AlmaLinux Wiki

# Using Generic Cloud Images on a local machine

You can use the AlmaLinux OS 8 and 9 Generic Cloud images for testing, developing, manipulating and repackaging purposes on your local machine.

Required packages:

  • osinfo-db for AlmaLinux OS support on the virtualization stack.
  • qemu-img (RPM) (ArchLinux), qemu-utils (DEB) for creating snapshots.
  • virt-install (CLI) virt-manager (GUI) (RPM), virt-manager (ships with virt-install too) (DEB) for creating VMs.
  • xorriso or genisoimage for creation of Cloud-init data ISOs.
  • guestfs-tools (RPM) (ArchLinux), libguestfs-tools (DEB) for inspecting and manipulating image content.

# AlmaLinux Guest OS support

You need at least version 20210215 for AlmaLinux and 20210426 for other distributions osinfo-db packages to support AlmaLinux as a guest OS.

TIP

20210621 and newer recommended for latest improvements.

To check whether AlmaLinux OS is supported on the installed version of osinfo-db:

osinfo-query os | grep almalinux

 almalinux8           | AlmaLinux 8                                        | 8        | http://almalinux.org/almalinux/8
 almalinux9           | AlmaLinux 9                                        | 9        | http://almalinux.org/almalinux/9

If the installed osinfo-db doesn’t support either or any version of AlmaLinux OS, You can manually update the Osinfo database with the --local option without overriding the installed osinfo-db which is installed by the distribution's package manager. The new database will have precedence when the database is loaded.

Retrieve the latest $osinfo_db_version from here (e.g., 20230719) : https://releases.pagure.org/libosinfo/?C=M;O=D (opens new window)

osinfo_db_version='20230719' # Replace with the latest version

curl -O https://releases.pagure.org/libosinfo/osinfo-db-"$osinfo_db_version".tar.xz # Download
sudo osinfo-db-import --local osinfo-db-"$osinfo_db_version".tar.xz # Install

Refer to this guide to download and verify the cloud images: https://wiki.almalinux.org/cloud/Generic-cloud.html#download-and-verification (opens new window)

# Create a snapshot from the image

If you don’t want to modify the cloud image each time you create a VM, you can create a snapshot from the cloud image. The snapshot's virtual size can be different from the base image. In this example, we will use 20G instead of the base image's virtual size (10G). Cloud-init will grow the root filesystem automatically on the creation of the VM.

qemu-img create -f qcow2 -b AlmaLinux-9-GenericCloud-9.2-20230513.x86_64.qcow2 -F qcow2 wiki_example_almalinux92_snapshot.qcow2 20G

WARNING

If you face a permission error on image, snapshot, and Cloud-init ISO files, you can resolve it in the following ways:

  • You can move the image and snapshot to the /var/lib/libvirt/images directory.
  • Change the ownership of file to qemu user with chown qemu:qemu. On SELinux enforced systems, do not forget to change the context type too with chcon -t virt_image_t

# Cloud-init

The NoCloud (opens new window) datasource allows the user to provide user-data, meta-data and network-config to the VM without running a network service (or even without having a network at all). You can provide Meta-data and User-data files with --cloud-init option of virt-install (opens new window) >= 3.0.0 or with an ISO file for versions `< 3.0.0.

The name of the default user on the AlmaLinux OS Generic Cloud images is almalinux and it's locked. Therefore we need to inject a password or public ssh key for authentication. In this example, we do both: set a password and add public SSH keys for the almalinux user.

These two main criteria must be met on the Cloud-init User Data:

  • The first line must be #cloud-config.
  • The syntax must be in YAML.

user-data:

#cloud-config

ssh_pwauth: true # sshd service will be configured to accept password authentication method
password: changeme # Set a password for almalinux
chpasswd:
    expire: false # Don't ask for password reset after the first log-in
ssh_authorized_keys: # Add your ssh public key for publickey authentication
    - ssh-ed25519 AAAAB3NzaC1yc2EAAAABIwAAAQEA3I7VUf2l5gSn5uavROsc5HRDpZ turquoisekodkod@almalinux.example
    - ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAGEA3FSyQwBI6Z+nCSjUU sapphirecaracal@almalinux.example

TIP

Refer to the Cloud-init modules list (opens new window) for further customization options.

TIP

You can close the console output of the VM with Ctrl + ]

Start the VM - virt-install >= 3.0.0 with --cloud-init option:

#!/usr/bin/env bash


vm_name='wiki-example-almalinux92'
vm_memory='2048'
vm_cpus='2'
vm_disk='/var/lib/libvirt/images/wiki_example_almalinux92_snapshot.qcow2'

ci_user_data='ci_user_data_ssh_auth_pass_pubkey'


virt-install \
    --connect qemu:///system \
    --name "$vm_name" \
    --memory "$vm_memory" \
    --machine q35 \
    --vcpus "$vm_cpus" \
    --cpu host-passthrough \
    --import \
    --cloud-init user-data="$ci_user_data" \
    --osinfo name=almalinux8 \
    --disk "$vm_disk" \
    --virt-type kvm

Start the VM - virt-install < 3.0.0

Create Cloud-init data ISO with User and Meta data files:

WARNING

The filename of Cloud-init user data, meta data must be renamed to user-data and meta-data and be placed on the root directory of ISO.

/user-data
/meta-data

The meta-data can be empty for no meta-data option

touch meta-data

xorriso (AlmaLinux OS 9)

xorriso -as genisoimage -output ci_data.iso -volid CIDATA -joliet -rock user-data meta-data

genisoimage (AlmaLinux OS 8)

genisoimage -output ci_data.iso -volid CIDATA -joliet -rock user-data meta-data

Create the VM with Cloud-init data ISO mounted:

#!/usr/bin/env bash

vm_name='wiki-almalinux92'
vm_memory='2048'
vm_cpus='2'
vm_disk='/var/lib/libvirt/images/wiki_example_almalinux92_snapshot.qcow2'

ci_dataiso='/var/lib/libvirt/images/ci_data.iso'

virt-install \
     --connect qemu:///system \
     --name "$vm_name" \
     --memory "$vm_memory" \
     --machine q35 \
     --vcpus $vm_cpus \
     --cpu host-passthrough \
     --import \
     --osinfo name=almalinux9 \
     --disk "$vm_disk" \
     --disk "$ci_dataiso",device=cdrom \
     --virt-type kvm

Get the IP address of the VM:

virsh domainifaddr $VM_NAME

# Static IP

To create a VM with static IPs rather than dynamic from DHCP, We need to create network-config file in Networking config Version 1 or Networking config Version 2 format.

An example for a single interface VM on 192.168.122.0/24 network, our network-config file would be:

Networking config Version 1:

version: 1
config:
  - type: physical
    name: eth0
    subnets:
      - type: static
        address: 192.168.122.92
        netmask: 255.255.255.0
        gateway: 192.168.122.1
        dns_nameservers:
          - 192.168.122.1
          - 9.9.9.9

Networking config Version 2:

version: 2
ethernets:
  eth0:
    addresses:
      - 192.168.122.92/24
    gateway4: 192.168.124.1
    nameservers:
      addresses:
        - 192.168.122.1
        - 9.9.9.9

TIP

Please consult documenation pages of Networking config Version 1 (opens new window) and Networking config Version 2 (opens new window) for the full list of options.

In virt-install/manager version >= 4.1.0 (available in AlmaLinux OS 9), you can use the network-config sub-option of the --cloud-init option.

#!/usr/bin/env bash

vm_name='wiki-almalinux92'
vm_memory='2048'
vm_cpus='2'
vm_disk='/var/lib/libvirt/images/wiki_example_almalinux92_snapshot.qcow2'

ci_user_data='ci_user_data_ssh_auth_pass_pubkey' # Cloud-init user-data
ci_network_config='ci_network_config_192_168_122_92_v1' # Cloud-init network-config


virt-install \
     --connect qemu:///system \
     --name "$vm_name" \
     --memory "$vm_memory" \
     --machine q35 \
     --vcpus "$vm_cpus" \
     --cpu host-passthrough \
     --import \
     --cloud-init user-data="$ci_user_data",network-config="$ci_network_config" \
     --osinfo name=almalinux9 \
     --disk "$vm_disk" \
     --virt-type kvm

On virt-install/manager < 4.1.0 (AlmaLinux OS 8), you will need to create a Cloud-init Data ISO in ISO 9660 format.

WARNING

The names of Cloud-init user data, meta data and networking config must be renamed to user-data, meta-data and network-config and be present on the root directory of ISO.

/user-data
/meta-data
/network-config

Create the Cloud-init Data ISO:

The meta-data file can be empty if no meta-data is needed.

touch meta-data

xorriso (AlmaLinux OS 9)

xorriso -as genisoimage -output ci_data.iso -volid CIDATA -joliet -rock user-data meta-data network-config

genisoimage (AlmaLinux OS 8)

genisoimage -output ci_data.iso -volid CIDATA -joliet -rock user-data meta-data network-config

Create the VM with Cloud-init data ISO mounted:

#!/usr/bin/env bash

vm_name='wiki-almalinux92'
vm_memory='2048'
vm_cpus='2'
vm_disk='/var/lib/libvirt/images/wiki_example_almalinux92_snapshot.qcow2'

ci_dataiso='/var/lib/libvirt/images/ci_data.iso'

virt-install \
     --connect qemu:///system \
     --name "$vm_name" \
     --memory "$vm_memory" \
     --machine q35 \
     --vcpus $vm_cpus \
     --cpu host-passthrough \
     --import \
     --osinfo name=almalinux9 \
     --disk "$vm_disk" \
     --disk "$ci_dataiso",device=cdrom \
     --virt-type kvm

# Virt-Manager (GUI)

Unlike the virt-install, the virt-manager doesn't have an option to provide Cloud-init user-data, meta-data and network-config (Static IP). For that reason we can add Cloud-init data ISO to our VM as CDROM device.

"New VM" -> "Import existing disk image" -> Choose AlmaLinux OS image itself or snapshot, put a tick on the "Customize configuration before install" option.

"Add Hardware" -> "Storage" -> Select Device type as "CDROM", click on "Manage" and select Cloud-init data ISO and click on "Finish" button. Start the VM with the "Begin Installation".

# Repackage cloud image

shutdown VM:

sudo virsh shutdown $VM_NAME

Convert the snapshot to the full image without touching backing file(AlmaLinux-8-GenericCloud-8.4-20210616.x86_64.qcow2):

qemu-img convert -c -O qcow2 doc-almalinux84-snapshot.qcow2 doc-almalinux84-base.qcow2

You can reset, unconfigure and inject files to the image with libguestfs virt-sysprep. See the upstream documentation for further option (opens new window) and operations. (opens new window)

virt-sysprep --format qcow2 -a doc-almalinux84-base.qcow2

# Inspection and Manipulation of images

Show a file inside the image

virt-cat -a AlmaLinux-9-GenericCloud-9.2-20230513.x86_64.qcow2 /etc/cloud/cloud.cfg

Show disk usage inside the image

virt-df -a AlmaLinux-9-GenericCloud-9.2-20230513.x86_64.qcow2 -h

Display the OS infromation

virt-inspector -a AlmaLinux-9-GenericCloud-9.2-20230513.x86_64.qcow2

Get the version of kernel package with the help of XPATH query

virt-inspector -a AlmaLinux-9-GenericCloud-9.2-20230513.x86_64.qcow2 | virt-inspector --xpath '//application[name="kernel"]/version | //application[name="kernel"]/release'

<version>5.14.0</version>
<release>284.11.1.el9_2</release>

Mount filesystems of an image.

mkdir guest_mount # Create the mount directoy
guestmount -a AlmaLinux-9-GenericCloud-9.2-20230513.x86_64.qcow2 -i --ro guest_mount/ # Mount read-only with --ro
guestunmount guest-mount/ # Unmount

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You can check the libguestfs's website (opens new window) for more documentation and more tools

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