Incremental backup using btrfs snapshot

backup.sh

#!/usr/bin/env bash

DEVICE=UUID="2b387045-9c35-4da0-8ed2-79014eb85040"
BACKUP_DEVICE="dde"
BACKUP_MOUNT="/mnt"
DEST="$BACKUP_MOUNT/backup"
MAX_BACKUPS=20

SOURCE="/home/yann"
SNAP_DIR="/home/backup"

_mount() {
    cryptsetup luksOpen "$DEVICE" "$BACKUP_DEVICE"
    mount "/dev/mapper/$BACKUP_DEVICE" "$BACKUP_MOUNT"
}

_umount() {
    sync
    umount "/dev/mapper/$BACKUP_DEVICE"
    cryptsetup luksClose "$BACKUP_DEVICE"
}

_backup() {
    latest="$(btrfs subvolume list -ors --sort=gen "$SNAP_DIR" | rev | cut -d"/" -f1 | rev | tail -1)"
    if [[ -z "$latest" ]]; then
        date=$(date "+%Y-%m-%dT%H:%M:%S")
        latest="$date-$(uuidgen)"
        btrfs subvolume snapshot -r "$SOURCE" "$SNAP_DIR/$latest"
        btrfs send "$SNAP_DIR/$latest" | btrfs receive "$DEST/"
    else
        date=$(date "+%Y-%m-%dT%H:%M:%S")
        new_latest="$date-$(uuidgen)"
        btrfs subvolume snapshot -r "$SOURCE" "$SNAP_DIR/$new_latest"
        btrfs send -p "$SNAP_DIR/$latest" "$SNAP_DIR/$new_latest" | btrfs receive "$DEST/"
    fi
}

_clean() {
    todelete="$(btrfs subvolume list -ors --sort=gen "$SNAP_DIR" | rev | cut -d"/" -f1 | rev | head -n -$MAX_BACKUPS)"
    for vol in $todelete; do
        btrfs subvolume delete "$SNAP_DIR/$vol";
    done

    todelete="$(btrfs subvolume list -ors --sort=gen "$DEST" | rev | cut -d"/" -f1 | rev | head -n -$MAX_BACKUPS)"
    for vol in $todelete; do
        btrfs subvolume delete "$DEST/$vol";
    done
}

_get() {
    local_latest="$(btrfs subvolume list -ors --sort=gen "$SNAP_DIR" | rev | cut -d"/" -f1 | rev | tail -1)"
    echo "Local last: $local_latest"

    latest="$(btrfs subvolume list -ors --sort=gen "$DEST" | rev | cut -d"/" -f1 | rev | tail -1)"
    echo "Last: $latest"

    # retrieve backup
    btrfs send -p "$DEST/$local_latest" "$DEST/$latest" | btrfs receive "$SNAP_DIR/"

    # custom
    umount /home/yann/.cache

    # Apply backup on $SOURCE
    btrfs subvolume delete "$SOURCE"
    btrfs subvolume snapshot "$SNAP_DIR/$latest" "$SOURCE"

    # custom
    mount -a
}

case "$1" in
    mount) shift;         _mount "$@" ;;
    umount) shift;        _umount "$@" ;;
    backup) shift;        _backup "$@" ;;
    clean) shift;         _clean "$@" ;;
    get) shift;           _get "$@" ;;
esac
exit 0