make-bootable-alpine.sh

#!/bin/bash

ARCH="x86_64"
TARGET="/tmp/alpinefs"
ROOTGZ="/tmp/alpine-rootfs.tar.gz"
MIRROR="http://dl-cdn.alpinelinux.org/alpine"

echoerr() {
  printf "%s\n" "$*" >&2;
}

if [[ "$#" == "0" ]]; then
  echoerr "Usage: $0 RELEASE [DEVICE]"
  echoerr "Omitting DEVICE will set alpine rootfs up, but WILL NOT burn the image"
  exit 1
fi

RELEASE=$1
USBDEV=$2
MAJOR_RELEASE=$(echo $RELEASE | awk -F"." '{ print "v"$1"."$2 }')

RELURL="${MIRROR}/${MAJOR_RELEASE}/releases/${ARCH}/alpine-minirootfs-${RELEASE}-${ARCH}.tar.gz"
RELSHA=$(wget --quiet "http://dl-cdn.alpinelinux.org/alpine/${MAJOR_RELEASE}/releases/${ARCH}/alpine-minirootfs-${RELEASE}-${ARCH}.tar.gz.sha256" -O - | awk ' { print $1 } ')
ISOURL="${MIRROR}/${MAJOR_RELEASE}/releases/${ARCH}/alpine-standard-${RELEASE}-${ARCH}.iso"
ISOSHA=$(wget --quiet "http://dl-cdn.alpinelinux.org/alpine/${MAJOR_RELEASE}/releases/${ARCH}/alpine-standard-${RELEASE}-${ARCH}.iso.sha256" -O - | awk '{ print $1 }')

# Check if unpacking is already finished
if [[ ! -f "${TARGET}/unpack-ok" ]]; then
  echo "Downloading alpine rootfs"
  wget -q --show-progress -c "${RELURL}" -O "${ROOTGZ}"

  if [[ "$?" != "0" ]]; then
    echoerr "Download failed; aborting"
    exit 1
  fi
  DLRELSHA=$(sha256sum "${ROOTGZ}" | awk '{ print $1 }')
  shopt -s nocasematch
  if [[ "${RELSHA}" != "${DLRELSHA}" ]]; then
    echoerr "SHA256 checksum of rootfs failed; aborting"
    exit 1
  else
    echo "rootfs SHA256 checked out"
  fi
  shopt -u nocasematch


  echo "Unpacking alpine rootfs to ${TARGET}"
  if [[ ! -d "${TARGET}"  && -f "${TARGET}" ]]; then
    echoerr "Target \"${TARGET}\" is not a directory"
    exit 1
  else
    mkdir ${TARGET}
  fi

  tar xfz "${ROOTGZ}" -C "${TARGET}"
  #if [[ "$?" != "0" ]]; then
  #  echoerr "Unpacking rootfs failed; aborting"
  #  exit 1
  #fi

  touch "${TARGET}/unpack-ok"
else
  echo "Rootfs already unpacked; continuing..."
fi

if [[ ! -f "${TARGET}/config-ok" ]]; then
  echo "Adjusting inittab"
  sed '/tty[0-9]:/ s/^/#/' -i "${TARGET}/etc/inittab"
  printf 'console::respawn:/sbin/getty 38400 console\n' >> "${TARGET}/etc/inittab"

  echo "Adding mirror"
  printf '%s/%s/main\n' "${MIRROR}" "${MAJOR_RELEASE}" >| "${TARGET}/etc/apk/repositories"

  touch "${TARGET}/config-ok"
fi

echo "Initial configuration finished"

echo "Updating rootfs to the latest version"
systemd-nspawn -D "${TARGET}" /sbin/apk update
systemd-nspawn -D "${TARGET}" /sbin/apk upgrade

echo "Downloading alpine ${ARCH} ISO"
wget -q --show-progress -c "${ISOURL}" -O "${TARGET}/alpine-${ARCH}.iso"
DLISOSHA=$(sha256sum "${TARGET}/alpine-${ARCH}.iso" | awk '{ print $1 }')

shopt -s nocasematch
if [[ "${ISOSHA}" != "${DLISOSHA}" ]]; then
  echoerr "SHA256 checksum of rootfs failed; aborting"
  exit 1
else
  echo "ISO SHA256 checked out"
fi
shopt -u nocasematch

if [[ ! -d "${TARGET}/iso" ]]; then
  mkdir "${TARGET}/iso"
fi

echo "Adding required packages"
systemd-nspawn -D "${TARGET}" /sbin/apk add alpine-conf parted syslinux dosfstools e2fsprogs p7zip

echo "Extracting ISO"
if [[ ! -f "${TARGET}/iso-extract-ok" ]]; then
  # Do not extract any MBR info, there will be recreated by setup-bootable anyway
  systemd-nspawn -D "${TARGET}" /usr/bin/7z x -x!'[BOOT]/*' -o'/iso' "/alpine-${ARCH}.iso"

  if [[ "$?" != "0" ]]; then
    echoerr "Failed to unzip iso; aborting"
    exit 1
  else
    touch "${TARGET}/iso-extract-ok"
  fi
else
  echo "ISO is already extracted"
fi

echo "Enabling console output to /dev/ttyS0 for syslinux.cfg"
# Get the APPEND line that has the options
APPENDLINE=$(tail -n1 "${TARGET}/iso/boot/syslinux/syslinux.cfg")

# Split them up into an arry
OPTS=($APPENDLINE)
NEWAPPEND=""

# Reassemble them but drop any existing "console=" parts
for o in "${OPTS[@]}"; do
  if [[ ${o} =~ "console=" ]]; then
    echo "Ignoring existing console line"
  else
    NEWAPPEND=$(printf "%s %s" "${NEWAPPEND}" "${o}")
  fi
done

# Add the "console=" bit
NEWAPPEND=$(printf "%s console=ttyS0,115200" "${NEWAPPEND}")

# Replace last line in syslinux.cfg with the new one
head -n -1 "${TARGET}/iso/boot/syslinux/syslinux.cfg" >| "${TARGET}/iso/boot/syslinux/syslinux.new.cfg"
mv "${TARGET}/iso/boot/syslinux/syslinux.new.cfg" "${TARGET}/iso/boot/syslinux/syslinux.cfg"
echo "${NEWAPPEND}" | sed -e 's/^[[:space:]]*//' >> "${TARGET}/iso/boot/syslinux/syslinux.cfg"

if [[ "${USBDEV}" != "" ]]; then
  if [[ ! -b "${USBDEV}" ]]; then
    echoerr "${USBDEV} does not appear to be a block device; aborting"
    exit 1
  fi
  echo "Preparing partitions on ${USBDEV}"

  systemd-nspawn --bind ${USBDEV} -D "${TARGET}" /usr/sbin/parted ${USBDEV} --script \
    mklabel msdos \
    mkpart primary fat32 1MiB 100% \
    set 1 boot on
  if [[ "$?" != "0" ]]; then
    echoerr "Preparting partitions on ${USBDEV} failed; aborting"
  fi

  echo "Formatting ${USBDEV}1"
  systemd-nspawn --bind ""${USBDEV}"" --bind "${USBDEV}1" -D "${TARGET}" /sbin/mkdosfs -F32 "${USBDEV}1"
  if [[ "$?" != "0" ]]; then
    echoerr "mkdosfs -F32 ${USBDEV}1 failed; aborting"
    exit 1
  fi

  echo "Running /sbin/setup-bootable /iso ${USBDEV}1"
  systemd-nspawn --bind ${USBDEV} --bind "${USBDEV}1" -D "${TARGET}" /sbin/setup-bootable /iso "${USBDEV}1"
  if [[ "$?" != "0" ]]; then
    echoerr "setup-bootable failed; inspect ${USBDEV} manually"
    exit 1
  fi
else
  echoerr "No device provided; nothing more to do"
fi

echo "Script finished!"