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

The CPU architecture of a QEMU virtual machine is independent of the host system’s architecture. QEMU can emulate many CPU architectures, including x86, ARM, Alpha, and SPARC, regardless of the host system’s architecture1. This allows QEMU to run guest operating systems that are not compatible with the host system’s hardware. Therefore, option A is correct. QEMU virtual machines support multiple virtual CPUs in order to run SMP systems. QEMU uses the concept of virtual CPUs (vCPUs) to map the virtual machines to physical CPUs. Each vCPU is a thread that runs on a physical CPU core. QEMU allows the user to specify the number of vCPUs and the CPU model for each virtual machine. QEMU can run SMP systems with multiple vCPUs, as well as single-processor systems with one vCPU2. Therefore, option E is also correct. The other options are incorrect because they do not describe the CPU of a QEMU virtual machine. Option B is wrong because QEMU virtual machines can have more than one CPU with more than one core. Option C is wrong because QEMU does not require a dedicated physical CPU core for each virtual machine. QEMU can share the physical CPU cores among multiple virtual machines, depending on the load and the scheduling policy. Option D is wrong because QEMU does not use the term CPU, but vCPU, to refer to the virtual machines’ processors. References:

QEMU vs VirtualBox: What’s the difference? - LinuxConfig.org

QEMU / KVM CPU model configuration — QEMU documentation

Introduction — QEMU documentation

Qemu/KVM Virtual Machines - Proxmox Virtual Environment

LXC (Linux Containers) is a lightweight virtualization technology that allows multiple isolated Linux systems (containers) to run on the same host. LXC uses Linux kernel features such as namespaces, cgroups, and AppArmor to create and manage containers. Each container has its own file system, network interfaces, process tree, and resource limits. However, containers share the same kernel and hardware with the host, which makes them more efficient and faster than full virtualization.

By default, an LXC container has a minimal set of devices that are needed for its operation. These devices are created by the LXC library when the container is started, and are removed when the container is stopped. The default devices are:

/dev/log: This is a Unix domain socket that connects to the syslog daemon on the host. It allows the container to send log messages to the host’s system log1.

/dev/console: This is a character device that provides access to the container’s console. It is usually connected to the host’s terminal or a file. It allows the container to interact with the user or the host’s init system12.

/dev/urandom: This is a character device that provides an unlimited source of pseudo-random numbers. It is used by various applications and libraries that need randomness, such as cryptography, UUID generation, and hashing13.

The other devices listed in the question do not exist by default in an LXC container. They are either not needed, not allowed, or not supported by the container’s namespace or cgroup configuration. These devices are:

/dev/kmem: This is a character device that provides access to the kernel’s virtual memory. It is not needed by the container, as it can access its own memory through the /proc filesystem. It isalso not allowed by the container, as it would expose the host’s kernel memory and compromise its security4.

/dev/root: This is a symbolic link that points to the root device of the system. It is not supported by the container, as it does not have a separate root device from the host. The container’s root file system is mounted from a directory, an image file, or a loop device on the host5.

References:

Linux Containers - LXC - Manpages - lxc.container.conf.5

Linux Containers - LXC - Getting started

Random number generation - Wikipedia

/dev/kmem - Wikipedia

Linux Containers - LXC - Manpages - lxc.container.conf.5

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

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

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

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

 cloud-init uses the /var/lib/cloud/ directory to store status information and configuration information retrieved from external sources, such as the cloud platform’smetadata service or user data files. The directory contains subdirectories for different types of data, such as instance, data, handlers, scripts, and sem. The instance subdirectory contains information specific to the current instance, such as the instance ID, the user data, and the cloud-init configuration. The data subdirectory contains information about the data sources that cloud-init detected and used. The handlers subdirectory contains information about the handlers that cloud-init executed. The scripts subdirectory contains scripts that cloud-init runs at different stages of the boot process, such as per-instance, per-boot, per-once, and vendor. The sem subdirectory contains semaphore files that cloud-init uses to track the execution status of different modules and stages. References:

Configuring and managing cloud-init for RHEL 8 - Red Hat Customer Portal

vsphere - what is the linux file location where the cloud-init user …

The ENTRYPOINT instruction in a Dockerfile specifies the default command to run when a container is started from the image. The ENTRYPOINT instruction can be written in two forms: exec form and shell form. The exec form uses a JSON array to specify the command and its arguments, such as [ “executable”, “param1”, “param2” ]. The shell form uses a single string to specify the command and its arguments, such as “executable param1 param2”. The shell form is converted to the exec form by adding /bin/sh -c to the beginning of the command. Therefore, the following statements in a Dockerfile are equivalent and will lead to a container that outputs hello world:

ENTRYPOINT [ “echo hello world” ] ENTRYPOINT [ “/bin/sh”, “-c”, “echo hello world” ] ENTRYPOINT “echo hello world” ENTRYPOINT [ “echo”, “hello”, “world” ] ENTRYPOINT [ “/bin/sh”, “-c”, “echo”, “hello”, “world” ] ENTRYPOINT “echo hello world”

The other statements in the question are invalid or incorrect. The statement A. ENTRYPOINT “echo Hello World” is invalid because it uses double quotes to enclose the entire command, which is not allowed in the shell form. The statement D. ENTRYPOINT echo Hello World is incorrect because it does not use quotes to enclose the command, which is required in the shell form. The statement E. ENTRYPOINT “echo”, “Hello”, “World” is invalid because it uses double quotes to separate the command and its arguments, which is not allowed in the exec form. References:

Dockerfile reference | Docker Docs

Using the Dockerfile ENTRYPOINT and CMD Instructions - ATA Learning

Difference Between run, cmd and entrypoint in a Dockerfile

 LXD supports the following network interface types for containers: macvlan, bridged, physical, sriov, and ovn1. Macvlan creates a virtual interface on the host that is connected to the same network as the parent interface2. Bridged connects the container to a network bridge that acts as a virtual switch3. Physical attaches the container to a physical network interface on the host2. Ipsec and wifi are not valid network interface types for LXD containers. References:

1: Bridge network - Canonical LXD documentation

2: How to create a network - Canonical LXD documentation

4: LXD containers and networking with static IP - Super User

IaaS is a type of cloud computing service that offers essential compute, storage, and networking resources on demand, on a pay-as-you-go basis. IaaS is one of the four types of cloud services, along with software as a service (SaaS), platform as a service (PaaS), and serverless12. IaaS eliminates the need for enterprises to procure, configure, or manage infrastructure themselves, and they only pay for what they use23. Some examples of IaaS providers are Microsoft Azure, Google Cloud, and Amazon Web Services.

Resource management for full virtualization is the process of allocating and controlling the physical resources of the host system to the virtual machines running on it. The hypervisor is the software layer that performs this task, by providing each virtual machine with a virtual hardware of a defined capacity that limits the resources of the virtual machine. For example, the hypervisor can specify how many virtual CPUs, how much memory, and how much disk space each virtual machine can use. The hypervisor can also enforce resource isolation and prioritization among the virtual machines, to ensure that they do not interfere with each other or consume more resources than they are allowed to. The hypervisor cannot provide fine-grained limits to internal elements of the guest operating system, such as the number of processes, because the hypervisor does not have access to the internal state of the guest operating system. The guest operating system is responsible for managing its own resources within the virtual hardware provided by the hypervisor. For example, the guest operating system can create an arbitrary amount of network sockets, as long as it does not exceed the network bandwidth allocated by the hypervisor. Full virtualization can pose limits to virtual machines, and does not always assign the host system’s resources in a first-come-first-serve manner. The hypervisor can use various resource management techniques, such as reservation, limit, share, weight, and quota, to allocate and control the resources of the virtual machines. The hypervisor can also use resource scheduling algorithms, such as round-robin, fair-share, or priority-based, to distribute the resources among the virtual machines according to their needs and preferences. All processes created within the virtual machines are not transparently and equally scheduled in the host system for CPU and I/O usage. The hypervisor can use different scheduling policies, such as proportional-share, co-scheduling, or gang scheduling, to schedule the virtual CPUs of the virtual machines on the physical CPUs of the host system. The hypervisor can alsouse different I/O scheduling algorithms, such as deadline, anticipatory, or completely fair queuing, to schedule the I/O requests of the virtual machines on the physical I/O devices of the host system. The hypervisor can also use different resource accounting and monitoring mechanisms, such as cgroups, perf, or sar, to measure and report the resource consumption and performance of the virtual machines. References:

Oracle VM VirtualBox: Features Overview

Resource Management as an Enabling Technology for Virtualization - Oracle

Introduction to virtualization and resource management in IaaS | Cloud Native Computing Foundation

 The command vagrant init is used to initialize the current directory to be a Vagrant environment by creating an initial Vagrantfile if one does not already exist1. The Vagrantfile contains the configuration settings for the Vagrant box, such as the box name, box URL, network settings, synced folders, provisioners, etc. The command vagrant init does not execute any provisioning tool, start any box, install Vagrant on a Linux host, or download any box. Those actions are performed by other Vagrant commands, such as vagrant provision, vagrant up, vagrant install, and vagrant box add, respectively. References:

1: vagrant init - Command-Line Interface | Vagrant | HashiCorp Developer

The type attribute of a element in a libvirt domain definition specifies the hypervisor used for running the domain. The allowed values are driver specific, but include “xen”, “kvm”, “hvf” (since 8.1.0 and QEMU 2.12), “qemu” and "lxc"1. Therefore, the valid values among the options are C. kvm and E. lxc. KVM stands for Kernel-based Virtual Machine, which is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V)2. LXC stands for Linux Containers, which is an operating system-level virtualization method for running multiple isolated Linux systems (containers) on a single control host3. The other options are not valid values for the type attribute, asthey are either not hypervisors or not supported by libvirt. References:http://libvirt.org/formatdomain.html

https://libvirt.org/formatcaps.html

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

Containerd is an industry-standard container runtime that uses Runc (a low-level container runtime) by default, but can be configured to use others as well1. Containerd manages the complete container lifecycle of its host system, from image transfer and storage to containerexecution and supervision1. It supports the standards established by the Open Container Initiative (OCI)1. Containerd does not require the Docker engine and Docker CLI to be installed, as it can be used independently or with other container platforms2. Containerd is not a text file format, nor does it run in each Docker container or provide DHCP client functionality. Containerd is not the initial process run at the start of any Docker container, as that is the role of the container runtime, such as Runc3. References: 1 (search for “containerd”), 2 (search for “Containerd is an open source”), 3 (search for “It uses rune to start containers”).