#!/bin/bash
#
#  make_snapshot
#  Seann Herdejurgen
#  July, 2002
#
#  This script makes rotating backup-snapshots of $DIR to the directory
#  $SNAPSHOT.  This script is called with two parameters, the name of the
#  snapshot and the number of snapshots to keep.  You can use the following
#  crontab entries to keep 6 days of daily snapshots and 4 weeks of weekly
#  snapshots:
#
#     0 0 * * 0 /usr/local/sbin/make_snapshot weekly 4
#     0 0 * * 1-6 /usr/local/sbin/make_snapshot daily 6
#
#  If you use this script to mirror your entire hard drive, it may take
#  several hours.  If this is the case, it is recommended that you make
#  snapshots daily instead of hourly.
#
#  This script is based on an original script from Mike Rubel.
#
DIR=/
SNAPSHOT=/.snapshot

error() {
   echo "$0: $@" 1>&2
   exit 1
}

# Make sure we're running as root
if [ `id -u` != 0 ]; then error "You must be root to use this script"; fi

# Check command line parameters
if [ "$1" = "" -o "$2" = "" ]; then
   echo "usage: $0 <snapshot type> <max snapshots>"
   exit 1
fi

type=$1
(( max = $2 - 1 ))

# Remount the snapshot as read-write
mount -o remount,rw $SNAPSHOT || error "could not remount $SNAPSHOT read-write"

# Delete the oldest snapshot in the background
if [ -d $SNAPSHOT/${type}.${max} ]; then
   mv $SNAPSHOT/${type}.${max} $SNAPSHOT/.delete
   nice /bin/rm -rf $SNAPSHOT/.delete &
fi

# rsync source files into the latest snapshot (notice that rsync deletes/unlinks
tination file prior to writing the file if the file has changed)  This
# behavior is desired as it preserves the integrity of our other snapshot(s).
time rsync -va --delete --delete-excluded --exclude=/dev --exclude=/proc
--exclude=$SNAPSHOT $DIR
$SNAPSHOT/.latest

# Make the snapshot read-only
chmod a-w $SNAPSHOT/.latest

# Shift the middle snapshots(s) back by one, if they exist
while [ $max -ge 1 ]; do
   (( newer = max - 1 ))
   if [ -d $SNAPSHOT/${type}.${newer} ]; then
      mv $SNAPSHOT/${type}.${newer} $SNAPSHOT/${type}.${max}
   fi
   (( max = newer ))
done

# Update the mtime of ${type}.0 to reflect the snapshot time
mv $SNAPSHOT/.latest $SNAPSHOT/${type}.0
touch $SNAPSHOT/${type}.0

# Make a hard-link-only (except for dirs) copy of the latest snapshot
# to prepare for next snapshot.
nice cp -al $SNAPSHOT/${type}.0 $SNAPSHOT/.latest

# Wait for rm to finish if still running
wait

# Remount the snapshot as read-only
mount -o remount,ro $SNAPSHOT || error "could not remount $SNAPSHOT read-only"

# Informational only
echo ""
df -k
echo ""
ls -al $SNAPSHOT
echo ""
echo Finished `date`