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

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 …

The lxc-attach command allows the user to start a new process within a running LXC container12. It takes the name of the container as an argument and optionally a command to execute inside the container. If no command is specified, it creates a new shell inside the container1. For example, to list all the files in the home directory of a container named myContainer, one can use:

lxc-attach -n myContainer – ls -lh /home

References:

• 1: Executing a command inside a running LXC - Unix & Linux Stack Exchange

 The command virsh list is used to list all running domains (VMs) on the current host. The command virsh list --all can be used to list both active and inactive domains. The other options are not valid virsh commands. The command virsh list is a basic command that lists all running domains (VMs). You can also list all configured VMs by adding the --all option. This is useful if you want to see all VMs configured in the target hypervisor that you can use on subsequent commands1. References:

• 1: 8 Linux virsh subcommands for managing VMs on the command line | Enable Sysadmin.

• 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:

The firmware attribute of the element in a libvirt domain definition specifies the type of firmware used to boot the virtual machine. The valid values for this attribute are efi and bios, which correspond to the Extensible Firmware Interface (EFI) and the Basic Input/Output System (BIOS) respectively. EFI is a newer standard that supports more features and security than BIOS, such as Secure Boot and faster boot times. BIOS is an older standard that is widely compatible and supported by most hypervisors and operating systems. The other values, scsi, virtio, and pcie, are not related to firmware, but to different types of devices or drivers that can be used in a virtual machine. References: 1 (search for firmware enum)

 LXC and Docker are both container technologies that use Linux kernel features to create isolated environments for running applications. The main mechanisms that they use are:

• Linux Capabilities: These are a set of privileges that can be assigned to processes to limit their access to certain system resources or operations. For example, a process with the CAP_NET_ADMIN capability can perform network administration tasks, such as creating or deleting network interfaces. Linux capabilities allow containers to run with reduced privileges, enhancing their security and isolation.
• Kernel Namespaces: These are a way of creating separate views of the system resources for different processes. For example, a process in a mount namespace can have a different file system layout than the host or other namespaces. Kernel namespaces allow containers to have their own network interfaces, process IDs, user IDs, and other resources, without interfering with the host or other containers.
• Control Groups: These are a way of grouping processes and applying resource limits and accounting to them. For example, a control group can limit the amount of CPU, memory, disk I/O, or network bandwidth that a process or a group of processes can use. Control groups allow containers to have a fair share of the system resources and prevent them from exhausting the host resources.

POSIX ACLs and file system permissions are not mechanisms used by LXC and Docker to create containers. They are methods of controlling the access to files and directories on a file system, which can be applied to any process, not just containers.

References:

• LXC vs Docker: Which Container Platform Is Right for You?
• LXC vs Docker: Why Docker is Better in 2023 | UpGuard
• What is the Difference Between LXC, LXD and Docker Containers
• lxc - Which container implementation docker is using - Unix & Linux Stack Exchange

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 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 name5.

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?.

VirtualBox is a hosted hypervisor, which means it runs as an application on top of an existing operating system, not as a special kernel that is booted before the first regular operating system starts1. VirtualBox supports a large number of guest operating systems, including Windows, Linux, Solaris, OS/2, and OpenBSD1. VirtualBox does not require dedicated shared storage, as it can store virtual machine disk images locally on block devices of the virtualization host, or on network shares, or on iSCSI targets1. VirtualBox provides both a graphical user interface (GUI) and command line tools (VBoxManage) to administer virtual machines1. VirtualBox is available for Windows, Linux, macOS, and Solaris hosts1, and does not require the source code of the currently running Linux kernel to be available. References:

• Oracle VM VirtualBox: Features Overview

Libvirt uses XML files to store configuration data for objects in the libvirt API, such as domains, networks, storage, etc. This allows for ease of extension in future releases and validation of documents prior to usage. Libvirt does not use any of the other file formats listed in the question. References:

• libvirt: XML Format
• LPIC-3 Virtualization and Containerization: Topic 305.1: Virtualization Concepts and Theory

The option dom0_mem is used to set the initial and maximum memory size of the Domain-0, which is the privileged domain that starts first and manages the unprivileged domains (DomU) in Xen. The option dom0_mem must be specified in the bootloader configuration, such as GRUB or GRUB2, when Xen is booted. This ensures that the Domain-0 kernel can allocate memory for storing memory metadata and network related parameters based on the boot time amount of memory. If the option dom0_mem is not specified in the bootloader configuration, the Domain-0 will use all the available memory on the host system by default, which may cause performance and security issues. References:

• Managing Xen Dom0′s CPU and Memory
• Xen Project Best Practices
• Dom0 Memory — Where It Has Not Gone

 The correct command to move the libvirt domain web1 from the current host system to the host system host2 is virsh migrate web1 qemu+ssh://host2/system. This command uses the virsh migrate command, which initiates the live migration of a domain to another host1. The first argument is the name of the domain to migrate, which in this case is web1. The second argument is the destination URI, which specifies the connection to the remote host and the hypervisor to use2. In this case, the destination URI is qemu+ssh://host2/system, which means to use the QEMU driver and connect to host2 via SSH, and use the system instance of libvirtd3. The other options are incorrect because they either use invalid commands or arguments, such as node-update, pool-add, patch, or cp, or they do not specify the destination URI correctly. References:

https://balamuruhans.github.io/2019/01/09/kvm-migration-with-libvirt.html

http://libvirt.org/migration.html

Docker stack is a command that allows users to deploy and manage a stack of services on a Docker Swarm cluster. A stack is a group of interrelated services that share dependencies and can be orchestrated and scaled together. A stack is typically defined by a Compose file, which is a YAML file that describes the services, networks, volumes, and other resources of the stack. To use docker stack to run a Compose file on a Swarm, the user must first create and initialize a Swarm cluster, which is a group of machines (nodes) that are running the Docker Engine and are joined into a single entity. The Swarm cluster has one or more managers, which are responsible for maintaining the cluster state and orchestrating the services, and one or more workers, which are the nodes that run the services.

When the user runs docker stack deploy with a Compose file, the command parses the file and creates the services as specified. However, docker stack does not build or upload the images referenced in the Compose file to any registry. Instead, it instructs the Swarm nodes to pull the images from a registry, which can be the public Docker Hub or a private registry. The user must ensure that the images are available in the registry before deploying the stack, otherwise the deployment will fail. The user can use docker build and docker push commands to create and upload the images to the registry, or use an automated build service such as Docker Hub or GitHub Actions. The user must also make sure that the image names and tags in the Compose file match the ones in the registry, and that the Swarm nodes have access to the registry if it is private. By pulling the images from a registry, docker stack ensures that the Swarm nodes have the same and latest version of the images, and that the images are distributed across the cluster in an efficient way.

The other options are not correct. Docker stack does not build the images locally or on the Swarm nodes, nor does it copy or transfer the images to the Swarm nodes. Dockerstack also does not pass the images to the Swarm master, as this would create a bottleneck and a single point of failure. Docker stack relies on the registry as the source of truth for the images, and delegates the image pulling to the Swarm nodes. References:

• Deploy a stack to a swarm | Docker Docs1
• docker stack deploy | Docker Docs2
• docker build | Docker Docs3
• docker push | Docker Docs4

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