build-ytl-image

#!/bin/sh

set -e

# This script will download a Ubuntu installation ISO image
# and modify it so that it will boot by default to an autoinstall
# mode and download our install configuration.

# Configurable settings:

# location of the original Ubuntu installation ISO image
DOWNLOAD_URL=https://releases.ubuntu.com/jammy/ubuntu-22.04.5-live-server-amd64.iso

# location where the clients should download the installation configuration
# (exported for the benefit of mangle-image below)
# "_gateway" can be used for testing
export AUTOINSTALL_URL=https://digabi.github.io/ytl-linux/autoinstall-config-22/

# Label on the modified ISO image
ISO_LABEL="YTL Ubuntu Install CD"

# Filename of the resulting image
RESULT_IMAGE=ytl-install-22.iso

#########################################
# Step 0: Check some prerequisites
#########################################

for prog in wget bsdtar xorriso; do
    if ! which $prog >/dev/null 2>&1; then
        echo "Missing $prog, cannot continue" 1>&2
        exit 1
    fi
done

#########################################
# Step 1: Download the original ISO image
#########################################

IMAGE=ubuntu.iso
if [ ! -e $IMAGE ]; then
    wget -O $IMAGE $DOWNLOAD_URL
fi

#########################################
# Step 2: Extract the image to a work directory
#########################################

WORKDIR=$(mktemp -d)
bsdtar xf $IMAGE  -C "$WORKDIR"
chmod -R u+w "$WORKDIR"

#########################################
# Step 3: Call an external script to modify the work directory
#########################################

./mangle-image "$WORKDIR"

#########################################
# Step 4: Repack the image
#########################################

# based on
#  https://help.ubuntu.com/community/InstallCDCustomization#Building_the_ISO_image

MBR_FILE=$(mktemp).mbr
EFI_FILE=$(mktemp).efi
dd if="$IMAGE" bs=1 count=446 of="$MBR_FILE"

# Extract EFI partition image
skip=$(/sbin/fdisk -l "$IMAGE" | fgrep '.iso2 ' | awk '{print $2}')
size=$(/sbin/fdisk -l "$IMAGE" | fgrep '.iso2 ' | awk '{print $4}')
dd if="$IMAGE" bs=512 skip="$skip" count="$size" of="$EFI_FILE"


xorriso -as mkisofs -r -V "$ISO_LABEL" \
            -iso-level 3 \
            -partition_offset 16 \
            --grub2-mbr "$MBR_FILE" \
            --mbr-force-bootable \
            -append_partition 2 0xEF "$EFI_FILE" \
            -appended_part_as_gpt \
            -c /boot.catalog \
            -b /boot/grub/i386-pc/eltorito.img \
            -no-emul-boot -boot-load-size 4 -boot-info-table --grub2-boot-info \
            -eltorito-alt-boot \
            -e '--interval:appended_partition_2:all::' \
            -no-emul-boot \
            -o "$RESULT_IMAGE" \
            "$WORKDIR"

#########################################
# Step 5: Clean up
#########################################

rm -rf "$WORKDIR" "$MBR_FILE" "$EFI_FILE"