305-300 Practice Test 12 — 15 Questions

Question 1

You are creating a Vagrant environment for a development team. The team needs a single VM that uses the 'ubuntu/jammy64' box and forwards host port 8080 to guest port 80. Which Vagrantfile configuration block correctly defines this?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

config.vm.box = "ubuntu/jammy64"
config.vm.network "forwarded_port", guest: 80, host: 8080. Vagrant port forwarding is configured with config.vm.network "forwarded_port", specifying guest and host ports. The correct option sets the box to ubuntu/jammy64 and maps host port 8080 to guest port 80. Other options define private networks, synced folders, or provisioners, which do not provide the required port forwarding functionality.

Answer

config.vm.box = "ubuntu/jammy64"
config.vm.network "private_network", ip: "192.168.33.10"

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config.vm.box = "ubuntu/jammy64"
config.vm.provision "shell", inline: "apt-get update"

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config.vm.box = "ubuntu/jammy64"
config.vm.synced_folder ".", "/var/www", type: "nfs"

Question 2

You are setting up a KVM guest that requires very low latency for a real-time workload. You want to dedicate a physical CPU core to the guest and prevent the host from scheduling other tasks on that core. Which libvirt domain XML configuration achieves this?

Accepted Answer

combined with host kernel parameters isolcpus=2 and nohz_full=2.. To dedicate and isolate a physical core for a guest, you must both pin the vCPU to that core using vcpupin and configure the host kernel to exclude that core from general scheduling with isolcpus and nohz_full. Pinning alone only restricts where the guest runs; it does not prevent the host from using the core for other tasks. The combination provides the required isolation.

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Answer

Answer

Question 3

You are using Docker and need to view the layers that make up an image to understand its build history. Which command should you use?

Accepted Answer

docker history <image>. The docker history command lists the layers of an image along with the commands that created them, making it the right tool to understand build history. docker inspect provides metadata but not a layer-by-layer history, docker layers does not exist, and docker diff is for container filesystem changes. Therefore, docker history is the correct answer.

Answer

docker inspect <image>

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docker layers <image>

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docker diff <image>

Question 4

You administer a KVM host running libvirt. A developer needs a guest to be able to communicate with the host directly over a private network without any NAT or bridging to the physical LAN. You decide to use libvirt's default virtual network. Which virsh command will display the XML definition of this default network so you can inspect its forwarding mode and DHCP range?

Accepted Answer

virsh net-dumpxml default. The net-dumpxml subcommand is the canonical way to retrieve the XML configuration of a libvirt virtual network. Inspecting the default network's XML reveals its NAT forwarding mode and DHCP range, which is precisely what the scenario requires. Other net-* subcommands either list runtime state or leases rather than the full definition.

Answer

virsh net-dhcp-leases default

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virsh net-list --info default

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virsh iface-dumpxml default

Question 5

You are using Packer to build an image for a private cloud. The build uses the 'qemu' builder and a 'shell' provisioner. The provisioner script runs but fails to install a package because the package repository is unreachable. You suspect the VM has no network connectivity during provisioning. Which Packer feature should you verify to ensure the VM has network access?

Accepted Answer

The 'net_device' setting in the qemu builder configuration.. The qemu builder's 'net_device' setting defines the network interface for the VM. If it is set to 'none' or lacks a proper backend, the VM will have no network connectivity, causing package installations to fail. Packer's default qemu configuration usually includes a user-mode network, but explicit overrides can disable it. Checking this setting ensures the VM can reach external repositories during provisioning.

Answer

The 'accelerator' setting in the qemu builder configuration.

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The 'http_directory' setting in the builder configuration.

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The 'communicator' setting in the builder configuration.

Question 6

You are running a Docker container that needs to persist data in a directory that is backed by a storage area on the host. The host uses the overlay2 storage driver. You want the container to write data that survives container removal and is accessible directly on the host filesystem. Which approach should you use?

Accepted Answer

Use a bind mount to map a host directory into the container.. Bind mounts directly associate a host directory with a container path, so files written by the container are stored on the host and persist after the container is removed. They also allow direct access to the data from the host without Docker-specific commands. Named volumes persist but are managed by Docker, while tmpfs is memory-only and commits are for image creation, not runtime data persistence.

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Commit the container to a new image after writing data, and run a new container from that image.

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Create a named volume with docker volume create and mount it into the container.

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Use a tmpfs mount to store the data in memory.

Question 7

You need to enable and configure a UEFI firmware boot for a new KVM guest on a libvirt host. Which TWO of the following steps are required? (Choose two.)

Accepted Answer

Set the domain's element to use with the OVMF code and variable store paths, or select the UEFI firmware via the firmware autoselection feature.. Enabling UEFI boot requires the OVMF firmware files to be present on the host and the domain XML to reference them via a pflash loader or firmware autoselection. Neither the disk image format nor the guest agent is relevant to UEFI support, and there is no 'uefi' boot device value in libvirt XML.

Answer

Disable the QEMU guest agent channel because it conflicts with UEFI variable services.

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Convert the guest disk image from qcow2 to raw format because UEFI firmware cannot boot from qcow2.

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Add a element to the domain's section to select UEFI boot order.

Question 8

You are configuring cloud-init to inject an SSH key into a new VM. Which directive in the configuration metadata ensures the key is added to the correct user's authorized_keys file?

Accepted Answer

ssh_authorized_keys. In cloud-init user-data, the ssh_authorized_keys directive is a per-user key that specifies which SSH public keys should be written to that user's ~/.ssh/authorized_keys file. It is nested under the users list entry for the target user, ensuring the key lands in the correct account's authorized_keys rather than being applied globally.

Answer

users.ssh_key

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ssh_keys

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authorized_keys_file

Question 9

What is the role of the 'Dockerfile' in the container build process?

Accepted Answer

To provide build instructions. A Dockerfile is a text file containing a series of instructions (FROM, RUN, COPY, CMD, etc.) that Docker uses to build a container image. It defines the base image, dependencies, environment, and startup command, effectively providing the build recipe. The 'docker build' command reads the Dockerfile and executes each instruction in order to produce a layered image.

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To define network topology

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To list running containers

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To store container data

Question 10

In an OpenVZ environment, you need to limit the number of processes a container can create. Which parameter in the container configuration file should be modified?

Accepted Answer

NUMPROC. In OpenVZ, the NUMPROC parameter in the container's configuration file (e.g., /etc/vz/conf/CTID.conf) directly controls the maximum number of processes and threads that can exist within that container. It acts as a hard limit on the total process count, preventing a single container from exhausting the host's process table. This is the correct parameter to modify when you need to restrict process creation for a specific container.

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PHYSPAGES

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KMEMSIZE

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PRIVVMPAGES

Question 11

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 12

You have an active domain named 'myvm'. How do you gracefully shut it down?

Accepted Answer

virsh shutdown myvm. 'virsh shutdown myvm' sends an ACPI shutdown signal to the guest, allowing the guest OS to run its shutdown sequence gracefully. This is the correct way to power off a domain cleanly. It requires the guest to have ACPI support and a running acpid/systemd to honor the request.

Answer

virsh stop myvm

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virsh poweroff myvm

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virsh destroy myvm

Question 13

You are configuring a virtual network with a static IP address for a VM. Where do you define the DHCP host entry in the libvirt network XML?

Accepted Answer

. In libvirt's network XML schema, static DHCP reservations are declared inside the element using a child element, which binds a MAC address to a fixed IP (and optionally a name). The syntax is the canonical form recognized by libvirt's network parser when the network is in 'nat' or 'isolated' forward mode with a DHCP range defined. This ensures dnsmasq hands the same IP to the VM every time it boots.

Answer

<ip-assignment mac='...' ip='...'/>

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<dhcp-host mac='...' ip='...'/>

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<static-ip mac='...' ip='...'/>

Question 14

Which TWO of the following are valid storage pool types in libvirt?

Accepted Answer

logical. Option C (logical) is correct because libvirt defines a 'logical' storage pool type that manages LVM volume groups, allowing volumes to be created as logical volumes within an existing VG. Option E (iscsi) is correct because libvirt supports an 'iscsi' storage pool type that connects to an iSCSI target and exposes its LUNs as volumes via the iscsi-direct or iscsi pool driver. The other options are not valid libvirt pool types: 'nfs-server' is not a pool type (NFS is handled by the 'netfs' pool type), 'virtual-disk' is not a recognized libvirt pool type, and 'remote-disk' is not a libvirt pool type either. Valid libvirt pool types include dir, fs, netfs, logical, disk, iscsi, scsi, mpath, rbd, sheepdog, gluster, zfs, and vstorage, which confirms that only logical and iscsi fit the scenario.

Answer

nfs-server

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virtual-disk

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remote-disk

Question 15

You need to change the MAC address of a network interface for a virtual machine. Where is this configured?

Accepted Answer

Inside the tag of the VM XML. A VM's MAC address is defined in the libvirt domain XML inside the element, typically as within or . Editing this XML and redefining the domain is the standard way to change a VM's MAC address.

Answer

Via the 'virsh set-mac' command

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In the qemu-system-x86_64 startup parameters

Answer

In the host's /etc/network/interfaces