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How to create a custom Ubuntu live from scratch

This procedure shows how to create a bootable and installable Ubuntu Live (along with the automatic hardware detection and configuration) from scratch. The steps described below are also available in this repo in the /scripts directory.

Authors

  • Marcos Vallim - Founder, Author, Development, Test, Documentation - mvallim
  • Ken Gilmer - Commiter, Development, Test, Documentation - kgilmer

See also the list of contributors who participated in this project.

Ways of Using this Tutorial

  • (Recommended) follow the directions step by step below to understand how to build an Ubuntu ISO.
  • Run the build.sh script in the scripts directory after checking this repo out locally.
  • Fork this repo and run the github action build. This will generate an ISO in your github account.

build-bionic build-focal

Terms

  • build system - the computer environment running the build scripts that generate the ISO.
  • live system - the computer environment that runs from the live OS, generated by a build system. This may also be referred to as the chroot environment.
  • target system - the computer environment that runs after installation has completed from a live system.

Prerequisites (GNU/Linux Debian/Ubuntu)

Install packages we need in the build system required by our scripts.

sudo apt-get install \
    binutils \
    debootstrap \
    squashfs-tools \
    xorriso \
    grub-pc-bin \
    grub-efi-amd64-bin \
    mtools
mkdir $HOME/live-ubuntu-from-scratch

Bootstrap and Configure Ubuntu

debootstrap is a program for generating OS images. We install it into our build system to begin generating our ISO.

  • Checkout bootstrap

    sudo debootstrap \
   --arch=amd64 \
   --variant=minbase \
   focal \
   $HOME/live-ubuntu-from-scratch/chroot \
   http://us.archive.ubuntu.com/ubuntu/

    debootstrap is used to create a Debian base system from scratch, without requiring the availability of dpkg or apt. It does this by downloading .deb files from a mirror site, and carefully unpacking them into a directory which can eventually be chrooted into.

  • Configure external mount points

    sudo mount --bind /dev $HOME/live-ubuntu-from-scratch/chroot/dev

sudo mount --bind /run $HOME/live-ubuntu-from-scratch/chroot/run

    As we will be updating and installing packages (grub among them), these mount points are necessary inside the chroot environment, so we are able to finish the installation without errors.

Define chroot environment

A chroot on Unix operating systems is an operation that changes the apparent root directory for the current running process and its children. A program that is run in such a modified environment cannot name (and therefore normally cannot access) files outside the designated directory tree. The term "chroot" may refer to the chroot system call or the chroot wrapper program. The modified environment is called a chroot jail.

Reference: https://en.wikipedia.org/wiki/Chroot

From this point we will be configuring the live system.

  1. Access chroot environment

    sudo chroot $HOME/live-ubuntu-from-scratch/chroot

  2. Configure mount points, home and locale

    mount none -t proc /proc

mount none -t sysfs /sys

mount none -t devpts /dev/pts

export HOME=/root

export LC_ALL=C

    These mount points are necessary inside the chroot environment, so we are able to finish the installation without errors.

  3. Set a custom hostname

    echo "ubuntu-fs-live" > /etc/hostname

  4. Configure apt sources.list

    cat <<EOF > /etc/apt/sources.list
deb http://us.archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ focal main restricted universe multiverse

deb http://us.archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ focal-security main restricted universe multiverse

deb http://us.archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ focal-updates main restricted universe multiverse
EOF

  5. Update indexes packages

    apt-get update

  6. Install systemd

    apt-get install -y libterm-readline-gnu-perl systemd-sysv

    systemd is a system and service manager for Linux. It provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux control groups, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic.

  7. Configure machine-id and divert

    dbus-uuidgen > /etc/machine-id

ln -fs /etc/machine-id /var/lib/dbus/machine-id

    The /etc/machine-id file contains the unique machine ID of the local system that is set during installation or boot. The machine ID is a single newline-terminated, hexadecimal, 32-character, lowercase ID. When decoded from hexadecimal, this corresponds to a 16-byte/128-bit value. This ID may not be all zeros.

    dpkg-divert --local --rename --add /sbin/initctl

ln -s /bin/true /sbin/initctl

    dpkg-divert is the utility used to set up and update the list of diversions.

  8. Upgrade packages

    apt-get -y upgrade

  9. Install packages needed for Live System

    apt-get install -y \
    sudo \
    ubuntu-standard \
    casper \
    lupin-casper \
    discover \
    laptop-detect \
    os-prober \
    network-manager \
    resolvconf \
    net-tools \
    wireless-tools \
    wpagui \
    locales \
    grub-common \
    grub-gfxpayload-lists \
    grub-pc \
    grub-pc-bin \
    grub2-common
    apt-get install -y --no-install-recommends linux-generic

  10. Graphical installer

    apt-get install -y \
   ubiquity \
   ubiquity-casper \
   ubiquity-frontend-gtk \
   ubiquity-slideshow-ubuntu \
   ubiquity-ubuntu-artwork

    The next steps will appear, as a result of the packages that will be installed from the previous step, this will happen without anything having to be informed or executed.

    1. Configure keyboard

    1. Console setup

  11. Install window manager

    apt-get install -y \
    plymouth-theme-ubuntu-logo \
    ubuntu-gnome-desktop \
    ubuntu-gnome-wallpapers

  12. Install useful applications

    apt-get install -y \
    clamav-daemon \
    terminator \
    apt-transport-https \
    curl \
    vim \
    nano \
    less

  13. Install Visual Studio Code (optional)

  14. Download and install the key

    curl https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor > microsoft.gpg

install -o root -g root -m 644 microsoft.gpg /etc/apt/trusted.gpg.d/

echo "deb [arch=amd64] https://packages.microsoft.com/repos/vscode stable main" > /etc/apt/sources.list.d/vscode.list

rm microsoft.gpg

  15. Then update the package cache and install the package using

    apt-get update

apt-get install -y code

  16. Install Google Chrome (optional)

  17. Download and install the key

    wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -

echo "deb http://dl.google.com/linux/chrome/deb/ stable main" > /etc/apt/sources.list.d/google-chrome.list

  18. Then update the package cache and install the package using

    apt-get update

apt-get install google-chrome-stable

  19. Install Java JDK 8 (optional)

    apt-get install -y \
    openjdk-8-jdk \
    openjdk-8-jre

  20. Remove unused applications (optional)

    apt-get purge -y \
    transmission-gtk \
    transmission-common \
    gnome-mahjongg \
    gnome-mines \
    gnome-sudoku \
    aisleriot \
    hitori

  21. Remove unused packages

    apt-get autoremove -y

  22. Reconfigure packages

  23. Generate locales

    dpkg-reconfigure locales

    1. Select locales

    2. Select default locale

  24. Reconfigure resolvconf

    dpkg-reconfigure resolvconf

    1. Confirm changes

  25. Configure network-manager

    cat <<EOF > /etc/NetworkManager/NetworkManager.conf
[main]
rc-manager=resolvconf
plugins=ifupdown,keyfile
dns=dnsmasq

[ifupdown]
managed=false
EOF

  26. Reconfigure network-manager

    dpkg-reconfigure network-manager

  27. Cleanup the chroot environment

  28. If you installed software, be sure to run

    truncate -s 0 /etc/machine-id

  29. Remove the diversion

    rm /sbin/initctl

dpkg-divert --rename --remove /sbin/initctl

  30. Clean up

    apt-get clean

rm -rf /tmp/* ~/.bash_history

umount /proc

umount /sys

umount /dev/pts

export HISTSIZE=0

exit

Unbind mount points

sudo umount $HOME/live-ubuntu-from-scratch/chroot/dev

sudo umount $HOME/live-ubuntu-from-scratch/chroot/run

Create the CD image directory and populate it

We are now back in our build environment after setting up our live system and will continue creating files necessary to generate the ISO.

  1. Access build directory

    cd $HOME/live-ubuntu-from-scratch

  2. Create directories

    mkdir -p image/{casper,isolinux,install}

  3. Copy kernel images

    sudo cp chroot/boot/vmlinuz-**-**-generic image/casper/vmlinuz

sudo cp chroot/boot/initrd.img-**-**-generic image/casper/initrd

  4. Copy memtest86+ binary (BIOS)

    sudo cp chroot/boot/memtest86+.bin image/install/memtest86+

  5. Download and extract memtest86 binary (UEFI)

    wget --progress=dot https://www.memtest86.com/downloads/memtest86-usb.zip -O image/install/memtest86-usb.zip

unzip -p image/install/memtest86-usb.zip memtest86-usb.img > image/install/memtest86

rm -f image/install/memtest86-usb.zip

GRUB menu configuration

  1. Access build directory

    cd $HOME/live-ubuntu-from-scratch

  2. Create base point access file for grub

    touch image/ubuntu

  3. Create image/isolinux/grub.cfg

    cat <<EOF > image/isolinux/grub.cfg

search --set=root --file /ubuntu

insmod all_video

set default="0"
set timeout=30

menuentry "Try Ubuntu FS without installing" {
   linux /casper/vmlinuz boot=casper nopersistent toram quiet splash ---
   initrd /casper/initrd
}

menuentry "Install Ubuntu FS" {
   linux /casper/vmlinuz boot=casper only-ubiquity quiet splash ---
   initrd /casper/initrd
}

menuentry "Check disc for defects" {
   linux /casper/vmlinuz boot=casper integrity-check quiet splash ---
   initrd /casper/initrd
}

menuentry "Test memory Memtest86+ (BIOS)" {
   linux16 /install/memtest86+
}

menuentry "Test memory Memtest86 (UEFI, long load time)" {
   insmod part_gpt
   insmod search_fs_uuid
   insmod chain
   loopback loop /install/memtest86
   chainloader (loop,gpt1)/efi/boot/BOOTX64.efi
}
EOF

Create manifest

Next we create a file filesystem.manifest to specify each package and it's version that is installed on the live system. We create another file filesystem.manifest-desktop which specifies which files will be installed on the target system. Once the Ubiquity installer completes, it will remove packages specified in filesystem.manifest that are not listed in filesystem.manifest-desktop.

  1. Access build directory

    cd $HOME/live-ubuntu-from-scratch

  2. Generate manifest

    sudo chroot chroot dpkg-query -W --showformat='${Package} ${Version}\n' | sudo tee image/casper/filesystem.manifest

sudo cp -v image/casper/filesystem.manifest image/casper/filesystem.manifest-desktop

sudo sed -i '/ubiquity/d' image/casper/filesystem.manifest-desktop

sudo sed -i '/casper/d' image/casper/filesystem.manifest-desktop

sudo sed -i '/discover/d' image/casper/filesystem.manifest-desktop

sudo sed -i '/laptop-detect/d' image/casper/filesystem.manifest-desktop

sudo sed -i '/os-prober/d' image/casper/filesystem.manifest-desktop

Compress the chroot

After everything has been installed and preconfigured in the chrooted environment, we need to generate an image of everything that was done by following the next steps in the build environment.

  1. Access build directory

    cd $HOME/live-ubuntu-from-scratch

  2. Create squashfs

    sudo mksquashfs chroot image/casper/filesystem.squashfs

    Squashfs is a highly compressed read-only filesystem for Linux. It uses zlib compression to compress both files, inodes and directories. Inodes in the system are very small and all blocks are packed to minimize data overhead. Block sizes greater than 4K are supported up to a maximum of 64K. Squashfs is intended for general read-only filesystem use, for archival use (i.e. in cases where a .tar.gz file may be used), and in constrained block device/memory systems (e.g. embedded systems) where low overhead is needed.

  3. Write the filesystem.size

    printf $(sudo du -sx --block-size=1 chroot | cut -f1) > image/casper/filesystem.size

Create diskdefines

README file often found on Linux LiveCD installer discs, such as an Ubuntu Linux installation CD; typically named “README.diskdefines” and may be referenced during installation.

  1. Access build directory

    cd $HOME/live-ubuntu-from-scratch

  2. Create file image/README.diskdefines

    cat <<EOF > image/README.diskdefines
#define DISKNAME  Ubuntu from scratch
#define TYPE  binary
#define TYPEbinary  1
#define ARCH  amd64
#define ARCHamd64  1
#define DISKNUM  1
#define DISKNUM1  1
#define TOTALNUM  0
#define TOTALNUM0  1
EOF

Create ISO Image for a LiveCD (BIOS + UEFI)

  1. Access image directory

    cd $HOME/live-ubuntu-from-scratch/image

  2. Create a grub UEFI image

    grub-mkstandalone \
   --format=x86_64-efi \
   --output=isolinux/bootx64.efi \
   --locales="" \
   --fonts="" \
   "boot/grub/grub.cfg=isolinux/grub.cfg"

  3. Create a FAT16 UEFI boot disk image containing the EFI bootloader

    (
   cd isolinux && \
   dd if=/dev/zero of=efiboot.img bs=1M count=10 && \
   sudo mkfs.vfat efiboot.img && \
   LC_CTYPE=C mmd -i efiboot.img efi efi/boot && \
   LC_CTYPE=C mcopy -i efiboot.img ./bootx64.efi ::efi/boot/
)

  4. Create a grub BIOS image

    grub-mkstandalone \
   --format=i386-pc \
   --output=isolinux/core.img \
   --install-modules="linux16 linux normal iso9660 biosdisk memdisk search tar ls" \
   --modules="linux16 linux normal iso9660 biosdisk search" \
   --locales="" \
   --fonts="" \
   "boot/grub/grub.cfg=isolinux/grub.cfg"

  5. Combine a bootable Grub cdboot.img

    cat /usr/lib/grub/i386-pc/cdboot.img isolinux/core.img > isolinux/bios.img

  6. Generate md5sum.txt

    sudo /bin/bash -c "(find . -type f -print0 | xargs -0 md5sum | grep -v -e 'md5sum.txt' -e 'bios.img' -e 'efiboot.img' > md5sum.txt)"

  7. Create iso from the image directory using the command-line

    sudo xorriso \
   -as mkisofs \
   -iso-level 3 \
   -full-iso9660-filenames \
   -volid "Ubuntu from scratch" \
   -output "../ubuntu-from-scratch.iso" \
   -eltorito-boot boot/grub/bios.img \
      -no-emul-boot \
      -boot-load-size 4 \
      -boot-info-table \
      --eltorito-catalog boot/grub/boot.cat \
      --grub2-boot-info \
      --grub2-mbr /usr/lib/grub/i386-pc/boot_hybrid.img \
   -eltorito-alt-boot \
      -e EFI/efiboot.img \
      -no-emul-boot \
   -append_partition 2 0xef isolinux/efiboot.img \
   -m "isolinux/efiboot.img" \
   -m "isolinux/bios.img" \
   -graft-points \
      "/EFI/efiboot.img=isolinux/efiboot.img" \
      "/boot/grub/bios.img=isolinux/bios.img" \
      "."

Alternative way, if previous one fails, create an Hybrid ISO

  1. Create a ISOLINUX (syslinux) boot menu

    cat <<EOF> 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 Try Ubuntu FS
 MENU DEFAULT
 KERNEL /casper/vmlinuz
 APPEND initrd=/casper/initrd boot=casper

LABEL linux
 MENU LABEL Try Ubuntu FS (nomodeset)
 MENU DEFAULT
 KERNEL /casper/vmlinuz
 APPEND initrd=/casper/initrd boot=casper nomodeset
EOF

  2. Include syslinux bios modules

    apt install -y syslinux-common && \
cp /usr/lib/ISOLINUX/isolinux.bin isolinux/ && \
cp /usr/lib/syslinux/modules/bios/* isolinux/

  3. Create iso from the image directory

    sudo xorriso \
   -as mkisofs \
   -iso-level 3 \
   -full-iso9660-filenames \
   -volid "Ubuntu from scratch" \
   -output "../ubuntu-from-scratch.iso" \
 -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 /EFI/boot/efiboot.img \
     -no-emul-boot \
     -isohybrid-gpt-basdat \
 -append_partition 2 0xef EFI/boot/efiboot.img \
   "$HOME/live-ubuntu-from-scratch/image"

Make a bootable USB image

It is simple and easy, using "dd"

sudo dd if=ubuntu-from-scratch.iso of=<device> status=progress oflag=sync

Summary

This completes the process of creating a live Ubuntu installer from scratch. The generated ISO may be tested in a virtual machine such as VirtualBox or written to media and booted from a standard PC.

Contributing

Please read CONTRIBUTING.md for details on our code of conduct, and the process for submitting pull requests to us.

Versioning

We use GitHub for versioning. For the versions available, see the tags on this repository.

License

This project is licensed under the GNU GENERAL PUBLIC LICENSE - see the LICENSE file for details