
		prev_btrfs_snap=$(${btrfs_list} "${btrfs_path}" | grep -i -m1 "${BASENAME}" | cut -f1 || true)
		echo -e "Found previous btrfs ${BASENAME} snapshot ID: ${prev_btrfs_snap}" | tee -a "${logfile}"

		# Check if we found a snapshot
		if [ -z "${prev_btrfs_snap}" ]; then
			echo "Error: Could not find snapshot to delete for ${BASENAME}" | tee -a "${logfile}"
			break
		fi

		## Delete a btrfs snapshot by their subvolume id
		btrfs subvolume delete --subvolid "${prev_btrfs_snap}" "${btrfs_path}" | tee -a "${logfile}"

		# Update list of snapshots after deletion
		list_btrfs_snap=$(${btrfs_list} "${btrfs_path}" | grep -c -i "${BASENAME}" || echo "0")
	done

	## Create a new read-only btrfs snapshot
	mkdir -p "${btrfs_path}/${btrfs_snap_dir}/${BASENAME}/${yymmdd}/"
	btrfs subvolume snapshot -r "${btrfs_path}" "${btrfs_path}/${btrfs_snap_dir}/${BASENAME}/${yymmdd}/${timestamp}" | tee -a "${logfile}"

done

# Echo line delimeter
echo -e "\n= = = = = "

echo -e "\n$(df -h -x tmpfs -x overlay -x devtmpfs -x efivarfs | column -t)\n" | tee -a "${logfile}"

echo -e "[$(date -R)] Ending Btrfs Snapshot Process\n" | tee -a "${logfile}"