Rotating Backups

gistfile1.sh

#!/bin/bash

unset PATH;

# $1 = path to backup
# $2 = name of backup folder

# ------------- system commands used by this script --------------------
ID=/usr/bin/id;
ECHO=/bin/echo;

MOUNT=/bin/mount;
RM=/bin/rm;
MV=/bin/mv;
CP=/bin/cp;
TOUCH=/bin/touch;

RSYNC=/usr/bin/rsync;

# ------------- file locations -----------------------------------------

MOUNT_DEVICE=/dev/sdc1;
SNAPSHOT_RW=/mnt/back1;
EXCLUDES=/root/backup_excludes.txt;

BACKUP_COUNT=100;
BACKUP_NAME=backup;

# ------------- the script itself --------------------------------------

# make sure we're running as root
if (( `$ID -u` != 0 )); then
$ECHO "Sorry, must be root.  Exiting..."; exit;
fi

# attempt to remount the RW mount point as RW; else abort
$MOUNT -o remount,rw $MOUNT_DEVICE $SNAPSHOT_RW ;
if (( $? )); then
	$ECHO "snapshot: could not remount $SNAPSHOT_RW readwrite";
	exit;
fi;

# step 1: delete the oldest snapshot, if it exists:
if [ -d $SNAPSHOT_RW/$2/$BACKUP_NAME.$BACKUP_COUNT ] ; then
	$RM -rf $SNAPSHOT_RW/$2/$BACKUP_NAME.$BACKUP_COUNT ;
fi ;

# step 2: shift the middle snapshots(s) back by one, if they exist
for (( i = $BACKUP_COUNT; i >= 1 ; i-- ))
do
	if [ -d $SNAPSHOT_RW/$2/$BACKUP_NAME.$(($i-1)) ] ; then
		$MV $SNAPSHOT_RW/$2/$BACKUP_NAME.$(($i-1)) $SNAPSHOT_RW/$2/$BACKUP_NAME.$i;
	fi;
done

# step 3: rsync from the system into the latest snapshot (notice that
# rsync behaves like cp --remove-destination by default, so the destination
# is unlinked first.  If it were not so, this would copy over the other
# snapshot(s) too!
$RSYNC -va --delete --delete-excluded --exclude-from="$EXCLUDES" --link-dest=$SNAPSHOT_RW/$2/$BACKUP_NAME.1 $1 $SNAPSHOT_RW/$2/$BACKUP_NAME.0;

# step 4: update the mtime of $BACKUP_NAME.0 to reflect the snapshot time
$TOUCH $SNAPSHOT_RW/$2/$BACKUP_NAME.0 ;

# now remount the RW snapshot mountpoint as readonly
$MOUNT -o remount,ro $MOUNT_DEVICE $SNAPSHOT_RW ;
if (( $? )); then
	$ECHO "snapshot: could not remount $SNAPSHOT_RW readonly";
	exit;
fi;