Incremental backup to external drive using snapper and btrfs send/receive

backup

#!/bin/bash
# James W. Barnett

# Takes snapshots of each snapper configuration. It then sends the snapshot to
# a location on an external drive. After the initial transfer, it does
# incremental snapshots on later calls. It's important not to delete the
# snapshot created on your system since that will be used to determine the
# difference for the next incremental snapshot.

# Can set the backup directory here, or in the snapper configuration file with
# EXT_BACKUP_LOCATION
declare -r mybackupdir="/media/abma/backup"

# You can set a snapper configuration to be excluded by setting EXT_BACKUP="no"
# in its snapper configuration file.

#--------------------------------------------------------
# Don't modify anything below here

set -e

if [[ $EUID -ne 0 ]]; then
    echo "Script must be run as root." 
    exit
fi

declare -r description="latest incremental backup"

# It's important not to change this userdata in the snapshots, since that's how
# we find the previous one.
declare -r userdata="extbackup=yes"
declare -r configs=$(find /etc/snapper/configs/* -printf '%f\t')

for x in $configs; do
    unset EXT_BACKUP
    unset EXT_BACKUP_LOCATION
    source /etc/snapper/configs/$x
    do_backup=${EXT_BACKUP:-"yes"}

    if [[ $do_backup == "yes" ]]; then
	echo "Creating backup from $x"

        BACKUPDIR=${EXT_BACKUP_LOCATION:-"$mybackupdir"}

        if [[ -z $BACKUPDIR ]]; then
            echo "ERROR: External backup location not set!"
            exit 1
        elif [[ ! -d $BACKUPDIR ]]; then
            echo "ERROR: $BACKUPDIR is not a directory."
            exit 1
        fi
        old_number=$(snapper -c $x list -t single | awk '/'"$userdata"'/ {print $1}')
        new_number="$(snapper -c $x create --print-number)"
        sync
       
        new_snapshot=$SUBVOLUME/.snapshots/$new_number/snapshot
        new_info=$SUBVOLUME/.snapshots/$new_number/info.xml
        backup_location=$BACKUPDIR/$x/$new_number/
        old_backup=$BACKUPDIR/$x/$old_number/snapshot

        mkdir -p $backup_location

        if [[ -z "$old_number" ]]; then

            echo "Performing initial backup for snapper configuration '$x'. This could take awhile..."
            btrfs send $new_snapshot | btrfs receive $backup_location

        else

            old_snapshot=$SUBVOLUME/.snapshots/$old_number/snapshot

            # Sends the difference between the new snapshot and old snapshot to
            # the backup location. Using the -c flag instead of -p tells it that
            # there is an identical subvolume to the old snapshot at the
            # receiving location where it can get its data. This helps speed up
            # the transfer.

            btrfs send -c $old_snapshot $new_snapshot | btrfs receive $backup_location

            cp $new_info $backup_location
            snapper -c $x delete $old_number

        fi

        # Tag new snapshot as the latest
        snapper -v -c $x modify -d "$description" -u "$userdata" $new_number 

    fi

done

date > $HOME/.lastbackup