# Install applications needed to build the live environment.
sudo apt-get install \
    debootstrap \
    squashfs-tools \
    xorriso \
    isolinux \
    syslinux-efi \
    grub-pc-bin \
    grub-efi-amd64-bin \
    grub-efi-ia32-bin \
    mtools \
    dosfstools
    
 # Create a directory where we will store all of the files we create throughout this guide. 
 mkdir -p "${HOME}/LIVE_BOOT"
 
 # Set up the base Debian environment.
 # Consult the list of debian mirrors. 
 # https://www.debian.org/mirror/list
 # Please change the URL in this command if there is a mirror that is closer to you.
 # We will use stable for this distribution and amd64 for the architecture.
 sudo debootstrap \
    --arch=amd64 \
    --variant=buildd \
    stable \
    "${HOME}/LIVE_BOOT/chroot" \
    https://deb.debian.org/debian

# Set a custom hostname for your Debian environment.
echo "custom-debian" | sudo tee "${HOME}/LIVE_BOOT/chroot/etc/hostname"

# Install a Linux kernel of your choosing. 
# The image linux-image-amd64 is chosen here. 
# live-boot is a necessity. 
# systemd-sys (or an equivalent) is also necessary to provide init. 

sudo chroot "${HOME}/LIVE_BOOT/chroot" << EOF
apt-get update && \
apt-get install -y --no-install-recommends \
    linux-image-amd64 \
    live-boot \
    systemd-sysv
EOF

# Install programs of your choosing, and then run apt-get clean to save some space. 
# I use --no-install-recommends to avoid superfluous packages. 
# You should decide what you need for your environment. 
# Have to try using 
# kde-plasma-desktop openbox-kde-session 
# xfce4 xfce4-session xfce4-goodies 
# obconf lxappearance-obconf lxinput lxrandr lxde

sudo chroot "${HOME}/LIVE_BOOT/chroot" << EOF
apt-get install -y --no-install-recommends \
    iwd \
    curl openssh-client \
    openbox xserver-xorg-core xserver-xorg xinit xterm \
    wget iputils-ping obconf network-manager \
    nano
EOF

#  Set the root password. 
# root will be the only user in this live environment by default, 
# but you may add additional users as needed. 

sudo chroot "${HOME}/LIVE_BOOT/chroot" passwd root

# Create directories that will contain files for our live environment files and scratch files. 

mkdir -p "${HOME}/LIVE_BOOT"/{staging/{EFI/BOOT,boot/grub/x86_64-efi,isolinux,live},tmp}

# Compress the chroot environment into a Squash filesystem.
sudo mksquashfs \
    "${HOME}/LIVE_BOOT/chroot" \
    "${HOME}/LIVE_BOOT/staging/live/filesystem.squashfs" \
    -e boot

# Copy the kernel and initramfs from inside the chroot to the live directory. 
cp "${HOME}/LIVE_BOOT/chroot/boot"/vmlinuz-* \
    "${HOME}/LIVE_BOOT/staging/live/vmlinuz" && \
cp "${HOME}/LIVE_BOOT/chroot/boot"/initrd.img-* \
    "${HOME}/LIVE_BOOT/staging/live/initrd"

# Create an ISOLINUX (Syslinux) boot menu. This boot menu is used when booting in BIOS/legacy mode. 
cat <<'EOF' > "${HOME}/LIVE_BOOT/staging/isolinux/isolinux.cfg"
UI vesamenu.c32

MENU TITLE Boot Menu
DEFAULT linux
TIMEOUT 600
MENU RESOLUTION 640 480
MENU COLOR border       30;44   #40ffffff #a0000000 std
MENU COLOR title        1;36;44 #9033ccff #a0000000 std
MENU COLOR sel          7;37;40 #e0ffffff #20ffffff all
MENU COLOR unsel        37;44   #50ffffff #a0000000 std
MENU COLOR help         37;40   #c0ffffff #a0000000 std
MENU COLOR timeout_msg  37;40   #80ffffff #00000000 std
MENU COLOR timeout      1;37;40 #c0ffffff #00000000 std
MENU COLOR msg07        37;40   #90ffffff #a0000000 std
MENU COLOR tabmsg       31;40   #30ffffff #00000000 std

LABEL linux
  MENU LABEL Custom Debian [BIOS/ISOLINUX]
  MENU DEFAULT
  KERNEL /live/vmlinuz
  APPEND initrd=/live/initrd boot=live

LABEL linux
  MENU LABEL Custom Debian [BIOS/ISOLINUX] (nomodeset)
  MENU DEFAULT
  KERNEL /live/vmlinuz
  APPEND initrd=/live/initrd boot=live nomodeset
EOF

# Create a second, similar, boot menu for GRUB. 
# This boot menu is used when booting in EFI/UEFI mode. 

cat <<'EOF' > "${HOME}/LIVE_BOOT/staging/boot/grub/grub.cfg"
insmod part_gpt
insmod part_msdos
insmod fat
insmod iso9660

insmod all_video
insmod font

set default="0"
set timeout=30

# If X has issues finding screens, experiment with/without nomodeset.

menuentry "Custom Debian [EFI/GRUB]" {
    search --no-floppy --set=root --label DEBLIVE
    linux ($root)/live/vmlinuz boot=live
    initrd ($root)/live/initrd
}

menuentry "Custom Debian [EFI/GRUB] (nomodeset)" {
    search --no-floppy --set=root --label DEBLIVE
    linux ($root)/live/vmlinuz boot=live nomodeset
    initrd ($root)/live/initrd
}
EOF

# Copy the grub.cfg file to the EFI BOOT directory. 

cp "${HOME}/LIVE_BOOT/staging/boot/grub/grub.cfg" "${HOME}/LIVE_BOOT/staging/EFI/BOOT/"

# Create a third boot config. 
# This config will be an early configuration file that is embedded 
# inside GRUB in the EFI partition. 
# This finds the root and loads the GRUB config from there. 

cat <<'EOF' > "${HOME}/LIVE_BOOT/tmp/grub-embed.cfg"
if ! [ -d "$cmdpath" ]; then
    # On some firmware, GRUB has a wrong cmdpath when booted from an optical disc.
    # https://gitlab.archlinux.org/archlinux/archiso/-/issues/183
    if regexp --set=1:isodevice '^(\([^)]+\))\/?[Ee][Ff][Ii]\/[Bb][Oo][Oo][Tt]\/?$' "$cmdpath"; then
        cmdpath="${isodevice}/EFI/BOOT"
    fi
fi
configfile "${cmdpath}/grub.cfg"
EOF

# Your LIVE_BOOT directory should now roughly look like this. 

# LIVE_BOOT/chroot/*tons of chroot files*
# LIVE_BOOT/staging/live/initrd
# LIVE_BOOT/staging/live/vmlinuz
# LIVE_BOOT/staging/live/filesystem.squashfs
# LIVE_BOOT/staging/isolinux/isolinux.cfg
# LIVE_BOOT/staging/EFI/BOOT
# LIVE_BOOT/staging/boot/grub/grub.cfg
# LIVE_BOOT/staging/boot/grub/x86_64-efi

# Copy BIOS/legacy boot required files into our workspace.

cp /usr/lib/ISOLINUX/isolinux.bin "${HOME}/LIVE_BOOT/staging/isolinux/" && \
cp /usr/lib/syslinux/modules/bios/* "${HOME}/LIVE_BOOT/staging/isolinux/"

# Copy EFI/modern boot required files into our workspace.

cp -r /usr/lib/grub/x86_64-efi/* "${HOME}/LIVE_BOOT/staging/boot/grub/x86_64-efi/"

# Generate an EFI bootable GRUB image.

grub-mkstandalone -O i386-efi \
    --modules="part_gpt part_msdos fat iso9660" \
    --locales="" \
    --themes="" \
    --fonts="" \
    --output="${HOME}/LIVE_BOOT/staging/EFI/BOOT/BOOTIA32.EFI" \
    "boot/grub/grub.cfg=${HOME}/LIVE_BOOT/tmp/grub-embed.cfg"

grub-mkstandalone -O x86_64-efi \
    --modules="part_gpt part_msdos fat iso9660" \
    --locales="" \
    --themes="" \
    --fonts="" \
    --output="${HOME}/LIVE_BOOT/staging/EFI/BOOT/BOOTx64.EFI" \
    "boot/grub/grub.cfg=${HOME}/LIVE_BOOT/tmp/grub-embed.cfg"

# Create a FAT16 UEFI boot disk image containing the EFI bootloaders. 

(cd "${HOME}/LIVE_BOOT/staging" && \
    dd if=/dev/zero of=efiboot.img bs=1M count=20 && \
    mkfs.vfat efiboot.img && \
    mmd -i efiboot.img ::/EFI ::/EFI/BOOT && \
    mcopy -vi efiboot.img \
        "${HOME}/LIVE_BOOT/staging/EFI/BOOT/BOOTIA32.EFI" \
        "${HOME}/LIVE_BOOT/staging/EFI/BOOT/BOOTx64.EFI" \
        "${HOME}/LIVE_BOOT/staging/boot/grub/grub.cfg" \
        ::/EFI/BOOT/
)

# Generate the .iso disc image file.

xorriso \
    -as mkisofs \
    -iso-level 3 \
    -o "${HOME}/LIVE_BOOT/debian-custom.iso" \
    -full-iso9660-filenames \
    -volid "DEBCUSTOM" \
    --mbr-force-bootable -partition_offset 16 \
    -joliet -joliet-long -rational-rock \
    -isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin \
    -eltorito-boot \
        isolinux/isolinux.bin \
        -no-emul-boot \
        -boot-load-size 4 \
        -boot-info-table \
        --eltorito-catalog isolinux/isolinux.cat \
    -eltorito-alt-boot \
        -e --interval:appended_partition_2:all:: \
        -no-emul-boot \
        -isohybrid-gpt-basdat \
    -append_partition 2 C12A7328-F81F-11D2-BA4B-00A0C93EC93B ${HOME}/LIVE_BOOT/staging/efiboot.img \
    "${HOME}/LIVE_BOOT/staging"