incremental backup script for multiple computers and efficient use of disk space. Backups are based on a backup interval and no. of backups to keep.

rsync-backup.sh

#!/bin/bash

## incremental rsync backup script
## run hourly via cron, will take a back up every 24hrs for up to 7days.
## efficent use of space using hard links
## can handle computers been turned on / off
## executes n backup processes in parallel

# ------------- computers to backup -----------------------------------
# IP Address or fully qualified names here + remote backup directory
LOCATION=(
	location1:/home
	location2:/
	location3:/
	location4:/var/www
)

# ------------- backup interval in hours ------------------------------
BACKUP_INTERVAL=24

# ------------- number backups to keep --------------------------------
BACKUP_NO=14

# ------------- directory to save backups -----------------------------
SNAPSHOT_DIR=/tank/backups

# ------------- excludes ----------------------------------------------
EXCLUDES=(
	dev
	proc
	sys
	tmp
	[cC]ache
	.gvfs
)

# ------------ No. parallel jobs to execute ---------------------------
MAX_JOBS=2

# ---------------------------------------------------------------------
# ---------------------------  script  --------------------------------
# ---------------------------------------------------------------------
# make sure we're running as root, if not exit
if (( `id -u` != 0 )); then { echo "`date "+%b %d %T"`: Sorry, must be root.  Exiting..."; exit; } fi

# if a backup process is already running, exit
lockdir=/tmp/rsync_backup.lock
if mkdir "$lockdir"; then
	# Remove lockdir when the script finishes, or when it receives a signal
	trap 'rm -rf "$lockdir"' 0	# remove directory when script finishes
	#trap "exit 2" 1 2 3 15		# terminate script when receiving signal
else
	echo "Cannot acquire lock (Already running).    exiting..."
	exit 0
fi

backup ()
(
	ADDRESS=${LOCATION//:*/}
	BACKUP_DIR=${LOCATION//*:/}

	# if backup directory already exists, continue ...
	if [ -d $SNAPSHOT_DIR/$ADDRESS ]; then

		# if last backup was greater that $BACKUP_INTERVAL hrs ago, continue...
		if test $(date -d "-$BACKUP_INTERVAL hours" +%s) -gt $(stat -c "%Y" $SNAPSHOT_DIR/$ADDRESS/backup.0); then

			ping -c 1 $ADDRESS > /dev/null
			if [ $? -eq 0 ]; then

				echo "`date "+%b %d %T"`: Begining backup for $ADDRESS."

				# delete the oldest snapshot, if it exists
				if [ -d $SNAPSHOT_DIR/$ADDRESS/backup.$BACKUP_NO ] ; then
					rm -rf $SNAPSHOT_DIR/$ADDRESS/backup.$BACKUP_NO
					mv $SNAPSHOT_DIR/$ADDRESS/backup.$(($BACKUP_NO-1)) $SNAPSHOT_DIR/$ADDRESS/backup.$BACKUP_NO
				fi

				# shift the middle snapshot(s) back by one, if they exist
				COUNT=$BACKUP_NO
				while [ $COUNT -gt 2 ]; do
					COUNT=$(($COUNT-1))
					if [ -d $SNAPSHOT_DIR/$ADDRESS/backup.$(($COUNT-1)) ] ; then
						mv $SNAPSHOT_DIR/$ADDRESS/backup.$(($COUNT-1)) $SNAPSHOT_DIR/$ADDRESS/backup.$COUNT
					fi
				done

				# make a hard-link-only (except for dirs) copy of the latest snapshot, if that exists
				if [ -d $SNAPSHOT_DIR/$ADDRESS/backup.0 ] ; then
					cp -al $SNAPSHOT_DIR/$ADDRESS/backup.0 $SNAPSHOT_DIR/$ADDRESS/backup.1
				fi

				# rsync from the system into the latest snapshot
				echo "Backing up $ADDRESS"
				rsync -qaAXEW `exclude` --delete --link-dest=$SNAPSHOT_DIR/$ADDRESS/backup.1 $ADDRESS:$BACKUP_DIR $SNAPSHOT_DIR/$ADDRESS/backup.0

				# update the mtime of backup dir to reflect the snapshot time
				touch $SNAPSHOT_DIR/$ADDRESS/backup.0
			else
				ELAPSED="$((($(date +%s) - $(stat -c "%Y" $SNAPSHOT_DIR/$ADDRESS/backup.0))/3600))hrs"
				echo "`date "+%b %d %T"`: $ADDRESS last backup $ELAPSED ago and has failed to respod to ping attempt "
			fi
		fi
	else
		# if backup directory does not already exist..
		ping -c 1 $ADDRESS > /dev/null
		if [ $? -eq 0 ]; then
			echo "`date "+%b %d %T"`: First backup for $ADDRESS"
			echo "Creating Backup Directory: $SNAPSHOT_DIR/$ADDRESS"
			mkdir -p $SNAPSHOT_DIR/$ADDRESS
			echo "Backing up $ADDRESS"
			rsync -qaAXEW --stats `exclude` $ADDRESS:$BACKUP_DIR $SNAPSHOT_DIR/$ADDRESS/backup.0
			touch $SNAPSHOT_DIR/$ADDRESS/backup.0
		else
			echo "`date "+%b %d %T"`: $ADDRESS hasn't been backed up yet and failed to respod to ping attempt "
		fi
	fi
)

exclude ()
{
	for E in ${EXCLUDES[*]}; do 
		echo -n "--exclude=$E "
	done
}

forky() {
	while [[ $(jobs | wc -l) -ge $MAX_JOBS ]] ; do
		sleep 10
	done
}

if [[ $MAX_JOBS -eq 1 ]]; then
	for LOCATION in ${LOCATION[*]}; do
		backup
	done
else
	for LOCATION in ${LOCATION[*]}; do
		backup &
		forky
	done
fi

wait

## Refrences...
## http://www.mikerubel.org/computers/rsync_snapshots/ by Mike Rubel.
## http://sourcebench.com/languages/bash/simple-parallel-processing-with-bash-using-wait-and-jobs/
## http://mywiki.wooledge.org/BashFAQ/045 ensure that only one instance of a script is running at a time.