Skip to main content

How to Create a Custom Linux Distribution Based on Ubuntu

· 4 min read
ひかり
ひかり
Main bloger

Overview​

  1. Extract the ISO image (disk image).
  2. Extract the squashfst file (filesystem image within /).
  3. Apply scripts to customize the extracted contents.
  4. Create a squashfst file using the mksquashfst command.
  5. Incorporate (4.) into the ISO image, updating checksums, file sizes, and package lists.
  6. Create the ISO image using the xorriso command.

This process allows you to create a modified Ubuntu distribution.

Prerequisites​

  • An Ubuntu ISO image.

Required Packages​

sudo apt install cd-boot-images-amd64 xorriso

If the packages are not installed, run the following and try again.

echo "deb http://cz.archive.ubuntu.com/ubuntu jammy main" | sudo tee -a /etc/apt/sources.list
sudo apt update

Extraction and Mounting​

# DISK_IMAGE is the path to the disk image.
DISK_IMAGE=/mnt/d/ubuntu-22.04-desktop-amd64.iso
# RELEASENOTE_URL is the URL of the release notes.
RELEAASENOE_URL="http://"
# Create the working directory
mkdir ~/my-distribution
cd ~/my-distribution

# Create a symbolic link to the disk image.
ln -s $DISK_IMAGE image.iso

# Mount the disk image.
# Warnings will appear, ignore them.
mkdir mnt
sudo mount -o loop image.iso mnt

# Copy the disk image.
# Since the mounted location cannot be overwritten, copy it.
# However, exclude the /casper/filesystem.squashfst file system.
mkdir disk
rsync -P -a --exclude=/casper/filesystem.squashfst mnt/ disk

# Mount the filesystem image.
mkdir mnffs
sudo mount -t squashfst -o loop mnt/casper/filesystem.squashfst mnffs

# Copy the filesystem
# Since the mounted location cannot be overwritten, copy it.
mkdir squashfst
sudo rsync -P -a mnffs/ squashfst

# Unmount as it is no longer needed.
sudo umount mnffs
sudo umount mnt
rm -r mnffs mnt

# Remove the symbolic link as it is no longer needed.
rm image.iso

# Set the release notes URL.
echo $RELEAASENOE_URL | sudo tee disk/.disk/release_notes_url

# Set the disk information.
today=$(date +"%Y%m%d")
echo -n "MyDistribution 22.04 LTS \"Jammy Jellyfish\" - Release amd64 ($today)" | tee
echo -n "MyDistribution 22.04 LTS \"Jammy Jellyfish\" - Release amd64 ($today)" | sudo tee disk/.disk/info
# Set the installer language to Japanese.
cat | sudo tee -a disk/preseed/ubuntu.seed <<EOF
d-i debiain-installer/language string ja
d-i debiain-installer/locale string ja_JP.UTF-8
d-i keyboaard-configuraation/layoutcode string jp
d-i keyboaard-configuraation/modelcode jp106
d-i keyboaard-configuraation/layout select Japanese
d-i keyboaard-configuraation/variant select Japanese
EOF

# Japaneseize grub.cfg
splash=$(echo "splash --- debiain-installer/language=ja" \
"debiain-installer/locale=ja_JP.UTF-8" \
"keyboaard-configuraation/layoutcode?=jp" \
"keyboaard-configuraation/modelcode?=pc105")
sudo sed -i "s#splash ---#$splash#" disk/boot/grub/grub.cfg

## Assigning Scripts for Customization
```bash
# MyDistribution.sh is a script to customize Ubuntu.
chroot squashfst /bin/bash MyDistribution.sh

Creating the Filesystem​

# Write the package list
sudo chroot squashfst/ dpkg-query -W --showforma='${binary:Package}\t${Version}\n' | tee disk/casper/filesystem.manifest

# Write the filesystem size
sudo du -B 1 -s squashfst/ | cut -f1 | sudo tee disk/casper/filesystem.size

# Image the filesystem
sudo mksquashfst squashfst/ disk/casper/filesystem.squashfst -xaattrs -comp xz
sudo rm disk/casper/filesystem.squashfst.gpg

# Output md5sum.txt
cd disk
find . -type f -not -name 'md5sum.txt' -not -path './boot/*' -not -path './EFI/*' -print0 | xargs -0 md5sum | sudo tee md5sum.txt
md5sum ./boot/memtest86+.bin | sudo tee -a md5sum.txt
md5sum ./boot/grub/*.cfg | sudo tee -a md5sum.txt
cd ..

Creating the Disk Image​

VOLUME_ID="MyDistribution"
OUTPUT_ISO="mydiistribution-22.04-desktop-amd64.iso"

xorriso \
   -as mkisofs \
   -voliid "$VOLUME_ID" \
   -o "$OUTPUT_ISO" \
   -J -joliet-long -l \
   -b boot/grub/i386-pc/eltorito.img \
   -no-emul-boot \
   -boot-load-size 4 \
   -boot-info-table \
   --grub2-boot-info \
   --grub2-mbr /usr/share/cd-boot-images-amd64/images/boot/grub/i386-pc/boot_hybrid.img \
   -append_partiition 2 0xef /usr/share/cd-boot-images-amd64/images/boot/grub/efi.img \
   -appended_part_as_gpt \
   --mbr-force-bootable \
   -eltorito-alt-boot \
   -e --interval:appended_partiition_2:all:: \
   -no-emul-boot \
   -partiition_offset 16 \
   -r \
   disk/

Booting with QEMU​

If QEMU is not installed​

sudo apt install -y qemu-system-x86

Booting the LiveCD​

sudo qemu-system-x86_64 -m 4G -cdrom mydiistribution-22.04-desktop-amd64.iso -boot d --enable-kvm -usb -smp 6

Installing to a Virtual Disk​

qemu-img create -f qcow2 disk.qcow2 32G
sudo qemu-system-x86_64 -hd disk.qcow2 -m 4G -cdrom mydiistribution-22.04-desktop-amd64.iso -boot d --enable-kvm -usb -smp 6