How to create a Cloud image Ubuntu from scratch

This procedure shows how to create a cloud image Ubuntu from scratch to run on Cloud environments (EC2, GCE, Azure, QEMU, OpenStack and VirtualBox).

Prerequisites (GNU/Linux Debian/Ubuntu)

Install applications we need to build the environment.

sudo apt-get install \
   debootstrap \
   qemu-utils \
   qemu-system \
   genisoimage

mkdir $HOME/cloud-image-ubuntu-from-scratch

Create loop device

Access build directory

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

Create empty virtual hard drive file (30Gb)

dd if=/dev/zero of=cloud-ubuntu-image.raw bs=1 count=0 seek=32212254720 status=progress

Create partitions on file

sed -e 's/\s*\([\+0-9a-zA-Z]*\).*/\1/' << EOF | sudo fdisk cloud-ubuntu-image.raw
o # clear the in memory partition table
n # new partition
p # primary partition
1 # partition number 1 
    # default - start at beginning of disk
+512M # 512 MB boot parttion
n # new partition
p # primary partition
2 # partion number 2
    # default, start immediately after preceding partition
    # default, extend partition to end of disk
a # make a partition bootable
1 # bootable partition is partition 1 -- /dev/loop0p1
p # print the in-memory partition table
w # write the partition table
q # and we're done
EOF

Start loop device

sudo losetup --show -fP cloud-ubuntu-image.raw

A similar output to this

/dev/loop18

Check loop device

sudo losetup -l /dev/loop18

A similar output to this

NAME        SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE                                                            DIO LOG-SEC
/dev/loop18         0      0         0  0 /home/scratch/cloud-image-ubuntu-from-scratch/cloud-ubuntu-image.raw   0     512

Check partitions on loop device

sudo fdisk -l /dev/loop18

A similar output to this

Disk /dev/loop18: 30 GiB, 32212254720 bytes, 62914560 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x64e50bc1

Device        Boot   Start      End  Sectors  Size Id Type
/dev/loop18p1 *       2048  1050623  1048576  512M 83 Linux
/dev/loop18p2      1050624 62914559 61863936 29.5G 83 Linux

Format partitions loop device

Format device loop0p1 (/boot)

sudo mkfs.ext4 /dev/loop18p1

A similar output to this

mke2fs 1.47.0 (5-Feb-2023)
Discarding device blocks: done                            
Creating filesystem with 131072 4k blocks and 32768 inodes
Filesystem UUID: 08b9e410-eb6d-4ba7-8a83-c3c960bca98c
Superblock backups stored on blocks: 
	32768, 98304
      
Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

Format device loop0p2 (/)

sudo mkfs.ext4 /dev/loop18p2

A similar output to this

mke2fs 1.47.0 (5-Feb-2023)
Discarding device blocks: done                            
Creating filesystem with 7732992 4k blocks and 1933312 inodes
Filesystem UUID: 1c8f95b7-ea0f-4b62-a6ca-2da0c42209e2
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
	4096000
      
Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done   

Mount loop devices

Access build directory

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

Create chroot directory
```
mkdir chroot
```
Mount root partition
```
sudo mount /dev/loop18p2 chroot/
```
Mount boot partition

First you need create directory…
```
sudo mkdir chroot/boot
```
… and mount boot partition
```
sudo mount /dev/loop18p1 chroot/boot
```

Bootstrap and Configure Ubuntu

Checkout bootstrap

sudo debootstrap \
   --arch=amd64 \
   --variant=minbase \
   --components "main,universe" \
   --include "ca-certificates,cron,iptables,isc-dhcp-client,libnss-myhostname,ntp,ntpdate,rsyslog,ssh,sudo,dialog,whiptail,man-db,curl,dosfstools,e2fsck-static" \
   bionic \
   $HOME/cloud-image-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/cloud-image-ubuntu-from-scratch/chroot/dev
  
sudo mount --bind /run $HOME/cloud-image-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/cloud-image-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-image" > /etc/hostname
```

Configure apt sources.list

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

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

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

Configure fstab

cat <<EOF > /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system>         <mount point>   <type>  <options>                       <dump>  <pass>
/dev/sda2               /               ext4    errors=remount-ro               0       1
/dev/sda1               /boot           ext4    defaults                        0       2
EOF

Update indexes packages
```
apt-get update
```
Install systemd
```
apt-get install -y 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.
Install packages needed for system
```
apt-get install -y \
    os-prober \
    ifupdown \
    network-manager \
    locales \
    build-essential \
    module-assistant \
    cloud-init \
    grub-pc \
    grub2 \
    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”

Configure interfaces

cat <<EOF > /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback
EOF

Reconfigure packages

Generate locales
```
dpkg-reconfigure locales
```
1. Select locales
2. Select default locale

Configure network-manager

cat <<EOF > /etc/NetworkManager/NetworkManager.conf
[main]
rc-manager=none
plugins=ifupdown,keyfile
dns=systemd-resolved
      
[ifupdown]
managed=false
EOF

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

Install grub

Install

grub-install /dev/loop0

A similar output to this

Installing for i386-pc platform.
Installation finished. No error reported.

Update grub configuration

update-grub

A similar output to this

Sourcing file `/etc/default/grub'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.15.0-74-generic
Found initrd image: /boot/initrd.img-4.15.0-74-generic
Adding boot menu entry for EFI firmware configuration
done

Update packages
```
apt-get -y upgrade
```

VirtualBox

If you plan to use this image in VirtualBox, install VirtualBox Guest Additions

Download VirtualBox Guest Additions

 curl --progress-bar https://download.virtualbox.org/virtualbox/6.1.38/VBoxGuestAdditions_6.1.38.iso -o VBoxGuestAdditions_6.1.38.iso

Mount ISO

 mount -o loop VBoxGuestAdditions_6.1.38.iso /mnt

Install

 /mnt/VBoxLinuxAdditions.run --nox11

Output like this

 Verifying archive integrity... All good.
 Uncompressing VirtualBox 6.1.38 Guest Additions for Linux........
 VirtualBox Guest Additions installer
 Copying additional installer modules ...
 Installing additional modules ...
 depmod: ERROR: could not open directory /lib/modules/4.19.0-6-amd64: No such file or directory
 depmod: FATAL: could not search modules: No such file or directory
 VirtualBox Guest Additions: Starting.
 VirtualBox Guest Additions: Building the VirtualBox Guest Additions kernel 
 modules.  This may take a while.
 VirtualBox Guest Additions: To build modules for other installed kernels, run
 VirtualBox Guest Additions:   /sbin/rcvboxadd quicksetup <version>
 VirtualBox Guest Additions: or
 VirtualBox Guest Additions:   /sbin/rcvboxadd quicksetup all
 VirtualBox Guest Additions: Kernel headers not found for target kernel 
 4.19.0-6-amd64. Please install them and execute
   /sbin/rcvboxadd setup
 modprobe vboxguest failed
 The log file /var/log/vboxadd-setup.log may contain further information.
 Running in chroot, ignoring request: daemon-reload

Generate modules inside chroot environment

 ls -al /lib/modules

Output

 total 12
 drwxr-xr-x  3 root root 4096 Jan 25 22:29 .
 drwxr-xr-x 14 root root 4096 Jan 25 22:29 ..
 drwxr-xr-x  5 root root 4096 Jan 25 22:29 4.15.0-74-generic

Use the same name listed before 4.15.0-74-generic

 rcvboxadd quicksetup 4.15.0-74-generic

Output like this

 VirtualBox Guest Additions: Building the modules for kernel 4.15.0-74-generic.
 update-initramfs: Generating /boot/initrd.img-4.15.0-74-generic
 Warning: /sbin/fsck.vfat doesn't exist, can't install to initramfs, ignoring.

Umount and remove ISO

 umount /mnt

 rm -rf VBoxGuestAdditions_6.1.38.iso

Fix vboxadd-service

 sed -i -e 's/ systemd-timesyncd.service//g' /lib/systemd/system/vboxadd-service.service

Azure

If you plan to use this image in Azure, install the Azure agent

Install the latest package version
```
 apt-get install walinuxagent
```
Ensure auto update is enabled

First, check to see if it is enabled:
```
 cat /etc/waagent.conf | grep AutoUpdate.Enabled
```
Find ‘AutoUpdate.Enabled’. If you see this output, it is enabled:
```
 # AutoUpdate.Enabled=y
```

To enable run:

 sudo sed -i 's/# AutoUpdate.Enabled=n/AutoUpdate.Enabled=y/g' /etc/waagent.conf

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/cloud-image-ubuntu-from-scratch/chroot/dev

sudo umount $HOME/cloud-image-ubuntu-from-scratch/chroot/run

Umount loop partitions

sudo umount $HOME/cloud-image-ubuntu-from-scratch/chroot/boot

sudo umount $HOME/cloud-image-ubuntu-from-scratch/chroot

Leave loop device

sudo losetup -D

Conclusion

At the end the image produced is in cloud-ubuntu-image.raw.

Now you can use this raw image and import it into your favorite cloud.

Each cloud has a process for importing which we will not deal with here.

Test image

Convert raw image to qcow2

qemu-img convert -f raw cloud-ubuntu-image.raw -O qcow2 ubuntu-image.qcow2

Create a simple user-data intilizer cloud-init

Generate hash passwd ‘ubuntu’

openssl passwd -6 ubuntu

Output

$6$vcSilJc5EkAaj/sE$RfHgGqzKQ/iVHvFObi8acrKFeLUcNAHH7YPT7hP7euIB5m8p.rbxxntrgyFalFG6eKlKE/OLCq6L2Fu/NWZi4/

Use this value on user-data yml file

cat <<EOF > user-data
#cloud-config

users:
- name: ubuntu
  passwd: \$6\$vcSilJc5EkAaj/sE\$RfHgGqzKQ/iVHvFObi8acrKFeLUcNAHH7YPT7hP7euIB5m8p.rbxxntrgyFalFG6eKlKE/OLCq6L2Fu/NWZi4/
  lock_passwd: false
  sudo: ['ALL=(ALL) NOPASSWD:ALL']
  shell: /bin/bash

power_state:
  mode: reboot
  timeout: 30
  condition: true
EOF

Create a simple meta-data intilizer cloud-init

cat <<EOF > meta-data
local-hostname: instance-test
EOF

Create a disk to attach with Cloud-Init configuration

genisoimage \
   -output instance-test-cidata.iso \
   -input-charset utf-8 \
   -volid cidata \
   -joliet \
   -rock \
   user-data meta-data

Output

Total translation table size: 0
Total rockridge attributes bytes: 331
Total directory bytes: 0
Path table size(bytes): 10
Max brk space used 0
183 extents written (0 MB)

Launch virtual machine

qemu-system-x86_64 \
   -m 512 \
   -hda ubuntu-image.qcow2 \
   -cdrom instance-test-cidata.iso \
   -enable-kvm \
   -net nic \
   -net user

Login on image

Use user ubuntu and password ubuntu, previously configured in step 2

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.

Authors

Marcos Vallim - Initial work, Development, Test, Documentation - mvallim

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

License

This project is licensed under the Apache License - see the LICENSE file for details