Unpack, edit and repack an initrd image for Volumio

init-edit.sh

#!/usr/bin/env bash
# Basic usage:  <init-editd -f filename>
# Example: ${SCRIPT} -f uIinitrd
# Notes: The script will determine how the initrd has been compressed and unpack/ repack accordingly
# Based on Gé's script (init-edit.sh)

SRC="$(dirname "$(realpath "${BASH_SOURCE[0]}")")"
SCRIPT=$(basename "${BASH_SOURCE[0]}")
compress=pigz
function exit_error() {
  echo "${SCRIPT} failed at $1"
  echo "Cleaning up ${TMPWORK}.."
  rm -r "${TMPWORK}"
  exit 1
}
trap 'exit_error ${LINENO}' INT ERR

TMPWORK="$(mktemp -d "${TMPDIR:-/var/tmp}/initramfs_XXXXXX")" || exit_error

# Help function
function HELP() {
  cat <<-EOF
Help documentation for ${SCRIPT}
Basic usage: ${SCRIPT} <INITRDFILE>
Arguments:
  -f <INITRDFILE>  Path to the initrd image to edit 
  -v               verbose
  -a <arch>        mkimage arch
  -c <compression> comprssion tool (default pigz)
Example: Edit /boot/uIinitrd :
         ${SCRIPT} -f /boot/uIinitrd
EOF
  exit 1
}

function input_prompt() {
  read -rp "Do you wish to continue [Y/N] ? " response
  echo
  case $response in
  [Yy]*)
    echo ""
    ;;
  [Nn]*)
    echo "Aborting init-editing"
    exit_error "init-editing"
    ;;
  *)
    echo "Assuming you mean No, please answer [Yy]es or [Nn]o the next time..."
    exit_error "init-editing"
    ;;
  esac
}

#if ! command -v nano &>/dev/null; then
#  echo "This script requires text editor 'nano'"
#  echo "Please install it with 'sudo apt install nano'"
#  exit 1
#fi

NUMARGS=$#
if [ "$NUMARGS" -eq 0 ]; then
  HELP
fi

while getopts a:f:h:v FLAG; do
  case $FLAG in
  a)
    arch="${OPTARG}"
    ;;
  c)
    compress="${OPTARG}"
    ;;
  f)
    INITRD_PATH="${OPTARG}"
    ;;
  h) #show help
    HELP
    ;;
  v)
    verbose=y
    ;;
  /?) #unrecognized option - show help
    echo -e \\n"Option -${BOLD}${OPTARG}${NORM} not allowed."
    HELP
    ;;
  esac
done

if [[ -z ${INITRD_PATH} ]]; then
  echo ""
  echo "${SCRIPT}: missing argument(s)"
  HELP
  exit 1
fi

if [[ ! -f ${INITRD_PATH} ]]; then
  echo ""
  echo "${SCRIPT}: ${INITRD_PATH} does not exist"
  HELP
  exit 1
fi

if compgen -G "${TMPWORK}/*"; then
  echo "Workarea exists, cleaning it..."
  rm -r "${TMPWORK:?}"/* >/dev/null 2>&1
fi
INITRD_NAME=$(basename "${INITRD_PATH}")
INITRD_DIR=$(dirname "$(realpath "${INITRD_PATH}")")
echo "Copying ${INITRD_NAME} from ${INITRD_DIR} to ${TMPWORK}..."
cp "${INITRD_PATH}" "${TMPWORK}/${INITRD_NAME}"
WRK_INITRD="${TMPWORK}/${INITRD_NAME}"
WORK_DIR=${TMPWORK}/root
mkdir "${WORK_DIR}"
pushd "${WORK_DIR}" || exit 1

FORMAT=$(file "${WRK_INITRD}" | grep -o "RAMDisk Image")
if [[ "$FORMAT" == "RAMDisk Image" ]]; then
  echo "Unpacking RAMDisk image ${WRK_INITRD}..."
  dd if="${WRK_INITRD}" bs=64 skip=1 | gzip -dc | cpio -div
  # Figure out arch
  # shellcheck source=/dev/null
  source ./conf/arch.conf

  echo "Open ${WORK_DIR}/init to edit.."
  input_prompt

  echo "Creating a new ${INITRD_NAME} image (${DPKG_ARCH}), please wait..."
  OPTS=("-o")
  [[ "${verbose}" = y ]] && OPTS+=("-v") || OPTS+=("--quiet")
  compress="${compress} -9"
  find . -print0 | cpio "${OPTS[@]}" -0 --format=newc | ${compress} >"${INITRD_NAME}.new"
  [[ -n "${arch}" ]] && [[ "${arch}" != "${DPKG_ARCH/hf/}" ]] && echo "Warning: Prescribed ${arch} != ${DPKG_ARCH/hf/}"
  mkimage -A "${DPKG_ARCH/hf/}" -O linux -T ramdisk -C gzip -n uInitrd -d "${INITRD_NAME}.new" "${INITRD_DIR}/${INITRD_NAME}.new"
else
  echo "Unpacking gzip compressed ${INITRD_NAME}..."
  zcat "${WRK_INITRD}" | cpio -idmv >/dev/null 2>&1
  input_prompt

  echo "Creating a new ${INITRD_NAME}, please wait..."
  find . -print0 | cpio --quiet -o -0 --format=newc | gzip -9 >"${INITRD_DIR}/${INITRD_NAME}.new"
fi

echo "Done. Moving ${INITRD_PATH} --> .old"
echo "Cleaning up..."
popd || exit 1
mv "${INITRD_PATH}" "${INITRD_PATH}.old"
mv "${INITRD_PATH}.new" "${INITRD_PATH}"
rm -r "${TMPWORK:?}"
ls -la --color "${INITRD_DIR}"