305-300 Full Virtualization Practice Test 3 — 15 Questions

Question 1

What is the primary function of the libvirtd daemon?

Accepted Answer

To act as a management API for virtualization technologies. The libvirtd daemon is the core management service in the libvirt ecosystem, providing a stable, hypervisor-agnostic API (via C, Python, etc.) that abstracts underlying virtualization technologies like KVM, QEMU, Xen, and LXC. It listens on a Unix socket (and optionally TCP) to accept management commands for creating, starting, stopping, and monitoring virtual machines. Thus, it acts as a management API for virtualization technologies, not as a hardware emulator or kernel module manager.

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To manage kernel modules for KVM

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To emulate physical hardware for the host

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To provide a graphical interface for QEMU

Question 2

You need to convert a raw disk image to QCOW2 format to enable snapshotting. Which command is correct?

Accepted Answer

qemu-img convert -f raw -O qcow2 source.img target.qcow2. The correct syntax is 'qemu-img convert -f raw -O qcow2 source.img target.qcow2'. The -f flag specifies the source format and -O (capital O) specifies the destination format. This is the canonical way to convert a raw image into QCOW2 so that snapshots, compression, and backing files become available.

Answer

qemu-img convert -i raw -o qcow2 source.img target.qcow2

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virsh image-convert source.img target.qcow2

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qemu-img change -f raw -t qcow2 source.img

Question 3

You want to optimize disk I/O performance for a KVM guest. Which bus type should you configure in the libvirt domain XML for the virtual disk?

Accepted Answer

virtio. Virtio is a paravirtualized I/O driver framework designed specifically for KVM guests, providing near-native disk I/O performance by reducing the overhead of full hardware emulation. Configuring the disk bus as virtio in the libvirt domain XML (using <target dev='vda' bus='virtio'/>) allows the guest to use the virtio-blk or virtio-scsi driver, which significantly outperforms emulated IDE or SCSI controllers. This is the recommended bus type for production KVM workloads.

Answer

scsi

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usb

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ide

Question 4

In a Xen environment, which command would you use to change the number of VCPUs allocated to a running domain 'dom1' to 4?

Accepted Answer

xl vcpu-set dom1 4. In a Xen environment managed via the xl toolstack (the modern replacement for xm), the xl vcpu-set command is used to change the number of virtual CPUs assigned to a running domain. The syntax 'xl vcpu-set dom1 4' sets domain dom1 to 4 VCPUs. This is the Xen-native equivalent of virsh setvcpus in libvirt-managed environments.

Answer

virsh setvcpus dom1 4

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xl mem-set dom1 4

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xm set-vcpu dom1 4

Question 5

You are using libvirt to manage a QEMU VM. You want to pass a specific host USB device with vendor ID 1234 and product ID 5678 to the guest. Which XML element is used inside the <devices> block to define this?

Accepted Answer

. Libvirt's canonical way to pass a host USB device to a guest is the element with mode='subsystem' and type='usb', containing a block with and . This tells QEMU to detach the device from the host and attach it to the guest via USB redirection, and the IDs must be in hexadecimal with the 0x prefix.

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Answer

Answer

<usb-passthrough vendor='1234' product='5678'/>

Question 6

Which libvirt network type uses a bridge on the host to connect virtual machines directly to the physical network?

Accepted Answer

bridge. A libvirt network of type 'bridge' uses an existing host bridge (e.g., br0) to connect guest interfaces directly to the physical LAN. The guests obtain IPs from the same DHCP server as the host and appear as peers on the physical network. This is the standard way to give VMs routable, first-class network presence.

Answer

nat

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isolated

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direct

Question 7

In the context of virtualization, what does 'ballooning' refer to?

Accepted Answer

Dynamically resizing guest memory. Ballooning is a memory reclamation technique where a special 'balloon' driver inside the guest OS inflates by allocating guest memory pages, forcing the guest to swap or release them back to the hypervisor for use by other VMs. When the hypervisor needs memory, it tells the balloon to inflate; when memory pressure subsides, the balloon deflates and returns pages to the guest. This allows dynamic resizing of guest memory without rebooting the VM.

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Scaling network bandwidth for a VM

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Increasing the number of virtual CPUs

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Compressing disk images on the fly

Question 8

A VM is hanging because of a specific hardware emulation bug in QEMU. You need to enable the 'qxl' video device to see if it resolves display issues. What is the XML tag to define the video device in the domain config?

Accepted Answer

. In libvirt domain XML, video devices are defined with the

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Answer

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Question 9

Which file system format is specifically designed for QEMU/KVM to support advanced features like copy-on-write, snapshots, and compression?

Accepted Answer

qcow2. qcow2 (QEMU Copy-On-Write version 2) is the native QEMU/KVM disk image format designed to support copy-on-write, internal and external snapshots, zlib/zstd compression, and encryption. It grows dynamically as data is written and only allocates blocks on demand, making it ideal for VM images where space efficiency and snapshotting matter.

Answer

vmdk

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vhdx

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raw

Question 10

How do you define a new libvirt virtual network from an XML file named 'net.xml'?

Accepted Answer

virsh net-define net.xml. The virsh net-define command parses an XML file and defines a persistent libvirt virtual network from it, registering the network configuration with libvirt without starting it. This is the correct command to load a network definition from net.xml into libvirt's configuration.

Answer

virsh net-load net.xml

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virsh define net.xml

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virsh net-create net.xml

Question 11

Which command is used to display the XML configuration of a running VM domain named 'webserver'?

Accepted Answer

virsh dumpxml webserver. virsh dumpxml outputs the full XML definition of a domain, and when the domain is running it reflects the live configuration. This is the standard libvirt command for inspecting a VM's XML. The other options are not valid virsh subcommands for this purpose.

Answer

virsh export webserver

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virsh show-config webserver

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virsh get-xml webserver

Question 12

You want to limit the bandwidth of a virtual network interface. Which XML element within <interface> allows you to configure this?

Accepted Answer

. The element inside is the libvirt XML mechanism for traffic shaping on a virtual NIC. It contains and child elements, each accepting an 'average' attribute in kilobytes per second, which sets the token-bucket rate limit enforced by the host's traffic control subsystem.

Answer

<limit-rate>1000</limit-rate>

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<network-speed>1000</network-speed>

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<traffic-control>1000</traffic-control>

Question 13

What does the term 'KVM' stand for?

Accepted Answer

Kernel-based Virtual Machine. KVM stands for Kernel-based Virtual Machine. It is a Linux kernel module that turns the Linux kernel into a Type-1 hypervisor by exposing hardware virtualization extensions (Intel VT-x, AMD-V) through /dev/kvm. QEMU typically runs on top of KVM to provide full machine emulation and device models.

Answer

K-Hypervisor Virtual Machine

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Kernel Virtual Module

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Kilo-Virtual Machine

Question 14

You are using QEMU to emulate an ARM architecture on an x86 host. Which binary would you typically use to execute this?

Accepted Answer

qemu-system-arm. qemu-system-arm is the QEMU binary that emulates a full ARM system, including CPU, memory, and peripherals, allowing you to run an ARM operating system on an x86 host. The 'system' prefix indicates full-system emulation, as opposed to user-mode emulation. This is the correct binary for booting an ARM kernel or OS image.

Answer

qemu-x86_64-arm

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qemu-arm

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qemu-system-x86_64

Question 15

You need to attach a new block device to a running VM. What virsh command achieves this?

Accepted Answer

virsh attach-disk vm_name /path/to/img vda. The virsh attach-disk command is the standard way to hot-plug a new block device to a running domain. Its syntax is 'virsh attach-disk ' where source is the host image path and target is the guest device name (e.g., vda, vdb). This command modifies the domain's live XML and, with --persistent, also updates the saved configuration.

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virsh attach-device-file vm_name /path/to/img

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virsh add-device vm_name /path/to/img

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virsh hotplug-disk vm_name /path/to/img