305-300 LPIC-3: Virtualization and Containerization - Exam 305, version 3.0 Questions and Answers

Libvirt supports creating and managing various types of virtual networks that can be used to connect virtual machines to each other or to the external network. One of the common types of virtual networks is the NAT-based network, which uses network address translation (NAT) to allow virtual machines to access the outside world through the host’s network interface. By default, libvirt creates a NAT-based network called ‘default’ when it is installed and started. This network appears as a standard Linux bridge device on the host system, named virbr0. The bridge device has an IP address of 192.168.122.1/24 and acts as a gateway and a DHCP server for the virtual machines connected to it. The bridge device also has iptables rules to forward and masquerade the traffic from and to the virtual machines. The virtual machines connected to the ‘default’ network have their own IP addresses in the 192.168.122.0/24 range and their own MAC addresses generated by libvirt. The virtual machines can communicate with each other, with the host, and with the external network through the bridge device and the NAT mechanism12.

The other statements in the question are false regarding networking with libvirt. Libvirt’s network functionality is not limited to connecting virtual machines to a physical network interface of the host system. Libvirt can also create isolated networks that do not have any connection to the outside world, or routed networks that use static routes to connect virtual machines to the external network without NAT3. Libvirt does not assign the same MAC address to all virtual machines and isolate their network interfaces at the link layer. Libvirt assigns a unique MAC address to each virtual machine and allows them to communicate with each other at the network layer4. Libvirt does not require a dedicated network interface that may not be used by the host system. Libvirt can share the host’s network interface with the virtual machines using NAT or bridging, or it can pass a physical network interface to a virtual machine exclusively using PCI passthrough5. Libvirt does not support exactly one virtual network and connect all virtual machines to it. Libvirt supports creating and managing multiple virtual networks with different names and configurations, and connecting virtual machines to different networks according to their needs6. References:

libvirt: Virtual Networking

libvirt: NAT forwarding (aka “virtual networks”)

libvirt: Routed network

libvirt: MAC address

libvirt: PCI passthrough of host network devices

[libvirt: Network XML format]

The subcommand of virsh that opens the XML configuration of a virtual network in an editor in order to make changes to that configuration is net-edit1. This subcommand takes the name or UUID of the network as a parameter and opens the network XML file in the default editor, which is specified by the $EDITOR shell variable1. The changes made to the network configuration are applied immediately after saving and exiting the editor1.

References:

1: net-edit - libvirt.

In an IaaS cloud, the most common method for provisioning new computing instances is to use an image file that contains a pre-installed operating system and software. This image file is also known as a machine image, a virtual appliance, or a template. The image file can be customized for a specific purpose, such as a web server, a database server, or a development environment. The image file can be stored in a repository or a library that is accessible by the cloud provider or the user. When a new instance is requested, the cloud provider copies the image file to a virtual disk and attaches it to the instance. The instance then boots from the virtual disk and runs the operating system and software from the image file. This method is faster and more efficient than installing the operating system and software from scratch for each new instance. It also ensures consistency and reliability across multiple instances that use the same image file. References:

LPI Virtualization and Containerization Exam Objectives, Topic 305.1: Virtualization Concepts and Theory, Objective: Describe the concept of machine images and templates

LPI Virtualization and Containerization Study Guide, Chapter 1: Virtualization Concepts and Theory, Section: Machine Images and Templates

LPI LPIC-3 305 Certification Sample Questions and Practice Exam, Question 10: In an IaaS cloud, what is a common method for provisioning new computing instances with an operating system and software?

The purpose of the packer inspect subcommand is to display an overview of the configuration contained in a Packer template1. A Packer template is a file that defines the various components a Packer build requires, such as variables, sources, provisioners, and post-processors2. The packer inspect subcommand can help you quickly learn about a template without having to dive into the HCL (HashiCorp Configuration Language) itself1. The subcommand will tell you things like what variables a template accepts, the sources it defines, the provisioners it defines and the order they’ll run, and more1.

The other options are not correct because:

A) Retrieve files from an existing Packer image. This is not the purpose of the packer inspect subcommand. To retrieve files from an existing Packer image, you need to use the packer scp subcommand, which copies files from a running instance of a Packer image to your local machine2.

B) Execute commands within a running instance of a Packer image. This is not the purpose of the packer inspect subcommand. To execute commands within a running instance of a Packer image, you need to use the packer ssh subcommand, which connects to a running instance of a Packer image via SSH and runs the specified command2.

C) List the artifacts created during the build process of a Packer image. This is not the purpose of the packer inspect subcommand. To list the artifacts created during the build process of a Packer image, you need to use the packer build subcommand with the -machine-readable flag, which outputs the build information in a machine-friendly format that includes the artifact details2.

D) Show usage statistics of a Packer image. This is not the purpose of the packer inspect subcommand. To show usage statistics of a Packer image, you need to use the packer console subcommand with the -stat flag, which launches an interactive console that allows you to inspect and modify variables, sources, and functions, and displays the usage statistics of the current session2. References: 1: packer inspect - Commands | Packer | HashiCorp Developer 2: Commands | Packer | HashiCorp Developer

The FROM statement in a Dockerfile specifies the base image from which the subsequent instructions are executed1. The value of the FROM statement can be either an image name, an image name with a tag, or an image ID1. The image name can be either a repository name or a repository name with a registry prefix2. For example, ubuntu is a repository name, and docker.io/ubuntu is a repository name with a registry prefix2. The tag is an optional identifier that can be used to specify a particular version or variant of an image1. For example, ubuntu:focal refers to the image with the focal tag in the ubuntu repository2. The image ID is a unique identifier that is automatically generated when an image is built or pulled1. For example, sha256:9b0dafaadb1cd1d14e4db51bd0f4c0d56b6b551b2982b2b7c637ca143ad605d2 is an image ID3.

Therefore, the only valid value in the FROM statement among the given options is ubuntu:focal, which is an image name with a tag. The other options are invalid because:

docker://ubuntu:focal is not a valid image name format. The docker:// prefix is used to specify a transport protocol, not a registry prefix4.

registry:ubuntu:focal is not a valid image name format. The registry prefix should be a valid hostname or IP address, not a generic term2.

file:/tmp/ubuntu/Dockerfile is not a valid image name format. The file: prefix is used to specify a local file path, not an image name5.

http://docker.example.com/images/ubuntu-focal.iso is not a valid image name format.  The http:// prefix is used to specify a web URL, not an image name 5.

References:

1: Dockerfile reference | Docker Docs

2: docker - Using FROM statement in dockerfile - Stack Overflow

3: How to get the image id from a docker image - Stack Overflow

4: skopeo - Docker Registry v2 API tool - Linux Man Pages (1)

5: How to build a Docker image from a local Dockerfile? - Stack Overflow

Cloud-init is a tool that allows users to customize the configuration and behavior of cloud instances during the boot process. Cloud-init can process different kinds of data that are passed to the instance via user-data, which is a mechanism provided by various cloud providers to inject data into the instance. Among the kinds of data that cloud-init can process directly from user-data are:

Shell scripts to execute: Cloud-init can execute user-data that is formatted as a shell script, starting with the #!/bin/sh or #!/bin/bash shebang. The script can contain any commands that are valid in the shell environment of the instance. The script is executed as the root user during the boot process12.

Lists of URLs to import: Cloud-init can import user-data that is formatted as a list of URLs, separated by newlines. The URLs can point to any valid data source that cloud-init supports, such as shell scripts, cloud-config files, or include files. The URLs are fetched and processed by cloud-init in the order they appear in the list13.

cloud-config declarations in YAML: Cloud-init can process user-data that is formatted as a cloud-config file, which is a YAML document that contains declarations for various cloud-init modules. The cloud-config file can specify various aspects of the instance configuration, such as hostname, users, packages, commands, services, and more. The cloud-config file must start with the #cloud-config header14.

The other kinds of data listed in the question are not directly processed by cloud-init from user-data. They are either not supported, not recommended, or require additional steps to be processed. These kinds of data are:

ISO images to boot from: Cloud-init does not support booting from ISO images that are passed as user-data. ISO images are typically used to install an operating system on a physical or virtual machine, not to customize an existing cloud instance. To boot from an ISO image, the user would need to attach it as a secondary disk to the instance and configure the boot order accordingly5.

Base64-encoded binary files to execute: Cloud-init does not recommend passing binary files as user-data, as they may not be compatible with the instance’s architecture or operating system. Base64-encoding does not change this fact, as it only converts the binary data into ASCII characters. To execute a binary file, the user would need to decode it and make it executable on the instance6.

References:

User-Data Formats — cloud-init 22.1 documentation

User-Data Scripts

Include File

Cloud Config

How to Boot From ISO Image File Directly in Windows

How to run a binary file as a command in the terminal?.

 Packer is a tool that automates the creation of identical machine images for multiple platforms from a single source configuration. Packer works by creating an instance based on a source image, which is a pre-existing image that serves as a starting point. Packer then connects to the instance through a network connection, such as SSH or WinRM, and runs various commands and scripts to install and configure software within the instance. Packer then shuts down the instance and creates a new system image from it, which can be used to launch new instances. Packer supports many platforms, such as AWS, Azure, VMware, Docker, and others. Packer does not install any software or run any daemon within the target image, nor does it periodically connect to the running instances to re-apply the template. Packer also does not modify the source image directly, but creates a new image from the modified instance. References:

Packer by HashiCorp

HashiCorp Packer - Build Automated Machine Images

Introduction | Packer | HashiCorp Developer

The virt-diff command-line tool can be used to list the differences between files in two virtual machines or disk images. The output shows the changes to a virtual machine’s disk images after it has been running. The command can also be used to show the difference between overlays1. To specify two guests, you have to use the -a or -d option for the first guest, and the -A or -D option for the second guest. For example: virt-diff -a old.img -A new.img1. Therefore, the correct command to list all differences between the disk images vm1-snap.img and vm1.img is: virt-diff -a vm1-snap.img -A vm1.img. The other commands are not related to finding differences between disk images. virt-delta is a tool to create delta disks from two disk images2. virt-cp-in is a tool to copy files and directories into a virtual machine disk image3. virt-cmp is a tool to compare two files or directories in a virtual machine disk image4. virt-history is a tool to show the history of a virtual machine disk image5. References:

21.13. virt-diff: Listing the Differences between Virtual Machine Files …

21.14. virt-delta: Creating Delta Disks from Two Disk Images …

21.6. virt-cp-in: Copying Files and Directories into a Virtual Machine Disk Image …

21.7. virt-cmp: Comparing Two Files or Directories in a Virtual Machine Disk Image …

21.8. virt-history: Showing the History of a Virtual Machine Disk Image …

 Nested page table extensions, such as Intel Extended Page Table (EPT) or AMD Rapid Virtualization Indexing (RVI), are hardware features that facilitate the virtualization of memory. They allow the CPU to perform the translation of guest virtual addresses to host physical addresses in a single step, without the need for software-managed shadow page tables. This reduces the overhead and complexity of memory management for virtual machines, and improves their performance and isolation. Nested page table extensions do not directly affect the virtualization of other hardware components, such as network interfaces, host bus adapters, hard disks, or IO cache.

References:

Second Level Address Translation - Wikipedia

c - What is use of extended page table? - Stack Overflow

Hypervisor From Scratch – Part 4: Address Translation Using Extended …

The command that deletes all volumes which are not associated with a container is docker volume prune. This command removes all unused local volumes, which are those that are not referenced by any containers. By default, it only removes anonymous volumes, which are those that are not given a specific name when they are created. To remove both unused anonymous and named volumes, the --all or -a flag can be added to the command. The command will prompt for confirmation before deleting the volumes, unless the --force or -f flag is used to bypass the prompt. The command will also show the total reclaimed space after deleting the volumes12.

The other commands listed in the question are not valid or do not have the same functionality as docker volume prune. They are either made up, misspelled, or have a different purpose. These commands are:

docker volume cleanup: This command does not exist in Docker. There is no cleanup subcommand for docker volume.

docker volume orphan -d: This command does not exist in Docker. There is no orphan subcommand for docker volume, and the -d flag is not a valid option for any docker volume command.

docker volume vacuum: This command does not exist in Docker. There is no vacuum subcommand for docker volume.

docker volume garbage-collect: This command does not exist in Docker. There is no garbage-collect subcommand for docker volume.

References:

docker volume prune | Docker Docs

How to Remove all Docker Volumes - YallaLabs.

The CPU flag that indicates the hardware virtualization capability on an AMD CPU is SVM. SVM stands for Secure Virtual Machine, and it is a feature of AMD processors that enables the CPU to run virtual machines with hardware assistance. SVM is also known as AMD-V, which is AMD’s brand name for its virtualization technology. SVM allows the CPU to support a hypervisor, which is a software layer that creates and manages virtual machines. A hypervisor can run multiple virtual machines on a single physical machine, each with its own operating system and applications. SVM improves the performance and security of virtual machines by allowing the CPU to directly execute privileged instructions and handle memory access, instead of relying on software emulation or binary translation. SVM also provides nested virtualization, which is the ability to run avirtual machine inside another virtual machine. To use SVM, the CPU must support it and the BIOS must enable it. The user can check if the CPU supports SVM by looking for the svm flag in the /proc/cpuinfo file or by using the lscpu command. The user can also use the virt-host-validate command to verify if the CPU and the BIOS are properly configured for hardware virtualization123. References:

How to check if CPU supports hardware virtualization (VT technology)1

Processor support - KVM3

How to Enable Virtualization in BIOS for Intel and AMD4

The purpose of a .dockerignore file is to specify files that Docker does not submit to the Docker daemon when building a Docker image. A .dockerignore file is a text file that contains a list of files or directories that should be excluded from the build context, which is the set of files and folders that are available for use in a Dockerfile. By using a .dockerignore file, you can avoid sending files or directories that are large, contain sensitive information, or are irrelevant to the Docker image to the daemon, which can improve the efficiency and security of the build process. The other options are incorrect because they do not describe the function of a .dockerignore file. Option A is wrong because a .dockerignore file does not affect the files existing in a Docker image, but only the files sent to the daemon during the build. Option C is wrong because a .dockerignore file does not exist in the root file system of containers, but in the same directory as the Dockerfile. Option D is wrong because a .dockerignore file does not affect the volumes that Docker attaches to a container, but only the files included in the build context. Option E is wrong because a .dockerignore file does not affect the parts of a Dockerfile that are executed, but only the files available for use in a Dockerfile. References:

What are .dockerignore files, and why you should use them?

Dockerfile reference | Docker Docs

How to use .dockerignore and its importance - Shisho Cloud

The default path to the Docker daemon configuration file on Linux is /etc/docker/daemon.json. This file is a JSON file that contains the settings and options for the Docker daemon, which is the service that runs on the host operating system and manages the containers, images, networks, and other Docker resources. The /etc/docker/daemon.json file does not exist by default, but it can be created by the user to customize the Docker daemon behavior. The file can also be specified by using the --config-file flag when starting the Docker daemon. The file must be a valid JSON object and follow the syntax and structure of the dockerd reference docs12. References:

Docker daemon configuration file - Medium3

Docker daemon configuration overview | Docker Docs4

docker daemon | Docker Docs5

Sysprep is a tool that removes all your personal account and security information, and then prepares the machine to be used as an image. It is supported by Windows and some Linux distributions. It can also remove drivers and other machine-specific settings. Sysprep is required when creating a managed image outside of a gallery in Azure

https://learn.microsoft.com/en-us/azure/virtual-machines/generalize

The correct command to boot a QEMU virtual machine using hardware virtualization extensions is qemu -accel kvm -drive file-debian.img -cdrom debian.iso -m 1024 -boot d. This command uses the -accel option to specify the hardware accelerator to use, which in this case is kvm. KVM is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V)1. The -drive option specifies the disk image file to use, which in this case is debian.img. The -cdrom option specifies the ISO image file to use as a CD-ROM, which in this case is debian.iso. The -m option specifies the amount of memory to allocate to the virtualmachine, which in this case is 1024 MB. The -boot option specifies the boot order, which in this case is d, meaning to boot from the CD-ROM first. References:

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_deployment_and_administration_guide/sect-troubleshooting-enabling_intel_vt_x_and_amd_v_virtualization_hardware_extensions_in_bios

https://fedoraproject.org/wiki/Virtualization