305-300 Practice Test 16 — 15 Questions

Question 1

You need to ensure that a specific package is installed during the first boot of a cloud instance. Which cloud-init key should be added to the configuration?

Accepted Answer

packages. The cloud-init configuration key `packages` is the standard directive for specifying a list of packages to install during instance initialization. It is processed by the `package-update-upgrade-install` module, which runs early in the boot sequence, ensuring the packages are present before other configuration steps. This key works across distributions by using the native package manager (apt, yum, dnf, etc.) to install the listed packages.

Answer

yum_install

Answer

software

Answer

install_packages

Question 2

Which command is used to display the configuration of a Packer build in a readable format?

Accepted Answer

packer inspect. `packer inspect` is the dedicated Packer CLI subcommand that parses a template (HCL2 or legacy JSON) and prints its declared components — builders, provisioners, post-processors, and variables — in a human-readable summary without executing a build. It is the canonical way to review what a template will do before running `packer build`.

Answer

packer view

Answer

packer show

Answer

packer list

Question 3

What is the primary function of a Docker Registry?

Accepted Answer

To store and distribute images. A Docker Registry is a stateless, server-side application that stores and distributes Docker images, acting as the central repository for pushing and pulling image layers. Tools like `docker push` and `docker pull` communicate with the registry's HTTP API (typically on port 5000 or 443) to upload or retrieve images. Docker Hub, Amazon ECR, and Harbor are all examples of registries.

Answer

To build images

Answer

To run containers

Answer

To manage networking

Question 4

When defining a Vagrant network configuration for a libvirt provider, which mode allows the VM to receive an IP address directly from the physical network's DHCP server?

Accepted Answer

public_network. In Vagrant with the libvirt provider, the 'public_network' mode bridges the VM's network interface to a physical network, allowing it to obtain an IP address from the physical network's DHCP server. This makes the VM appear as a separate device on the LAN.

Answer

nat

Answer

forwarded_port

Answer

private_network

Question 5

Which file in a Vagrant project directory is processed by default to define the virtual environment configuration?

Accepted Answer

Vagrantfile. Vagrant automatically reads a file named 'Vagrantfile' in the project directory to determine the configuration of the virtual environment, including the box to use, network settings, provisioning scripts, and provider configuration. This file is written in Ruby DSL syntax and is the single source of truth for a Vagrant project. Without a Vagrantfile, the 'vagrant up' command cannot determine what VM to create.

Answer

settings.json

Answer

provision.sh

Answer

config.yml

Question 6

When using Docker volumes, which type of mount should you use if you want the data to persist on the host filesystem at a specific, user-defined path?

Accepted Answer

Bind mount. A bind mount maps a specific host directory or file path directly into the container, giving the user full control over the exact host location where data persists. This is the correct choice when the requirement is a user-defined, specific host path, because named and anonymous volumes are managed by Docker in its own storage area (/var/lib/docker/volumes) and do not let you choose an arbitrary host path. Bind mounts are the only Docker volume type that satisfies the 'specific, user-defined path' requirement.

Answer

Named volume

Answer

Anonymous volume

Answer

Tmpfs mount

Question 7

You are troubleshooting a container networking issue. You notice that traffic from the container is not being SNATed. What should you check in the iptables rules?

Accepted Answer

nat table, POSTROUTING chain. SNAT (Source NAT) is performed in the nat table's POSTROUTING chain, which is traversed after the routing decision and just before the packet leaves the interface. If container traffic is not being SNATed, the POSTROUTING chain in the nat table is where the MASQUERADE or SNAT rule should exist. Checking this chain will reveal whether the rule is missing, misordered, or not matching the container's source subnet.

Answer

nat table, PREROUTING chain

Answer

filter table, FORWARD chain

Answer

mangle table, OUTPUT chain

Question 8

Which command is used to remove an unused Docker image?

Accepted Answer

docker rmi. The docker rmi command removes one or more Docker images from the local image store. 'rmi' stands for 'remove image' and accepts image names or IDs. This is the direct counterpart to docker rm, which removes containers.

Answer

docker rm

Answer

docker image delete

Answer

docker prune image

Question 9

What is the main advantage of using a container over a virtual machine?

Accepted Answer

Lighter weight and faster startup. Containers share the host OS kernel and only package the application and its dependencies, so they avoid the overhead of booting a full guest OS. This makes them significantly lighter in resource usage and faster to start (often milliseconds to seconds) compared to virtual machines, which must boot an entire OS per instance.

Answer

Ability to run different kernels

Answer

Stronger security isolation

Answer

No network configuration

Question 10

Which THREE of the following attributes can be defined within the <memoryBacking> XML block?

Accepted Answer

. In libvirt domain XML, the element controls how a guest's memory is backed, and it accepts the , , and sub-elements. Option A, , is correct because it instructs libvirt to back the guest RAM with huge pages (e.g., via the hugepages mount) instead of regular 4 KiB pages. Option B, , is correct because it specifies a file-backed memory source (used with shared memory such as a memory-backend-file), which is valid inside . Option E, , is correct because it sets the VFIO/MLOCK-style locking of guest memory in RAM, preventing it from being swapped out. Options C () and D () are not valid children; swap limits and ballooning rates are configured through other mechanisms (e.g., memtune or the device), so they do not belong here.

Answer

<swap-limit/>

Answer

<balloon-rate/>

Question 11

Which THREE storage drivers are supported by Docker?

Accepted Answer

devicemapper. Docker supports the devicemapper storage driver (A), which uses the Device Mapper kernel framework and thin provisioning to manage image and container layers on block devices. It also supports aufs (C), the original copy-on-write union filesystem driver used on older Ubuntu/Debian kernels. The overlay2 driver (E) is the modern, preferred Docker storage driver, using the OverlayFS union filesystem with multiple lower layers for better performance and inode efficiency. Options B (xfs) and D (ext4) are not storage drivers but rather filesystem types; they can serve as the backing filesystem for drivers like overlay2 or devicemapper, but Docker does not use them as storage drivers themselves.

Answer

xfs

Answer

ext4

Question 12

You are troubleshooting a libvirt migration that fails with 'Operation not supported: Migration requires a storage pool'. You need to perform a block migration where the storage is copied to the destination host. Which command-line flag enables this functionality?

Accepted Answer

--copy-storage-all. The --copy-storage-all flag tells libvirt to copy all disk images from the source host to the destination during migration, enabling block migration when shared storage is not available. This directly addresses the 'Migration requires a storage pool' error by supplying the missing storage transfer behavior.

Answer

--live-disk

Answer

--migrate-storage

Answer

--block-migrate

Question 13

Which QEMU-KVM feature allows you to save the state of a VM to a file and resume it later?

Accepted Answer

virsh save. The 'virsh save' command writes the complete state of a running domain (VM) — including CPU registers, memory contents, and device state — to a file, allowing it to be restored later with 'virsh restore'. This is a full VM state save, not just a disk snapshot. It is the libvirt equivalent of hibernation for a virtual machine.

Answer

virsh snapshot

Answer

virsh checkpoint

Answer

virsh suspend

Question 14

You need to enable hugepages for a VM in libvirt to improve memory performance. What XML entry do you add?

Accepted Answer

. To enable hugepages for a libvirt VM, you add a memoryBacking element containing a hugepages child element inside the domain's XML. This tells libvirt/QEMU to back the guest's memory with host hugepages rather than standard 4KB pages. The other XML snippets are not valid libvirt schema.

Answer

<system-memory hugepages='true'/>

Answer

Answer

Question 15

When cleaning up Docker resources, which command will remove all stopped containers, unused networks, and dangling images in one step?

Accepted Answer

docker system prune. docker system prune removes all stopped containers, unused networks, dangling images, and (with -a) unused images in a single command. It is the one-step cleanup command that consolidates what would otherwise require separate container prune, network prune, and image prune invocations.

Answer

docker container prune

Answer

docker volume prune

Answer

docker image prune -a

Answer

docker cleanup