305-300 Practice Test 2 — 10 Questions

Question 1

Which instruction in a Dockerfile is best suited for installing packages to minimize image size?

Accepted Answer

RUN apt-get update && apt-get install -y package && rm -rf /var/lib/apt/lists/*. The RUN instruction with apt-get update, install, and cleanup in a single layer is best because it prevents the apt package lists from being stored in the final image. By combining update, install, and rm -rf /var/lib/apt/lists/* in one RUN, Docker creates a single layer where the lists are downloaded, used, and then deleted before the layer is committed. This minimizes image size because the intermediate files never persist in any layer. Other options either don't install packages (COPY, CMD) or leave cached lists in the image (RUN without cleanup).

Answer

COPY apt-cache /

Answer

CMD apt-get install package

Answer

RUN apt-get update && apt-get install -y package

Question 2

Which TWO of the following are valid libvirt storage pool lifecycle commands?

Accepted Answer

pool-start. Option B, pool-start, is correct because it is a genuine virsh subcommand that activates a previously defined but inactive storage pool, making its backing storage available for allocation to guests. Option D, pool-destroy, is correct because it is the valid virsh command that stops an active storage pool, tearing down its runtime state without deleting its persistent definition. The other options are not libvirt commands: pool-halt (A) and pool-reboot (C) are not virsh storage pool subcommands at all, and pool-pause (E) does not exist, since libvirt storage pools have no pause state — only active/inactive and defined/undefined states managed via pool-start, pool-destroy, pool-define, and pool-undefine.

Answer

pool-halt

Answer

pool-reboot

Answer

pool-pause

Question 3

Which command allows you to enter an existing running container and execute a new command inside it?

Accepted Answer

docker exec. The `docker exec` command runs a new process inside an already-running container, which is exactly what is needed to enter a container and execute a command such as a shell. For example, `docker exec -it <container> /bin/bash` opens an interactive shell inside the running container without stopping or restarting it. This is the standard, non-disruptive way to access a running container.

Answer

docker commit

Answer

docker attach

Answer

docker run

Question 4

You are troubleshooting a KVM guest that fails to start with the error 'unsupported configuration: CPU mode 'host-passthrough' requires KVM'. Which of the following is the most likely cause?

Accepted Answer

The guest is configured to use a CPU mode that is only supported by the KVM hypervisor, but the hypervisor is not KVM (e.g., QEMU TCG).. The error 'unsupported configuration: CPU mode 'host-passthrough' requires KVM' occurs when the guest is configured with <cpu mode='host-passthrough'/> but libvirt is not using the KVM hypervisor. This can happen if KVM is not enabled on the host, or if the domain XML explicitly sets a different hypervisor type. host-passthrough exposes the host CPU model and features directly to the guest, which is only possible with hardware virtualization.

Answer

The host CPU is too old and does not support the host-passthrough mode.

Answer

The guest's XML configuration has a typo in the CPU mode attribute.

Answer

The host CPU does not support hardware virtualization extensions.

Question 5

What is the purpose of the 'rkt' (Rocket) container runtime?

Accepted Answer

To run pods in a secure, pluggable manner. The 'rkt' (Rocket) container runtime was developed by CoreOS as an alternative to Docker, designed to run application containers (often grouped into pods) with a strong focus on security, composability, and adherence to open standards. It implements a pluggable execution model where different isolation mechanisms (e.g., KVM, cgroups) can be used, and it supports pod-level networking and image formats like ACI (App Container Image). Its primary purpose is to securely and portably run containerized workloads, especially pods, in a pluggable manner.

Answer

To replace the kernel

Answer

To manage cloud infrastructure

Answer

To provide a GUI for Docker

Question 6

Which THREE of the following steps are involved in performing a manual disk migration of a VM?

Accepted Answer

Editing the domain XML on the target host. Manual disk migration of a VM requires copying the VM's disk image to the target host (D), since the storage must be present there before the domain can run; this is typically done with tools like rsync, scp, or cp. The target host's domain XML must then be edited (A) to point to the new disk path and any host-specific settings, because the original XML references the source host's storage location. Finally, the domain is registered on the target host with virsh define (C), which loads the edited XML into libvirt so the VM can be started. Options B and E are not part of the process: reformatting the disk image would destroy the guest's data and filesystem, and updating the host kernel is unrelated to migrating a VM's disk and domain definition.

Answer

Reformatting the disk image

Answer

Updating the host kernel

Question 7

Which command shows the history of layers in a Docker image?

Accepted Answer

docker history. The `docker history` command displays the complete layer history of a Docker image, showing each intermediate layer created by the Dockerfile instructions, along with the layer ID, creation time, size, and the command that created it. This is the standard way to inspect how an image was built and identify which layers consume the most space.

Answer

docker log

Answer

docker layers

Answer

docker image info

Question 8

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

Answer

isolated

Answer

direct

Question 9

You are running a Docker container and need to map port 8080 on the host to port 80 in the container. Which command argument should you use?

Accepted Answer

-p 8080:80. The -p flag (short for --publish) maps a host port to a container port using the format -p HOST_PORT:CONTAINER_PORT. Since the requirement is to expose container port 80 on host port 8080, the correct syntax is -p 8080:80. Docker's port publishing always places the host port on the left of the colon and the container port on the right.

Answer

-p 80:8080

Answer

--port 8080:80

Answer

--map 8080:80

Question 10

When using 'docker-compose', which file format is used to define the services?

Accepted Answer

YAML. Docker Compose uses YAML (Yet Another Markup Language / YAML Ain't Markup Language) files, conventionally named docker-compose.yml or compose.yaml, to define services, networks, volumes, and build contexts. YAML's indentation-based structure maps cleanly to Compose's nested service definitions. INI, XML, and JSON are not supported by Compose for its primary configuration file.

Answer

INI

Answer

XML

Answer

JSON