Create EspressoBIN ubuntu image

#!/bin/bash
# File: mkEspressoBIN-image

# Create SD-card ubuntu 16.04.3 image for booting EspressoBIN.
# Example usage:
# mkEspressoBIN-image [tarball [image [hostname [shortname [homes]]]]]
#
# Defaults:
# tarball  : rootfs.tar.bz2
# image    : EspressoBIN.img
# hostname : ebin.<currentdomain>
# shorthame: `whoami` or $shortname if exported
# homes    : <same your current account>
#
# Note: The tarball contains both the /boot directory and the rootfs; you can write it all to a single partition.
# For simplicity, just run this script from the same folder as the tarball, then it'll create the image.

[ "$EUID" -eq 0 ] && { echo "Please do not run this script as root"; exit 1; }

domain=`hostname -f`; domain=${domain#*.}

export tarball="${1:-rootfs.tar.bz2}"
export image="${2:-EspressoBIN.img}"
export hostname="${3-ebin.$domain}"
export shortname="${4:-${shortname:-`whoami`}}"
export homes="${5:-${HOME%/$USER}}"

export homedir="${shortname:+${homes:-home}/$shortname}"

[ "$homedir" ] && {
  export mkuser="adduser --home $homedir --shell /bin/bash $shortname; adduser $shortname sudo"
}

export networkconf=`cat <<EOF
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet manual

auto wan
iface wan inet dhcp
pre-up /sbin/ifconfig eth0 up
EOF`

export firstrun=`cat <<EOF
#!/bin/bash
apt-get update
apt-get upgrade
apt-get install nano openssh-server

$mkuser
sudo hostname -b $hostname
EOF`

echo -en "\033[1;32m"
cat << EOF
  tarball  : $tarball
  image    : $image
  hostname : $hostname
  shortname: $shortname
  homes    : $homes
  homedir  : $homedir
  domain   : $domain

  firstrun :
$firstrun

  networkconf:
$networkconf

EOF
echo -e "\033[m"

[ -f "$shortname.pub" ] && { [ -f "authorized_keys" ] || cat "$shortname.pub" >> "authorized_keys"; }

# A 512MB image woiuld probably need 451072 blocks, perhaps less
# quickly create an 1GB empty disk image using no space until it's written to:
dd if=/dev/zero of="$image" bs=1024 count=0 seek=975360

# The following is executed as privileged user (root):
sudo -E bash -c '
createImage(){
  # create one primary Linux partition:
  (echo n; echo p; echo 1; echo ""; echo ""; echo w) | fdisk "$image"

  # attach the image as a loop-back device:
  dev="$(losetup --show -f -P "$image")"

  # get a list of partitions (eg. /dev/loop0p1 /dev/loop0p2):
  partitions=("$dev"?*)

  # format partition:
  mkfs.ext4 "${partitions[0]}"

  # create mounting directory and mount partition:
  mkdir /mnt/p0; mount "${partitions[0]}" /mnt/p0

  # extract the files into the partition:
  echo -e "\033[1;34mExtracting files, please wait...\033[m"
  tar -xjf "$tarball" -C /mnt/p0

  # create a simple network configuration, which will allow you to use SSH:
  echo "$networkconf" >>/mnt/p0/etc/network/interfaces.d/all

  # create a "firstrun" executable for convenient setup:
  echo "$firstrun" >>/mnt/p0/usr/bin/firstrun
  chmod a+x /mnt/p0/usr/bin/firstrun

  [ "$homedir" ] && [ -f "authorized_keys" ] && {
    mkdir -p "/mnt/p0/$homedir/.ssh" && cat "authorized_keys" >>"/mnt/p0/$homedir/.ssh/authorized_keys"
  }

  # sync, unmount and remove mount directory:
  sync; umount /mnt/p0; rmdir /mnt/p0

  # detach the loopback device:
  losetup -d "$dev"
}
createImage'