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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.

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

Access chroot environment

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

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.
Set a custom hostname
```
echo "ubuntu-fs-live" > /etc/hostname
```

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

Update indexes packages
```
apt-get update
```
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.
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.
Upgrade packages
```
apt-get -y upgrade
```

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.

Configure grub
Don’t select any options
Only confirm “Yes”

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

Install window manager

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

Install useful applications

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

Install Visual Studio Code (optional)

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

Then update the package cache and install the package using
```
apt-get update

apt-get install -y code
```

Install Google Chrome (optional)

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

Then update the package cache and install the package using
```
apt-get update

apt-get install google-chrome-stable
```

Install Java JDK 8 (optional)

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

Remove unused applications (optional)

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

Remove unused packages
```
apt-get autoremove -y
```

Reconfigure packages

Generate locales
```
dpkg-reconfigure locales
```
1. Select locales
2. Select default locale
Reconfigure resolvconf
```
dpkg-reconfigure resolvconf
```
1. Confirm changes

Configure network-manager

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

[ifupdown]
managed=false
EOF

Reconfigure network-manager
```
dpkg-reconfigure network-manager
```

Cleanup the chroot environment

If you installed software, be sure to run
```
truncate -s 0 /etc/machine-id
```

Remove the diversion

rm /sbin/initctl

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

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

Access build directory
```
cd $HOME/live-ubuntu-from-scratch
```

Create directories

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

Copy kernel images

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

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

Copy memtest86+ binary (BIOS)

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

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

Access build directory
```
cd $HOME/live-ubuntu-from-scratch
```
Create base point access file for grub
```
touch image/ubuntu
```

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).

Access build directory
```
cd $HOME/live-ubuntu-from-scratch
```

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.

Access build directory
```
cd $HOME/live-ubuntu-from-scratch
```
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.

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.

Access build directory
```
cd $HOME/live-ubuntu-from-scratch
```

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)

Access image directory

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

Create a grub UEFI image

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

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/
)

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"

Combine a bootable Grub cdboot.img

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

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)"

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

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