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ubuntu-preseed-iso-generator.sh
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ubuntu-preseed-iso-generator.sh
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#!/bin/bash
set -Eeuo pipefail
function cleanup() {
trap - SIGINT SIGTERM ERR EXIT
if [ -n "${tmpdir+x}" ]; then
rm -rf "$tmpdir"
log "🚽 Deleted temporary working directory $tmpdir"
fi
}
trap cleanup SIGINT SIGTERM ERR EXIT
script_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" &>/dev/null && pwd -P)
[[ ! -x "$(command -v date)" ]] && echo "💥 date command not found." && exit 1
today=$(date +"%Y-%m-%d")
function log() {
echo >&2 -e "[$(date +"%Y-%m-%d %H:%M:%S")] ${1-}"
}
function die() {
local msg=$1
local code=${2-1} # Bash parameter expansion - default exit status 1. See https://wiki.bash-hackers.org/syntax/pe#use_a_default_value
log "$msg"
exit "$code"
}
usage() {
cat <<EOF
Usage: $(basename "${BASH_SOURCE[0]}") [-h] [-k] [-v] [-p preseed-configuration-file] [-s source-iso-file] [-d destination-iso-file]
💁 This script will create fully-automated Ubuntu 20.04 Focal Fossa installation media.
Available options:
-h, --help Print this help and exit
-v, --verbose Print script debug info
-p, --preseed Path to preseed configuration file.
-k, --no-verify Disable GPG verification of the source ISO file. By default SHA256SUMS-$today and
SHA256SUMS-$today.gpg in ${script_dir} will be used to verify the authenticity and integrity
of the source ISO file. If they are not present the latest daily SHA256SUMS will be
downloaded and saved in ${script_dir}. The Ubuntu signing key will be downloaded and
saved in a new keyring in ${script_dir}
-s, --source Source ISO file. By default the latest daily ISO for Ubuntu 20.04 will be downloaded
and saved as ${script_dir}/ubuntu-original-$today.iso
That file will be used by default if it already exists.
-d, --destination Destination ISO file. By default ${script_dir}/ubuntu-preseed-$today.iso will be
created, overwriting any existing file.
EOF
exit
}
function parse_params() {
# default values of variables set from params
preseed_file=""
source_iso="${script_dir}/ubuntu-original-$today.iso"
destination_iso="${script_dir}/ubuntu-preseed-$today.iso"
gpg_verify=1
while :; do
case "${1-}" in
-h | --help) usage ;;
-v | --verbose) set -x ;;
-k | --no-verify) gpg_verify=0 ;;
-p | --preseed)
preseed_file="${2-}"
shift
;;
-s | --source)
source_iso="${2-}"
shift
;;
-d | --destination)
destination_iso="${2-}"
shift
;;
-?*) die "Unknown option: $1" ;;
*) break ;;
esac
shift
done
log "👶 Starting up..."
# check required params and arguments
[[ -z "${preseed_file}" ]] && die "💥 preseed file was not specified."
[[ ! -f "$preseed_file" ]] && die "💥 preseed file could not be found."
if [ "${source_iso}" != "${script_dir}/ubuntu-original-$today.iso" ]; then
[[ ! -f "${source_iso}" ]] && die "💥 Source ISO file could not be found."
fi
destination_iso=$(realpath "${destination_iso}")
source_iso=$(realpath "${source_iso}")
return 0
}
ubuntu_gpg_key_id="843938DF228D22F7B3742BC0D94AA3F0EFE21092"
parse_params "$@"
tmpdir=$(mktemp -d)
if [[ ! "$tmpdir" || ! -d "$tmpdir" ]]; then
die "💥 Could not create temporary working directory."
else
log "📁 Created temporary working directory $tmpdir"
fi
log "🔎 Checking for required utilities..."
[[ ! -x "$(command -v 7z)" ]] && die "💥 7z is not installed."
[[ ! -x "$(command -v sed)" ]] && die "💥 sed is not installed."
[[ ! -x "$(command -v curl)" ]] && die "💥 curl is not installed."
[[ ! -x "$(command -v mkisofs)" ]] && die "💥 mkisofs is not installed."
[[ ! -x "$(command -v gpg)" ]] && die "💥 gpg is not installed."
log "👍 All required utilities are installed."
if [ ! -f "${source_iso}" ]; then
log "🌎 Downloading current daily ISO image for Ubuntu 20.04 Focal Fossa..."
curl -NsSL "https://cdimage.ubuntu.com/focal/daily-live/current/focal-desktop-amd64.iso" -o "${source_iso}"
log "👍 Downloaded and saved to ${source_iso}"
else
log "☑️ Using existing ${source_iso} file."
if [ ${gpg_verify} -eq 1 ]; then
if [ "${source_iso}" != "${script_dir}/ubuntu-original-$today.iso" ]; then
log "⚠️ Automatic GPG verification is enabled. If the source ISO file is not the latest daily image, verification will fail!"
fi
fi
fi
if [ ${gpg_verify} -eq 1 ]; then
if [ ! -f "${script_dir}/SHA256SUMS-${today}" ]; then
log "🌎 Downloading SHA256SUMS & SHA256SUMS.gpg files..."
curl -NsSL "https://cdimage.ubuntu.com/focal/daily-live/current/SHA256SUMS" -o "${script_dir}/SHA256SUMS-${today}"
curl -NsSL "https://cdimage.ubuntu.com/focal/daily-live/current/SHA256SUMS.gpg" -o "${script_dir}/SHA256SUMS-${today}.gpg"
else
log "☑️ Using existing SHA256SUMS-${today} & SHA256SUMS-${today}.gpg files."
fi
if [ ! -f "${script_dir}/${ubuntu_gpg_key_id}.keyring" ]; then
log "🌎 Downloading and saving Ubuntu signing key..."
gpg -q --no-default-keyring --keyring "${script_dir}/${ubuntu_gpg_key_id}.keyring" --keyserver "hkp://keyserver.ubuntu.com" --recv-keys "${ubuntu_gpg_key_id}"
log "👍 Downloaded and saved to ${script_dir}/${ubuntu_gpg_key_id}.keyring"
else
log "☑️ Using existing Ubuntu signing key saved in ${script_dir}/${ubuntu_gpg_key_id}.keyring"
fi
log "🔐 Verifying ${source_iso} integrity and authenticity..."
gpg -q --keyring "${script_dir}/${ubuntu_gpg_key_id}.keyring" --verify "${script_dir}/SHA256SUMS-${today}.gpg" "${script_dir}/SHA256SUMS-${today}" 2>/dev/null
if [ $? -ne 0 ]; then
rm -f "${script_dir}/${ubuntu_gpg_key_id}.keyring~"
die "👿 Verification of SHA256SUMS signature failed."
fi
rm -f "${script_dir}/${ubuntu_gpg_key_id}.keyring~"
digest=$(sha256sum "${source_iso}" | cut -f1 -d ' ')
set +e
grep -Fq "$digest" "${script_dir}/SHA256SUMS-${today}"
if [ $? -eq 0 ]; then
log "👍 Verification succeeded."
set -e
else
die "👿 Verification of ISO digest failed."
fi
else
log "🤞 Skipping verification of source ISO."
fi
log "🔧 Extracting ISO image..."
7z -y x "${source_iso}" -o"$tmpdir" >/dev/null
rm -rf "$tmpdir/"'[BOOT]'
log "👍 Extracted to $tmpdir"
log "🧩 Adding preseed parameters to kernel command line..."
# These are for UEFI mode
sed -i -e 's,file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash,file=/cdrom/preseed/custom.seed auto=true priority=critical boot=casper automatic-ubiquity quiet splash noprompt noshell,g' "$tmpdir/boot/grub/grub.cfg"
sed -i -e 's,file=/cdrom/preseed/ubuntu.seed maybe-ubiquity iso-scan/filename=${iso_path} quiet splash,file=/cdrom/preseed/custom.seed auto=true priority=critical boot=casper automatic-ubiquity quiet splash noprompt noshell,g' "$tmpdir/boot/grub/loopback.cfg"
# This one is used for BIOS mode
cat <<EOF > "$tmpdir/isolinux/txt.cfg"
default live-install
label live-install
menu label ^Install Ubuntu
kernel /casper/vmlinuz
append file=/cdrom/preseed/custom.seed auto=true priority=critical boot=casper automatic-ubiquity initrd=/casper/initrd quiet splash noprompt noshell ---
EOF
log "👍 Added parameters to UEFI and BIOS kernel command lines."
log "🧩 Adding preseed configuration file..."
cp "$preseed_file" "$tmpdir/preseed/custom.seed"
log "👍 Added preseed file"
log "👷 Updating $tmpdir/md5sum.txt with hashes of modified files..."
# Using the full list of hashes causes long delays at boot.
# For now, just include a couple of the files we changed.
md5=$(md5sum "$tmpdir/boot/grub/grub.cfg" | cut -f1 -d ' ')
echo "$md5 ./boot/grub/grub.cfg" > "$tmpdir/md5sum.txt"
md5=$(md5sum "$tmpdir/boot/grub/loopback.cfg" | cut -f1 -d ' ')
echo "$md5 ./boot/grub/loopback.cfg" >> "$tmpdir/md5sum.txt"
log "👍 Updated hashes."
log "📦 Repackaging extracted files into an ISO image..."
cd "$tmpdir"
mkisofs -quiet -D -r -V "ubuntu-preseed-$today" -cache-inodes -J -l -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -eltorito-alt-boot -e boot/grub/efi.img -no-emul-boot -o "${destination_iso}" .
cd "$OLDPWD"
log "👍 Repackaged into ${destination_iso}"
die "✅ Completed." 0