305-300 Practice Test 5 — 10 Questions

Question 1

Which TWO of the following commands are used for VM disk image management?

Accepted Answer

qemu-img create. Option B, `qemu-img create`, is correct because it is the standard qemu-img subcommand used to create a new VM disk image, specifying the format (e.g., qcow2, raw) and size. Option E, `qemu-img info`, is correct because it displays metadata about an existing disk image, such as its virtual size, disk size, format, and backing file. The other options are not valid qemu-img subcommands: `qemu-img list` (A) does not exist for enumerating images, `qemu-img status` (C) is not a qemu-img operation, and `qemu-img format` (D) is not a subcommand — formatting is done via the `-f`/`-O` options on create/convert.

Answer

qemu-img list

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qemu-img status

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qemu-img format

Question 2

What is the primary function of the cloud-init 'runcmd' module?

Accepted Answer

Running arbitrary shell commands. The cloud-init `runcmd` module executes arbitrary shell commands on the instance during the final stage of boot, after other configuration modules have run. It is commonly used to run scripts, start services, or perform custom setup that is not covered by declarative modules. Because it runs late in the boot sequence, it can rely on packages and files configured by earlier modules.

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Setting the system locale

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Configuring users

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Installing software packages

Question 3

You are troubleshooting a Docker container that cannot reach the internet despite the host having connectivity. The container uses the default bridge network. Which iptables chain is most likely causing the block?

Accepted Answer

FORWARD. Docker's default bridge network relies on the host's FORWARD chain to route packets between the docker0 bridge and the external interface. If the FORWARD chain's default policy is DROP (common on hardened hosts or when firewalld/ufw is misconfigured), container traffic is silently dropped even though the host itself has internet access. Docker normally inserts its own DOCKER-USER and DOCKER-FORWARD rules to permit this, but a conflicting firewall rule or a policy change can override them.

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PREROUTING

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POSTROUTING

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OUTPUT

Question 4

What is the purpose of the 'ENTRYPOINT' instruction in a Dockerfile?

Accepted Answer

To configure the container as an executable. ENTRYPOINT configures the container to run as an executable by defining the command that executes when the container starts. Arguments passed on 'docker run' are appended to ENTRYPOINT rather than replacing it, which is what makes the container behave like a standalone binary. This is distinct from CMD, which provides overridable defaults.

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To run build-time commands

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To copy files

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To set environment variables

Question 5

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

Question 6

Which command is used to start a VM that has been defined?

Accepted Answer

virsh start vm_name. The correct command to start a defined but inactive libvirt domain (VM) is `virsh start vm_name`. This command initiates the domain from its persistent XML definition, transitioning it from the 'shut off' state to 'running'. It is the standard counterpart to `virsh shutdown` and `virsh destroy`.

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virsh launch vm_name

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virsh boot vm_name

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virsh run vm_name

Question 7

You are configuring a virtual network in libvirt that allows VMs to communicate with each other and the host, but prevents them from accessing the external network. Which mode should you select for this network?

Accepted Answer

Isolated. An isolated libvirt network allows VMs to communicate with each other and with the host but provides no route to the external network, which is exactly the requirement. It uses a virtual bridge with no forwarding to a physical interface or NAT. The other modes all provide some form of external connectivity.

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Bridge

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Direct

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NAT

Question 8

You are using QEMU to emulate an ARM architecture on an x86_64 host. You need to ensure the guest has access to the host's filesystem directly without configuring network shares. Which option is the correct way to pass a directory through to the guest?

Accepted Answer

-virtfs local,path=/data,mount_tag=host_data,security_model=passthrough. The -virtfs option with local,path=/data,mount_tag=host_data,security_model=passthrough configures a virtio-9p filesystem share that allows the guest to mount the host directory directly. This is the correct QEMU mechanism for passing a host directory to the guest without network shares.

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-fsdev share,path=/data,id=host_data

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-netdev user,hostfwd=dir:/data

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-drive file=/data,format=raw,if=virtio

Question 9

Which THREE directives are valid under the cloud-init 'users' configuration section?

Accepted Answer

name. In the cloud-init 'users' configuration section, the 'name' directive (A) is valid and required, as it defines the login name of the user account to be created. The 'ssh_authorized_keys' directive (B) is also valid, allowing a list of public SSH keys to be injected into the user's ~/.ssh/authorized_keys file for passwordless authentication. The 'groups' directive (E) is valid as well, specifying a list of supplementary groups to which the user should be added. The 'expiration_date' option (C) is not a recognized cloud-init user directive; account expiration is handled via the 'expire' directive (or 'expiredate' in some schemas), not 'expiration_date'. The 'security_level' option (D) is not part of the cloud-init users schema at all and has no meaning in this context.

Answer

expiration_date

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security_level

Question 10

What is the purpose of the virtio-balloon driver in a guest?

Accepted Answer

To enable memory ballooning. The virtio-balloon driver enables memory ballooning, a technique that allows the hypervisor to dynamically adjust the amount of memory allocated to a guest. The driver inflates or deflates a 'balloon' inside the guest, reclaiming or returning memory pages to the host. This helps optimize memory usage across VMs. It does not speed up network transfers, provide disk caching, or enable 3D graphics.

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To speed up network transfers

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To provide disk caching

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To enable 3D graphics