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README.md

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.

Prerequisites (GNU/Linux Debian/Ubuntu)

Install applications we need to build the environment.

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

  • 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

  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 \
        ubuntu-standard \
        casper \
        lupin-casper \
        discover \
        laptop-detect \
        os-prober \
        network-manager \
        resolvconf \
        net-tools \
        wireless-tools \
        wpagui \
        locales \
        linux-generic
    

    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 grub

    2. Don’t select any options

    3. Only confirm “Yes”

  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

    2. 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)

    1. 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
      
    2. Then update the package cache and install the package using

      apt-get update
      
      apt-get install -y code
      
  14. Install Google Chrome (optional)

    1. 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
      
    2. Then update the package cache and install the package using

      apt-get update
      
      apt-get install google-chrome-stable
      
  15. Install Java JDK 8 (optional)

    apt-get install -y \
        openjdk-8-jdk \
        openjdk-8-jre
    
  16. Remove unused applications (optional)

    apt-get purge -y \
        transmission-gtk \
        transmission-common \
        gnome-mahjongg \
        gnome-mines \
        gnome-sudoku \
        aisleriot \
        hitori
    
  17. Remove unused packages

    apt-get autoremove -y
    
  18. Reconfigure packages

    1. Generate locales

      dpkg-reconfigure locales
      
      1. Select locales

      2. Select default locale

    2. Reconfigure resolvconf

      dpkg-reconfigure resolvconf
      
      1. Confirm changes

    3. Configure network-manager

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

      dpkg-reconfigure network-manager
      
  19. Cleanup the chroot environment

    1. If you installed software, be sure to run

      truncate -s 0 /etc/machine-id
      
    2. Remove the diversion

      rm /sbin/initctl
      
      dpkg-divert --rename --remove /sbin/initctl
      
    3. 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

  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 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

In the next steps the creation of the manifest is important because it tells us which version of each package installed in the Live version and which packages will be removed or maintained in the version that will be installed (persisted in the hard drive).

  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.

  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" \
       -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 \
       -output "../ubuntu-from-scratch.iso" \
       -m "isolinux/efiboot.img" \
       -m "isolinux/bios.img" \
       -graft-points \
          "/EFI/efiboot.img=isolinux/efiboot.img" \
          "/boot/grub/bios.img=isolinux/bios.img" \
          "."
    

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