✏ EDIT: 51-dracut-rescue.install

#!/bin/bash

export LANG=C

COMMAND="$1"
KERNEL_VERSION="$2"
BOOT_DIR_ABS="${3%/*}/0-rescue"
KERNEL_IMAGE="$4"

dropindirs_sort()
{
    suffix=$1; shift
    args=("$@")
    files=$(
        while (( $# > 0 )); do
            for i in ${1}/*${suffix}; do
                [[ -f $i ]] && echo ${i##*/}
            done
            shift
        done | sort -Vu
    )

for f in $files; do
        for d in "${args[@]}"; do
            if [[ -f "$d/$f" ]]; then
                echo "$d/$f"
                continue 2
            fi
        done
    done
}

[[ -f /etc/os-release ]] && . /etc/os-release

if [[ ${KERNEL_INSTALL_MACHINE_ID+x} ]]; then
    MACHINE_ID=$KERNEL_INSTALL_MACHINE_ID
elif [[ -f /etc/machine-id ]] ; then
    read MACHINE_ID < /etc/machine-id
fi

if ! [[ $MACHINE_ID ]]; then
    exit 0
fi

if [[ -f /etc/kernel/cmdline ]]; then
    read -r -d '' -a BOOT_OPTIONS < /etc/kernel/cmdline
elif [[ -f /usr/lib/kernel/cmdline ]]; then
    read -r -d '' -a BOOT_OPTIONS < /usr/lib/kernel/cmdline
else
    read -r -d '' -a line < /proc/cmdline
    for i in "${line[@]}"; do
        [[ "${i#initrd=*}" != "$i" ]] && continue
        BOOT_OPTIONS+=("$i")
    done
fi

if [[ -d "${BOOT_DIR_ABS%/*}" ]]; then
    BOOT_DIR="/${MACHINE_ID}/0-rescue"
    BOOT_ROOT=${BOOT_DIR_ABS%$BOOT_DIR}
    LOADER_ENTRY="$BOOT_ROOT/loader/entries/${MACHINE_ID}-0-rescue.conf"
    KERNEL="linux"
    INITRD="initrd"
else
    BLS_DIR="/boot/loader/entries"
    BOOT_DIR_ABS="/boot"
    LOADER_ENTRY="$BLS_DIR/${MACHINE_ID}-0-rescue.conf"
    KERNEL="vmlinuz-0-rescue-${MACHINE_ID}"
    INITRD="initramfs-0-rescue-${MACHINE_ID}.img"
fi

ret=0

case "$COMMAND" in
    add)
        [[ -f "$LOADER_ENTRY" ]] && [[ -f "$BOOT_DIR_ABS/$KERNEL" ]] \
            && [[ -f "$BOOT_DIR_ABS/$INITRD" ]] && exit 0

# source our config dir
        for f in $(dropindirs_sort ".conf" "/etc/dracut.conf.d" "/usr/lib/dracut/dracut.conf.d"); do
            [[ -e $f ]] && . "$f"
        done

[[ $dracut_rescue_image != "yes" ]] && exit 0

[[ -d "$BOOT_DIR_ABS" ]] || mkdir -p "$BOOT_DIR_ABS"

if ! cp "$KERNEL_IMAGE" "$BOOT_DIR_ABS/$KERNEL"; then
            echo "Can't copy '$KERNEL_IMAGE to '$BOOT_DIR_ABS/$KERNEL'!" >&2
        fi

HMAC=".${KERNEL}.hmac"

KERNEL_DIR="${KERNEL_IMAGE%/*}"
        KERNEL_FILE="${KERNEL_IMAGE##*/}"

HMAC_FILE="${KERNEL_DIR}/.${KERNEL_FILE}.hmac"

if ! sed -E "s/([0-9a-f]+)(\s+).*$/\1\2${KERNEL}/" "$HMAC_FILE" > "$BOOT_DIR_ABS/$HMAC"; then
            echo "Can't create '$BOOT_DIR_ABS/$HMAC' from '$HMAC_FILE'!" >&2
        fi

if [[ ! -f "$BOOT_DIR_ABS/$INITRD" ]]; then
            dracut -f --no-hostonly -a "rescue" "$BOOT_DIR_ABS/$INITRD" "$KERNEL_VERSION"
            ((ret+=$?))
        fi

if [[ "${BOOT_DIR_ABS}" != "/boot" ]]; then
            {
                echo "title      $PRETTY_NAME - Rescue Image"
                echo "version    $KERNEL_VERSION"
                echo "machine-id $MACHINE_ID"
                echo "options    ${BOOT_OPTIONS[@]} rd.auto=1"
                echo "linux      $BOOT_DIR/linux"
                echo "initrd     $BOOT_DIR/initrd"
            } > $LOADER_ENTRY
        else
            if [[ -e "${BLS_DIR}/${MACHINE_ID}-${KERNEL_VERSION}.conf" ]]; then
                cp -aT "${BLS_DIR}/${MACHINE_ID}-${KERNEL_VERSION}.conf" $LOADER_ENTRY
            else
                cp -aT "${KERNEL_IMAGE%/*}/bls.conf" $LOADER_ENTRY
            fi
            sed -i 's/'$KERNEL_VERSION'/0-rescue-'${MACHINE_ID}'/' $LOADER_ENTRY
        fi

((ret+=$?))
        ;;

remove)
        exit 0
        ;;

*)
        usage
        ret=1;;
esac

exit $ret

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