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

1. Access build directory

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

2. Create empty virtual hard drive file (30Gb)

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

3. 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

4. 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
   

5. 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

1. 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
   

2. 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

1. Access build directory

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

2. Create chroot directory

   mkdir chroot

3. Mount root partition

   sudo mount /dev/loop18p2 chroot/

4. 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

1. Access chroot environment

   sudo chroot $HOME/cloud-image-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-image" > /etc/hostname

4. 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

5. 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

6. Update indexes packages

   apt-get update

7. 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.

8. 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.

9. 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”

      

10. 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

11. Reconfigure packages

    1. Generate locales

       dpkg-reconfigure locales

       1. Select locales

          

       2. Select default locale

          

    2. Configure network-manager

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

    3. Reconfigure network-manager

       dpkg-reconfigure network-manager

12. Install grub

    1. Install

       grub-install /dev/loop0

       A similar output to this

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

    2. 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
       

    3. Update packages

       apt-get -y upgrade

VirtualBox

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

1. 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

2. Mount ISO

   mount -o loop VBoxGuestAdditions_6.1.38.iso /mnt

3. 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
   

4. 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.
   

5. Umount and remove ISO

   umount /mnt
   
   rm -rf VBoxGuestAdditions_6.1.38.iso

6. 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

1. Install the latest package version

   apt-get install walinuxagent

2. 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
   

3. To enable run:

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

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/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

1. Convert raw image to qcow2

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

2. 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

3. Create a simple meta-data intilizer cloud-init

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

4. 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)
   

5. Launch virtual machine

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

6. 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