305-300 Practice Questions 1 — 50 Questions

Question 1

Which component is responsible for the actual hardware-assisted virtualization in KVM?

Accepted Answer

KVM kernel module. The KVM kernel module (kvm.ko and hardware-specific modules like kvm_intel or kvm_amd) is responsible for hardware-assisted virtualization. It leverages CPU virtualization extensions (Intel VT-x or AMD-V) to execute guest code directly on the host CPU while trapping privileged instructions. This provides near-native performance for virtual machines.

Answer

Virt-manager GUI

Answer

Libvirtd daemon

Answer

QEMU user-mode binary

Question 2

You are managing an LXC container and need to create a snapshot of the container's root file system. Which command achieves this?

Accepted Answer

lxc-snapshot -n container_name. The `lxc-snapshot -n <container_name>` command creates a snapshot of an LXC container's root filesystem. It is the standard LXC utility for snapshotting containers, allowing you to capture the current state of the container's filesystem for backup or rollback purposes.

Answer

lxc-checkpoint -n container_name

Answer

lxc-copy -s container_name

Answer

lxc-backup

Answer

lxc-clone --snapshot

Question 3

In a Packer build process for OpenStack, which 'post-processor' type is typically used to upload the resulting image to the Glance image service?

Accepted Answer

openstack. Packer's `openstack` post-processor takes the artifact produced by the builder (typically a qcow2 or raw image) and uploads it to the OpenStack Glance image service, registering it as a bootable image. It handles authentication against Keystone and can set image metadata such as name, visibility, and tags. This makes it the standard way to publish a Packer-built image into an OpenStack cloud.

Answer

manifest

Answer

shell-local

Answer

compress

Question 4

Which of these is a valid virtualization storage pool type supported by libvirt?

Accepted Answer

dir. libvirt supports several storage pool types, including 'dir' (directory), 'disk', 'fs', 'logical', 'netfs', 'iscsi', 'scsi', 'mpath', 'rbd', 'sheepdog', and 'gluster'. The 'dir' type is a directory-based storage pool that uses a local directory to store volume files. Options like 'cpu', 'interface', and 'network' are not storage pool types; they are related to other libvirt objects such as CPU models, network interfaces, and virtual networks.

Answer

cpu

Answer

interface

Answer

network

Question 5

Which Docker network driver should you use if you want containers to have their own IP addresses on the physical network, as if they were physically connected to the network?

Accepted Answer

macvlan. The macvlan driver assigns each container a unique MAC address and IP address on the physical network, making containers appear as physical devices to the network. This is exactly the behavior described — containers get their own IPs on the physical network.

Answer

bridge

Answer

overlay

Answer

ipvlan

Question 6

In systemd-nspawn, how do you specify a different root directory for the container?

Accepted Answer

-D. The -D flag (long form --directory) in systemd-nspawn specifies the root directory for the container. This is the documented option for pointing nspawn at a directory tree that should be used as the container's filesystem root. For example, 'systemd-nspawn -D /var/lib/machines/mycontainer' boots the container using that path as its root.

Answer

--path

Answer

--root

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-r

Question 7

You need to inspect the metadata of a specific Docker image without pulling it from a remote registry. Which command should you use?

Accepted Answer

docker manifest inspect. 'docker manifest inspect' queries the registry's manifest API directly and returns metadata such as platform variants, digests, and layer information without downloading the image layers. It is the correct tool for inspecting a remote image's metadata without pulling it.

Answer

docker pull --metadata

Answer

docker image history

Answer

docker image inspect

Question 8

In a Vagrantfile, which method is used to pass environment variables into the guest virtual machine during the provisioning phase?

Accepted Answer

config.vm.provision "shell", env: { "VAR" => "value" }. In a Vagrantfile, environment variables are passed to a shell provisioner using the `env` option on the provisioner block: `config.vm.provision "shell", env: { "VAR" => "value" }`. This injects the variables into the environment of the provisioning script running inside the guest. It is the documented, supported way to make host-side values available to guest provisioning.

Answer

config.env.set

Answer

config.vm.env

Answer

vagrant.env.set

Question 9

Which THREE of the following are necessary components for a successful KVM virtualization environment on Linux?

Accepted Answer

The kvm kernel module. Option A (the kvm kernel module) is correct because KVM is implemented as a Linux kernel module that exposes the /dev/kvm interface and provides the core virtualization capability, so without loading kvm (or kvm_intel/kvm_amd) no guest can execute. Option B (QEMU userspace tools) is correct because KVM only handles CPU and memory virtualization in the kernel; QEMU provides the userspace device emulation, BIOS/firmware, and the qemu-system-x86_64 process that actually creates and runs the VM. Option C (hardware support for Intel VT-x or AMD-V) is correct because KVM requires CPU virtualization extensions (vmx or svm) exposed in the CPU flags; without them KVM cannot run hardware-accelerated guests. Option D (a dedicated storage network switch) is not required, since KVM guests can use local disks, files, or any existing network via virtio, and a separate storage switch is only an optional design choice. Option E (a full Xen hypervisor installed) is not required and is in fact an alternative hypervisor; KVM does not depend on Xen, and installing Xen would be a different virtualization stack.

Answer

A dedicated storage network switch

Answer

A full Xen hypervisor installed

Question 10

How do you view the logs of a running container?

Accepted Answer

docker logs [container]. The correct command to view the logs of a running container is `docker logs [container]`. This command retrieves the standard output (stdout) and standard error (stderr) from the container's main process, which Docker captures and stores using a logging driver (default is json-file). It works for both running and stopped containers, and options like `-f` (follow) and `--tail` allow real-time monitoring or limiting output.

Answer

docker show-logs

Answer

cat /var/lib/docker/logs

Answer

docker log

Question 11

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 12

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 13

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

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docker attach

Answer

docker run

Question 14

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 15

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 16

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 17

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 18

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 19

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 20

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