sysrescue-customize

#! /usr/bin/env bash
#
# sysrescue-customize - customize an existing SystemRescue iso image
# 
# Author: Gerd v. Egidy
# SPDX-License-Identifier: GPL-3.0-or-later
#
# see https://www.system-rescue.org/scripts/sysrescue-customize/ for details

# bash-checks right at the top due to many bashisms in the rest of the script
if [ -n "$POSIXLY_CORRECT" ] || [ -z "$BASH_VERSION" ]; then
    echo "ERROR: bash >= 4.0 is required for this script."
    exit 1
fi

if (( BASH_VERSINFO[0]*100 + BASH_VERSINFO[1] < 400 )); then
    echo "ERROR: bash >= 4.0 is required for this script."
    exit 1
fi

# abort on failures
set -o errexit -o pipefail -o noclobber -o nounset

# we expect the isohybrid-mbr file to be within the iso image at this path
# xorriso doesn't require the file to be in the iso filesystem, but SystemRescue always provides it, so we can rely on it
ISOHYBRID_MBR="isolinux/isohdpfx.bin"

print_help()
{
    echo "sysrescue-customize - customize an existing SystemRescue iso image"
    echo ""
    echo "Usage in unpack mode:"
    echo "sysrescue-customize --unpack -s|--source=<ISO-FILE> -d|--dest=<DIR>"
    echo "    [-o|--overwrite] [-v|--verbose]"
    echo ""
    echo "Usage in rebuild mode:"
    echo "sysrescue-customize --rebuild -s|--source=<DIR> -d|--dest=<ISO-FILE>"
    echo "    [-m|--srm-dir=<DIR>] [-o|--overwrite] [-v|--verbose]"
    echo ""
    echo "Usage in auto-mode:"
    echo "sysrescue-customize --auto -s|--source=<ISO-FILE> -d|--dest=<ISO-FILE>"
    echo "    -r|--recipe-dir=<DIR> [-w|--work-dir=<DIR>] [-o|--overwrite] [-v|--verbose]"
    echo ""
    echo "--source=<ISO or DIR>       unpack and auto: iso file (or raw block device)"
    echo "                                     to extract. Must be in iso9660 format."
    echo "                                     On SystemRescue: can be omitted, then"
    echo "                                     the boot device is used if possible."
    echo "                            rebuild: source dir to rebuild the iso image from."
    echo "                                     Must be in the same format as created by"
    echo "                                     --unpack."
    echo "--dest=<ISO or DIR>         unpack: destination directory to unpack into."
    echo "                            rebuild and auto: destination for the iso file."
    echo "--srm-dir=<DIR>             Content of the directory will be packed into a" 
    echo "                            SystemRescueModule (SRM). The --source dir will"
    echo "                            be modified when this option is used."
    echo "--recipe-dir=<DIR>          Directory that contains a recipe for fully"
    echo "                            automatic customization. Uses these subdirectories:"
    echo "                            iso_delete (Step 1: files there trigger deletes)"
    echo "                            iso_add  (Step 2: add or overwrite)"
    echo "                            iso_patch_and_script (Step 3: patch -p1 or scripts)"
    echo "                            build_into_srm (Step 4: like --srm-dir option)"
    echo "                            See SystemRescue manual for more details."
    echo "--work-dir=<DIR>            Use this as a temporary work directory for"
    echo "                            unpacking and rebuilding."
    echo "--overwrite                 Without this option the target directories or"
    echo "                            files must be empty or non-existing. This option"
    echo "                            will overwrite existing files without questions."
    echo "--verbose                   Verbose output when running xorriso."
    echo ""
    echo "See https://www.system-rescue.org/scripts/sysrescue-customize/ for details."
    
    return
}

# when running on SystemRescue:
# check if we can use the boot device as source dir
sysrescue_bootmnt_source()
{
    # are we on SystemRescue?
    if ! grep -q "ID=sysrescue" /etc/os-release 2>/dev/null; then
        echo "ERROR: source option missing or empty (not running on SystemRescue)"
        exit 1
    fi
    
    # check where bootmnt is mounted from
    local bootmnt_src
    local RET=0
    bootmnt_src=$(findmnt --mountpoint /run/archiso/bootmnt --output source --raw --noheadings) || RET=$?
    
    if [[ $RET -ne 0 ]] || [[ ! -b "${bootmnt_src}" ]] || ! blkid "${bootmnt_src}" | grep -q "TYPE=\"iso9660\""; then
        echo "ERROR: bootmnt source not in iso format, specify a source manually"
        exit 1
    fi
    
    # we have some kind of iso block device as bootmnt
    # we could have a isohybrid on a regular disk, that would result in a partition instead of the root
    
    local deviceno=$(stat --format="%Hr:%Lr" "${bootmnt_src}")
    if [[ -e "/sys/dev/block/${deviceno}/partition" ]]; then
        # we have a partition, we need to get the corresponding main device
        deviceno=$(stat --format="%Hr:0" "${bootmnt_src}")
    fi

    # navigate from the /sys entry to the entry in /dev
    if [[ ! -d "/sys/dev/block/${deviceno}/device/block" ]]; then
        echo "ERROR: can't find bootmnt source, specify a source manually"
        exit 1
    fi

    local devname=$(ls -1 "/sys/dev/block/${deviceno}/device/block")
    
    if [[ -z "${devname}" ]] || [[ ! -b "/dev/${devname}" ]]; then
        echo "ERROR: can't find bootmnt source, specify a source manually"
        exit 1
    fi
    
    # success, we have a source we can use
    SOURCE="/dev/${devname}"

    return
}

# error while parsing commandline parameters
argument_error()
{
    echo "$1"
    echo
    echo "---------------------------------"
    echo
    print_help
    exit 2
}

parse_args()
{
    # adapted from https://stackoverflow.com/a/29754866 by Robert Siemer
    # version edited Mar 4 '21 at 0:11, licensed under CC BY-SA 4.0 due to Stackoverflow Terms of Service
    # https://creativecommons.org/licenses/by-sa/4.0/

    # show help when no arguments given
    [[ $# -eq 0 ]] && { print_help ; exit 0 ; }
    
    # -allow a command to fail with !’s side effect on errexit
    # -use return value from ${PIPESTATUS[0]}, because ! hosed $?
    ! getopt --test > /dev/null 
    if [[ ${PIPESTATUS[0]} -ne 4 ]]; then
        echo 'ERROR: `getopt --test` failed in this environment'
        exit 1
    fi

    local OPTIONS="s:d:m:r:w:ovh"
    local LONGOPTS="unpack,rebuild,auto,source:,dest:,srm-dir:,recipe-dir:,work-dir:,overwrite,verbose,help"

    # option variables as globals, set to default values
    declare -g MODE=""
    declare -g SOURCE=""
    declare -g DEST=""
    declare -g SRM_DIR=""
    declare -g WORK_DIR=""
    declare -g RECIPE_DIR=""
    declare -g OVERWRITE=0
    declare -g VERBOSE=""
    
    # -regarding ! and PIPESTATUS see above
    # -temporarily store output to be able to check for errors
    # -activate quoting/enhanced mode (e.g. by writing out “--options”)
    # -pass arguments only via   -- "$@"   to separate them correctly
    ! PARSED=$(getopt --options=$OPTIONS --longoptions=$LONGOPTS --name "$0" -- "$@")
    if [[ ${PIPESTATUS[0]} -ne 0 ]]; then
        # e.g. return value is 1
        #  then getopt has complained about wrong arguments to stdout
        echo
        print_help
        exit 2
    fi
    # read getopt’s output this way to handle the quoting right:
    eval set -- "$PARSED"

    while true; do
        case "$1" in
            --unpack)
                [[ ! -z "$MODE" ]] && argument_error "ERROR: mode conflict"
                MODE="unpack"
                shift
                ;;
            --rebuild)
                [[ ! -z "$MODE" ]] && argument_error "ERROR: mode conflict"
                MODE="rebuild"
                shift
                ;;
            --auto)
                [[ ! -z "$MODE" ]] && argument_error "ERROR: mode conflict"
                MODE="auto"
                shift
                ;;
            -s|--source)
                SOURCE="$2"
                shift 2
                ;;
            -d|--dest)
                DEST="$2"
                shift 2
                ;;
            -m|--srm-dir)
                SRM_DIR="$2"
                shift 2
                ;;
            -w|--work-dir)
                WORK_DIR="$2"
                shift 2
                ;;
            -r|--recipe-dir)
                RECIPE_DIR="$2"
                shift 2
                ;;
            -o|--overwrite)
                OVERWRITE=1
                shift
                ;;
            -v|--verbose)
                VERBOSE="-report_about ALL"
                shift
                ;;
            -h|--help)
                print_help
                exit 0
                ;;
            --)
                shift
                break
                ;;
            *)
                echo "ERROR: Argument parsing logic bug"
                exit 2
                ;;
        esac
    done

    # we want no positional arguments 
    [[ $# -ne 0 ]] && argument_error "ERROR: positional arguments not allowed"
    
    [[ -z "$MODE" ]] && argument_error "ERROR: mode option missing"
    [[ -z "$DEST" ]] && argument_error "ERROR: dest option missing or empty"

    if [[ -z "$SOURCE" ]]; then
        sysrescue_bootmnt_source
    fi
    
    if [[ $MODE == "unpack" ]] ; then
        [[ ! -z "$RECIPE_DIR" ]] && argument_error "ERROR: option recipe-dir not allowed in unpack mode"
        [[ ! -z "$WORK_DIR" ]] && argument_error "ERROR: option work-dir not allowed in unpack mode"
        [[ ! -z "$SRM_DIR" ]] && argument_error "ERROR: option srm-dir not allowed in unpack mode"
    fi
    if [[ $MODE == "rebuild" ]] ; then
        [[ ! -z "$RECIPE_DIR" ]] && argument_error "ERROR: option recipe-dir not allowed in rebuild mode"
        [[ ! -z "$WORK_DIR" ]] && argument_error "ERROR: option work-dir not allowed in rebuild mode"
    fi
    if [[ $MODE == "auto" ]] ; then
        [[ ! -z "$SRM_DIR" ]] && argument_error "ERROR: option srm-dir not allowed in auto mode"
        [[ ! -z "$RECIPE_DIR" ]] || argument_error "ERROR: recipe-dir option missing or empty"
    fi
    
    return
}

# ensure we have all the programs we need
bin_check()
{
    declare -a missing=()
    declare -a bins
    bins=(
        cat dirname find getopt grep ls mkdir mksquashfs mktemp patch realpath rm rsync sed sort tr xorriso
    )
    # ignore findmnt, blkid, stat: they are only used when ensured we are on SystemRescue
    
    for bin in "${bins[@]}"; do
        if ! type "$bin" >/dev/null 2>&1; then
            missing+=("$bin")
        fi
    done
    
    if (( ${#missing[@]} )); then
        echo "ERROR: required binaries missing: ${missing[*]}"
        echo "Please install them using the package manager of your distribution"
        exit 1
    fi

    if ! xorriso -help >/dev/null 2>&1; then
        echo "Error running xorriso"
        echo "Please ensure that xorriso is installed correctly."
        exit 1
    fi

    # check that xorriso supports the -drive_access option
    if ! xorriso -help 2>&1 | grep "drive_access" >/dev/null; then
        echo "xorriso seems to not support the -drive_access option"
        echo "Please check the installed version of xorriso. Version 1.5.2 or newer is required."
        exit 1
    fi
    
    return
}

write_iso_checks()
{
    local SOURCE_DIR="$1"
    local DEST_ISO="$2"

    # verify parameters and environment
    
    if ! [[ -f "${SOURCE_DIR}/meta-pvd" ]] || ! [[ -f "${SOURCE_DIR}/meta-cmd" ]] || ! [[ -d "${SOURCE_DIR}/filesystem/" ]]; then
        echo "ERROR: source dir not in the expected format"
        exit 3
    fi
    
    if ! [[ -f "${SOURCE_DIR}/filesystem/${ISOHYBRID_MBR}" ]]; then
        echo "ERROR: isohybrid-mbr file missing in filesystem (${ISOHYBRID_MBR})"
        exit 3
    fi

    if [[ -e "${DEST_ISO}" ]] && [[ ! -f "${DEST_ISO}" ]]; then
        echo "ERROR: iso destination not a file"
        exit 3
    fi
    
    if [[ -e "${DEST_ISO}" ]]; then
        if [[ $OVERWRITE -eq 1 ]]; then
            rm -f "${DEST_ISO}"
        else
            echo "ERROR: target iso file already existing (you may want to use --overwrite)"
            exit 3
        fi
    fi

    if ! grep -q "^Publisher Id *: " "${SOURCE_DIR}/meta-pvd"; then 
        echo "ERROR: meta-pvd missing necessary information or wrong format"
        exit 3
    fi

    if ! grep -q "^-volid" "${SOURCE_DIR}/meta-cmd" || \
       ! grep -q "^-boot_image" "${SOURCE_DIR}/meta-cmd" ; then
        echo "ERROR: meta-cmd missing necessary information or wrong format"
        exit 3
    fi

    # forbid " and \ in meta-cmd as it means very complex quoting, we don't support that
    if grep -q "\\\\" "${SOURCE_DIR}/meta-cmd" || \
       grep -q "\"" "${SOURCE_DIR}/meta-cmd"; then
        echo "ERROR: illegal char in meta-cmd"
        exit 3
    fi
    
    return
}

# write_iso_checks() is expected to have succeeded before
write_iso()
{
    local SOURCE_DIR="$1"
    local DEST_ISO="$2"

    local PUBLISHER=$(grep "^Publisher Id *: " "${SOURCE_DIR}/meta-pvd" | sed -e "s/^Publisher Id *: //")
    local APP_ID=$(grep "^App Id *: " "${SOURCE_DIR}/meta-pvd" | sed -e "s/^App Id *: //")

    # read commands from meta-cmd file into array, split on space
    # remove the lines with "-volume_date" and "-boot_image isolinux system_area"
    # we want the current volume_date be set
    # we explicitly supply the isohybrid-file because we don't want xorriso having it to extract it from the original file
    # there is no way to write it out during the read phase, so the write phase would need to read from the original iso file which 
    # would create unexpected dependencies and complications, so using the path hardcoded in $ISOHYBRID_MBR is the way
    declare -a XO_PARAMETERS_RAW

    # needs || true because it always returns nonzero
    read -r -a XO_PARAMETERS_RAW -d "" < <(cat "${SOURCE_DIR}/meta-cmd" | grep -v -E "^(-volume_date|-boot_image isolinux system_area)" ) || true
   
    # we now have to sanitize the parameter array: remove single quotes and reconnect the parameters split by spaces within the quotes
    # we don't want to eval the parameters, because reading from a malicious iso image could trigger code execution
    # example patterns of what we have to deal with:
    # -volid 'RESCUE807'
    # -volid 'RESCUE 807'
    # -volid 'RESCUE 8 07'
    # bin_path='/isolinux/isolinux.bin'
    
    # relies on " and \ being forbidden, see check in write_iso_checks()

    declare -a XO_PARAMETERS
    local quote_status=0
    local quoted_var
    for i in "${XO_PARAMETERS_RAW[@]}" ; do

        if [[ $quote_status -eq 1 ]]; then
            if [[ "${i}" = *\'* ]]; then
                # end of the quote
                quoted_var="${quoted_var} ${i//\'/}"
                XO_PARAMETERS+=("${quoted_var}")
                quote_status=0
            else
                # more spaces, quoted section continues
                quoted_var="${quoted_var} ${i}"
            fi
        else
            if [[ "${i}" = *\'* ]]; then
                # beginning of a quoted section
                quoted_var="${i/\'/}"
                
                # does the quoted section end in the same array var again?
                if [[ "${quoted_var}" = *\'* ]]; then
                    # just remove all quotes and don't continue to the next array var
                    XO_PARAMETERS+=("${quoted_var//\'/}")
                else
                    # the quote continues to the next array var
                    quote_status=1
                fi
            else
                # no quote, pass variable unchanged
                XO_PARAMETERS+=("${i}")
            fi
        fi
    done

    # build the iso file
    xorriso -x\
            -compliance iso_9660_level=3 \
            -application_id "${APP_ID}" \
            -publisher "${PUBLISHER}" \
            -preparer_id "prepared by sysrescue-customize" \
            -boot_image isolinux system_area="${SOURCE_DIR}/filesystem/${ISOHYBRID_MBR}" \
            "${XO_PARAMETERS[@]}" \
            -outdev "${DEST_ISO}" \
            $VERBOSE \
            -map "${SOURCE_DIR}/filesystem/" "/"
            
    return
}

read_iso()
{
    local SOURCE_ISO="$1"
    local DEST_DIR="$2"

    # verify parameters and environment

    if [[ ! -e "${SOURCE_ISO}" ]]; then
        echo "ERROR: source iso not found"
        exit 3
    fi

    # do we have a block device as source? xorriso may need to be convinced to use it
    if [[ -b "${SOURCE_ISO}" ]]; then
        SOURCE_ISO="stdio:${SOURCE_ISO}"
    fi

    if [[ "${DEST_DIR}" == "/" ]]; then
        echo "ERROR: invalid destination dir"
        exit 3
    fi

    # check if we really have an iso file as source and not something else
    if ! xorriso -drive_access "shared:readonly" -indev "${SOURCE_ISO}" -toc >/dev/null 2>&1 ||
        xorriso -drive_access "shared:readonly" -indev "${SOURCE_ISO}" -toc 2>&1 | grep -E "(is blank|Drive address .* rejected)"; then
        echo "ERROR: source is not a valid ISO file"
        exit 3
    fi
    
    # we need an empty target dir
    if ( [[ -e "${DEST_DIR}" ]] && ! [[ -d "${DEST_DIR}" ]] ) || \
       ( [[ -d "${DEST_DIR}" ]] && ! $(find "${DEST_DIR}" -maxdepth 0 -empty -exec echo 1 \; | grep -q 1) );  then
        if [[ $OVERWRITE -eq 1 ]]; then
            rm -rf "${DEST_DIR}"
        else
            echo "ERROR: target directory already existing and not empty (you may want to use --overwrite)"
            exit 3
        fi
    fi
    
    # create target dir if it doesn't exist
    if ! [[ -d "${DEST_DIR}" ]]; then
        mkdir -p "${DEST_DIR}"
    fi
    mkdir -p "${DEST_DIR}/filesystem"

    xorriso -drive_access "shared:readonly" -indev "${SOURCE_ISO}" -report_system_area cmd $VERBOSE >"${DEST_DIR}/meta-cmd"
    xorriso -drive_access "shared:readonly" -indev "${SOURCE_ISO}" -pvd_info $VERBOSE >"${DEST_DIR}/meta-pvd"
    xorriso -osirrox on -drive_access "shared:readonly" -indev "${SOURCE_ISO}" -extract / "${DEST_DIR}/filesystem" $VERBOSE
    
    return
}

create_srm()
{
    local SRM_DIR="$1"
    local DEST_SRM="$2"

    # verify parameters and environment

    if [[ ! -d "${SRM_DIR}" ]]; then
        echo "ERROR: srm-dir not found"
        exit 3
    fi

    if [[ -e "${DEST_SRM}" ]] && [[ ! -f "${DEST_SRM}" ]]; then
        echo "ERROR: SRM destination not a file"
        exit 3
    fi
    
    if [[ -e "${DEST_SRM}" ]]; then
        # we explicitly say that creating SRMs will modify the rebuild source-dir
        # that also includes deleting/overwriting existing SRMs there
        # so don't require the --overwrite flag here
        rm -f "${DEST_SRM}" 
    fi
    
    # is the srm-dir empty?
    # test after deleting, so an empty source dir will yield no SRM even if one was there before
    if $(find "${SRM_DIR}" -maxdepth 0 -empty -exec echo 1 \; | grep -q 1);  then
        # don't create an empty SRM, ignore the whole call instead
        return
    fi

    local DEST_DIR=$(dirname "${DEST_SRM}")
    if [[ ! -d "${DEST_DIR}" ]]; then
        mkdir -p "${DEST_DIR}"
    fi

    local squashfs_options=""
    local squashfs_exclude=""

    # did the user specify a "pseudo-file"? a list with mode, uid, gid etc. overrides for files
    if [[ -f "${SRM_DIR}/.squashfs-pseudo" ]]; then
        squashfs_options+=" -pf \"${SRM_DIR}/.squashfs-pseudo\" "

        # exclude the pseudeo file from the filesystem
        squashfs_exclude+=" -e .squashfs-pseudo"
    fi
    
    # load options for the mksquashfs call from options file
    if [[ -f "${SRM_DIR}/.squashfs-options" ]]; then
        # strip comment lines, replace newlines with spaces to allow using multiple lines easily
        squashfs_options+=$(cat "${SRM_DIR}/.squashfs-options" | grep -v "^#" | tr '\n' ' ')

        # exclude the options file from the filesystem
        squashfs_exclude+=" -e .squashfs-options"
    fi

    # excludes must come after all other options
    squashfs_options+="$squashfs_exclude"
    
    # prepare the directory options to be correctly quoted for eval
    local dir_options="\"${SRM_DIR}\" \"${DEST_SRM}\""
    
    # eval the command to allow full parameter quoting and variable expansion in .squashfs-options file
    # this means the file must be fully trusted, it can easily execute arbitrary commands
    eval mksquashfs $dir_options -info -comp zstd -exit-on-error $squashfs_options

    return
}

set_loadsrm_option()
{
    local DEST_YAML="$1"
    
    if [[ -e "${DEST_YAML}" ]] && [[ ! -f "${DEST_YAML}" ]]; then
        echo "ERROR: config YAML destination not a file"
        exit 3
    fi
    
    if [[ -e "${DEST_YAML}" ]]; then
        # we explicitly say that creating SRMs will modify the rebuild source-dir
        # that also includes deleting/overwriting existing YAMLs there
        # so don't require the --overwrite flag here
        rm -f "${DEST_YAML}" 
    fi
    
    local DEST_DIR=$(dirname "${DEST_YAML}")
    if [[ ! -d "${DEST_DIR}" ]]; then
        mkdir -p "${DEST_DIR}"
    fi

    echo "---" >"${DEST_YAML}"
    echo "global:" >>"${DEST_YAML}"
    echo "    loadsrm: true" >>"${DEST_YAML}"
    
    return
}

# check the recipes before beginning to do anything
recipe_checks()
{
    local RECIPE_DIR="$1"

    if [[ ! -d "${RECIPE_DIR}" ]]; then
        echo "ERROR: recipe dir not existing"
        exit 3
    fi
    
    local DELETE_ROOT="${RECIPE_DIR}/iso_delete"
    local ADD_ROOT="${RECIPE_DIR}/iso_add"
    local CHANGE_SCRIPTS="${RECIPE_DIR}/iso_patch_and_script"
    local SRM_DIR="${RECIPE_DIR}/build_into_srm"
    
    if [[ ! -d "${DELETE_ROOT}" ]] && [[ ! -d "${ADD_ROOT}" ]] && \
       [[ ! -d "${CHANGE_SCRIPTS}" ]] && [[ ! -d "${SRM_DIR}" ]]; then
        echo "ERROR: no recipes in recipe-dir, no point in customizing anything"
        exit 3
    fi

    if [[ -d "${CHANGE_SCRIPTS}" ]]; then
        # make sure only sane filenames are used for the scripts and patches
        # this ensures that they are all executed in a repeatable and predicatable order, regardless of filesystem or OS
        # be really strict about this
        local illegal_names=$(ls -1 "${CHANGE_SCRIPTS}" | grep -v -E "^[0-9_a-z-]+$" | grep -v -E "^[0-9_a-z-]+\.patch$")
        if [[ ! -z "$illegal_names" ]]; then
            echo "ERROR: illegal change script or patch filename: $illegal_names"
            echo "only 0-9 a-z _ - are allowed in filenames, patches must end in \".patch\""
            exit 3
        fi
        
        if find "${CHANGE_SCRIPTS}" -mindepth 1 -type d | grep -q "." ; then
            echo "ERROR: illegal subdirectory in patch_and_script directory"
            exit 3
        fi
    
        local SCRIPT
        for SCRIPT in `ls -1 "${CHANGE_SCRIPTS}" | sort`; do
            # check name to see if it is a script to be executed or a patch file to be applied
            if [[ $SCRIPT =~ \.patch$ ]] ; then
                # a patch
                if [[ -x "${CHANGE_SCRIPTS}/${SCRIPT}" ]]; then
                    echo "ERROR: patch ${SCRIPT} is marked executable"
                    exit 3
                fi
            else
                # must be a script
                if [[ ! -x "${CHANGE_SCRIPTS}/${SCRIPT}" ]]; then
                    echo "ERROR: change script ${SCRIPT} not marked executable"
                    exit 3
                fi
            fi
        done
    fi
    
    return
}

run_recipe()
{
    local RECIPE_DIR="$1"
    local WORK_DIR="$2"

    ### STEP 1 delete files & dirs
    # deletion is done first to allow recursive delete first and then to fill in new data later
    local DELETE_ROOT="${RECIPE_DIR}/iso_delete"
    if [[ -d "${DELETE_ROOT}" ]]; then
        local FILE
        find "${DELETE_ROOT}" -type f -printf '%P\0' 2>/dev/null | while read -d $'\0' FILE
        do
            # using -f means nonexistant files are ignored
            rm -rf "${WORK_DIR}/${FILE}"
        done
    fi

    ### STEP 2: add/overwrite files
    local ADD_ROOT="${RECIPE_DIR}/iso_add"
    if [[ -d "${ADD_ROOT}" ]]; then
        rsync -a "${ADD_ROOT}/" "${WORK_DIR}"
    fi
    
    ### STEP 3: patches and scripts
    local CHANGE_SCRIPTS="${RECIPE_DIR}/iso_patch_and_script"
    if [[ -d "${CHANGE_SCRIPTS}" ]]; then
        
        # $CHANGE_SCRIPTS must have an absolute filename to make it work after pushd below
        CHANGE_SCRIPTS=$(realpath "${CHANGE_SCRIPTS}")
        
        # execute the scripts/patches in alphabetical order
        # allow to mix patches and scripts for maximum flexibility
        local SCRIPT
        local RET=0
        for SCRIPT in `ls -1 "${CHANGE_SCRIPTS}" | sort`; do
            # check name to see if it is a script to be executed or a patch file to be applied
            if [[ $SCRIPT =~ \.patch$ ]] ; then
                # a patch

                # use the --forward option to never consider a patch being reversed, just error out in that case, do not ask the user
                patch -p 1 --batch --forward -i "${CHANGE_SCRIPTS}/${SCRIPT}" -d "${WORK_DIR}" || RET=$?
                
                if [[ "$RET" -ne 0 ]]; then
                    echo "Error running patch ${SCRIPT}, returncode $RET, aborting"
                    exit 4
                fi
            else
                # change scripts are executed from the work-dir, so they can work without knowing about the whole dir-structure
                pushd "${WORK_DIR}" >/dev/null
                "${CHANGE_SCRIPTS}/${SCRIPT}" || RET=$?
                popd >/dev/null
                
                if [[ "$RET" -ne 0 ]]; then
                    echo "Error running change script ${SCRIPT}, returncode $RET, aborting"
                    exit 4
                fi
            fi
        done
    fi

    ### STEP 4: create SRM
    if [[ -d "${RECIPE_DIR}/build_into_srm" ]]; then
        create_srm "${RECIPE_DIR}/build_into_srm" "${WORK_DIR}/sysresccd/customize.srm"
        set_loadsrm_option "${WORK_DIR}/sysrescue.d/200-customize.yaml"
    fi
    
    return
}

#################################
# execution begins here

bin_check
parse_args "$@"

if [[ "$MODE" == "unpack" ]] ; then
    read_iso "$SOURCE" "$DEST"
elif [[ "$MODE" == "rebuild" ]] ; then
    write_iso_checks "$SOURCE" "$DEST"

    if [[ ! -z "$SRM_DIR" ]]; then
        create_srm "$SRM_DIR" "${SOURCE}/filesystem/sysresccd/customize.srm"
        set_loadsrm_option "${SOURCE}/filesystem/sysrescue.d/200-customize.yaml"
    fi
    
    write_iso "$SOURCE" "$DEST"
elif [[ "$MODE" == "auto" ]] ; then

    recipe_checks "$RECIPE_DIR"
    
    declare TMPDIR=""
    if [[ -z "$WORK_DIR" ]]; then
        TMPDIR=$(mktemp --tmpdir="." --directory tmp.XXXXXXXXXX)
        WORK_DIR=$TMPDIR
        # errors during main execution will leave the TMPDIR behind
        # useful for finding out what went wrong, but have to be cleaned manually
    fi
    
    read_iso "$SOURCE" "$WORK_DIR"
    run_recipe "$RECIPE_DIR" "$WORK_DIR/filesystem"
    write_iso_checks "$WORK_DIR" "$DEST"
    write_iso "$WORK_DIR" "$DEST"
    
    if [[ ! -z "$TMPDIR" ]]; then
        rm -rf "$TMPDIR"
    fi
fi

exit 0