Linux dash script to perform incremental backups using rsync

backup.sh

#!/bin/dash

# A script to perform incremental backups using rsync and a backup device
#
# Usage:
#   - Place this script into /usr/local/sbin/
#   - Adapt BACKUP_DEVICE variable to your backup device
#   - Setup backup.sh as a automated job/task:
#       - If you have a desktop that is not turned on all the time
#         it is recommended to use anacron instead of cron.
#
#         This is done by adding the following entry to /etc/anacrontab:
#         "1	10	example.daily	/usr/local/sbin/backup.sh > /var/log/backup.log"
#         Also see: https://www.tecmint.com/cron-vs-anacron-schedule-jobs-using-anacron-on-linux/
#
# Notes:
#   - This script is an adaption of the example from
#     https://linuxconfig.org/how-to-create-incremental-backups-using-rsync-on-linux
#   - Use duplicity if you want to backup in the network

# -e:   exit on command fail
# -u:   treat unset variables as an error
# -x:   option causes bash to print each command before executing it. For debugging.
set -eux


readonly BACKUP_DEVICE="/dev/sdb1"
readonly SOURCE_DIR="/home/"
readonly BACKUP_DIR="/media/BACKUP"
readonly DATETIME="$(date '+%Y-%m-%d_%H:%M:%S')"
readonly BACKUP_PATH="${BACKUP_DIR}/${DATETIME}"
readonly LATEST_LINK="${BACKUP_DIR}/latest"


################### MAIN ###################
main() {
    trap cleanup_error INT QUIT TERM
    trap cleanup       EXIT

    if ! isPathMounted "${BACKUP_DIR}"; then
        if [ ! -d "${BACKUP_DIR}" ]; then
            mkdir "${BACKUP_DIR}"
        fi
        mount "${BACKUP_DEVICE}" "${BACKUP_DIR}"
        if [ ! -d "${LATEST_LINK}" ]; then
            mkdir "${LATEST_LINK}"
        fi
    fi

    if isPathMounted "${BACKUP_DIR}"; then
        echo "backing up ${SOURCE_DIR} into ${BACKUP_DIR}..."
        ################### BACKUP BY USING RSYNC ###################
        # -a:   archive - preserves the most important attributes of the source files
        # -t:   preserve time
        # -v:   verbose output
        # --delete:         files deleted from source are also deleted on destination
        # --protect-args:   no space-splitting; wildcard chars only
        # --progress:       shows progress during transfer
        rsync --archive      \
              --verbose      \
              -t             \
              --delete       \
              --progress     \
              --checksum     \
              --backup       \
              --protect-args \
              --link-dest "${LATEST_LINK}"    \
              --exclude="Downloads/"          \
              --exclude=".local/share/Trash/" \
              --exclude=".cache/"             \
              "${SOURCE_DIR}"                 \
              "${BACKUP_PATH}"
        # feedback to the user
        EXIT_STATUS=$?
        if [ ${EXIT_STATUS} -eq 0 -o ${EXIT_STATUS} -eq 24 ]; then
            echo "BACKUP done successfully! =)"
            # update the link to the latest backup
            rm "${LATEST_LINK}"  # delete the link but keep the backup
            cd "${BACKUP_DIR}"
            ln -s "${DATETIME}" "${LATEST_LINK}"
            cd ~
        else
            echo "BACKUP aborted with error code ${EXIT_STATUS}"
        fi
    fi
}


################### CHECK MOUNT ###################
# Checks whether path or device is mounted
# where: -r = --raw, -n = --noheadings, -o = --output
# returns: 0 = found, 1 = not found
isMounted     () { findmnt -rno SOURCE,TARGET "$1" >/dev/null; }  # path or device
isDevMounted  () { findmnt -rno SOURCE        "$1" >/dev/null; }  # device only
isPathMounted () { findmnt -rno        TARGET "$1" >/dev/null; }  # path only


################### WAITING UMOUNT ###################
# Tries to umount with a retry-time of 10s until it was successful
waiting_umount() {
    echo "unmounting $1..."
    busy=true
    while $busy; do
        if isPathMounted "$1"; then
            umount "$1"
            EXIT_STATUS=$?
            if [ $EXIT_STATUS -eq 0 ]; then
                busy=false  # umount successful
                echo "unmounting successfully!"
            else
                echo -n '.'  # output to show that the script is alive
                sleep 10
            fi
        else
            busy=false  # not mounted
        fi
    done
}


################### FINALLY ###################

cleanup_error() {
    # unset traps
    trap - INT QUIT TERM
    # feedback to the user
    echo "BACKUP finished with status: $?"
    # remove the faulty backup
    if [ -d "${BACKUP_PATH}" ]; then
        rm -rf "${BACKUP_PATH}"
    fi
}


cleanup() {
    # unset traps
    trap - EXIT
    # script cleanup here
    waiting_umount "${BACKUP_DIR}"
    if [ -d "${BACKUP_DIR}" ]; then
        rmdir "${BACKUP_DIR}"
    fi
}


main "$@"