305-300 Practice Test 11 — 15 Questions

Question 1

You need to create a new storage pool for KVM guests using the virsh command-line tool. The pool should use a directory on the host filesystem at /var/lib/libvirt/images/extra. Which command correctly defines and starts this pool?

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

Accepted Answer

virsh pool-define-as extra dir --target /var/lib/libvirt/images/extra && virsh pool-start extra. To create a persistent directory-based storage pool, you use virsh pool-define-as with the pool name, type 'dir', and the target path. Then you start it with virsh pool-start. This ensures the pool is defined in libvirt's configuration and is immediately available for use. The pool-create-as command creates a transient pool that is lost on reboot, which is not suitable for a permanent addition.

Answer

virsh pool-create-as extra dir --target /var/lib/libvirt/images/extra

Answer

virsh pool-define extra --type dir --path /var/lib/libvirt/images/extra && virsh pool-start extra

Answer

virsh pool-add extra dir /var/lib/libvirt/images/extra && virsh pool-start extra

Question 2

You are running a Podman container as a non-root user with rootless mode. The container needs to bind to TCP port 80 inside the container's network namespace so a legacy application can listen for HTTP traffic. Which capability must be added to the container to allow binding to this privileged port without running the container as root?

Accepted Answer

CAP_NET_BIND_SERVICE. Binding to ports below 1024 requires the CAP_NET_BIND_SERVICE capability when the process does not have root privileges. In rootless Podman, the container process is mapped to an unprivileged user, so the kernel denies the bind on port 80 unless this capability is explicitly added. The other capabilities listed address unrelated privilege areas and would not resolve the bind failure.

Answer

CAP_NET_ADMIN

Answer

CAP_DAC_OVERRIDE

Answer

CAP_SYS_ADMIN

Question 3

You are using cloud-init to configure a VM that must run a script only on the very first boot, and the script must not run again on subsequent reboots. The script is provided as a MIME part in a multipart user-data file. Which cloud-init module should be used to ensure this behavior?

Accepted Answer

scripts-per-instance. Cloud-init's scripts-per-instance module executes scripts only on the first boot of an instance. It is intended for one-time provisioning tasks. In a multipart user-data file, scripts can be included with a content type that cloud-init recognizes for per-instance execution. Other modules like bootcmd or runcmd run on every boot, and scripts-per-boot is explicitly for every boot. Therefore, scripts-per-instance is the correct module.

Answer

bootcmd

Answer

scripts-per-boot

Answer

runcmd

Question 4

You are troubleshooting a Docker container that fails to start with the error 'no space left on device' even though `df -h` shows ample free space on the host's root filesystem. The Docker data root is on a separate partition. Which command should you use to check the actual disk usage of Docker's data root?

Accepted Answer

`docker system df -v`. `docker system df -v` reports detailed disk usage for images, containers, volumes, and build cache. When the Docker data root resides on a separate partition, the host's `df` may show free space elsewhere. This command exposes the actual consumption within Docker's storage, allowing you to identify whether images, volumes, or cache are filling the partition.

Answer

`docker events`

Answer

`docker stats`

Answer

`docker info`

Question 5

A production KVM guest uses a virtio-blk disk and experiences periodic I/O stalls during heavy write bursts. You want to switch the guest disk to virtio-scsi with multiple queues to improve parallelism without reinstalling the guest OS. Which change should you make to the domain XML?

Accepted Answer

Add a <controller type='scsi' model='virtio-scsi'/> with queues='4' and change the disk target bus to scsi.. Virtio-scsi multi-queue is enabled by adding queues to the virtio-scsi controller element and attaching the disk to that controller through its target bus. This gives the guest multiple virtqueues for parallel I/O processing, which reduces stalls during write bursts. The other options either misuse the queues attribute, change image formats without addressing parallelism, or introduce a network block backend that does not provide the requested feature.

Answer

Add <driver name='qemu' type='qcow2' queues='4'/> to the existing virtio-blk disk and restart the guest.

Answer

Set <driver name='qemu' type='raw' cache='none' io='native'/> on the disk and increase the guest's nr_requests.

Answer

Replace the disk with <disk type='network' device='disk'> using an NBD backend exported by the host.

Question 6

You are managing a KVM host and need to create a new storage pool that uses a directory on the host filesystem to store disk images. After creating the directory /var/lib/libvirt/images/extra, you want to define and start a libvirt storage pool named 'extra-pool' that uses this directory. Which sequence of virsh commands accomplishes this?

Accepted Answer

virsh pool-define-as extra-pool dir --target /var/lib/libvirt/images/extra; virsh pool-start extra-pool. The correct approach is to define a persistent directory-based pool using pool-define-as with type dir and the target path, then start it with pool-start. This creates a reusable pool definition and activates it immediately. Using pool-create-as would only create a transient pool, and the other commands either target volumes or use the wrong pool type.

Answer

virsh pool-create-as extra-pool dir --target /var/lib/libvirt/images/extra

Answer

virsh vol-create-as extra-pool /var/lib/libvirt/images/extra 10G

Answer

virsh pool-define-as extra-pool logical --target /var/lib/libvirt/images/extra

Question 7

You are troubleshooting a KVM guest that fails to boot after you changed its XML configuration. You want to verify and correct the guest's definition without starting it. Which TWO of the following actions are appropriate? (Choose two.)

Accepted Answer

Use virsh define /path/to/guest.xml to update the persistent domain definition from an edited XML file.. To correct a guest's persistent XML without starting it, you can either edit the XML directly with virsh edit, which validates before saving, or prepare an edited XML file and apply it with virsh define. Both update the persistent definition. Using virsh create would only start a transient guest, and undefining is destructive and unnecessary.

Answer

Use virsh undefine guestname then virsh define guest.xml to replace the configuration.

Answer

Use virsh dumpxml guestname > guest.xml, edit the file, then run virsh create guest.xml to apply changes persistently.

Answer

Use virsh start guestname --validate to check the XML and start the guest if valid.

Question 8

You are building a Docker image and want to ensure that a build-time variable is available only during the build, not persisted in the final image's environment. Which instruction should you use?

Accepted Answer

ARG. `ARG` is designed for values that are needed only while building the image. It can be supplied with `--build-arg` and is not stored in the final image's environment. `ENV` would persist the value, while `LABEL` and `EXPOSE` serve unrelated metadata and port documentation purposes. Only the build-argument instruction meets the requirement of a transient build-time variable.

Answer

ENV

Answer

LABEL

Answer

EXPOSE

Question 9

A Packer template targets the qemu builder to produce a KVM-compatible image. The build completes without error, but when the resulting qcow2 file is booted with `qemu-system-x86_64 -drive file=image.qcow2,if=virtio`, the guest kernel panics with "VFS: Unable to mount root fs" because it cannot see any block device. The template defines only `iso_url`, `iso_checksum`, `ssh_username`, and `ssh_password`. Which change to the template is MOST likely to resolve this?

Accepted Answer

Add a `boot_command` that boots the installer with `inst.modprobe=virtio_blk` (or install a kernel/initramfs that includes the virtio_blk module) so the guest can see the virtio disk.. The failure is a guest-side driver problem, not a builder configuration problem. Packer's qemu builder already presents the disk as virtio-blk, and the host-side QEMU command line uses `if=virtio`, so the guest must have the virtio_blk module available in its initramfs to mount the root filesystem. Adding the module through the installer boot command, or rebuilding the initramfs to include it, restores visibility of the disk and resolves the panic.

Answer

Add `disk_interface = "virtio"` to the builder's configuration so the disk controller matches the boot command line.

Answer

Add `qemuargs = [["-device", "virtio-blk-pci"]]` to force an explicit virtio controller during the build.

Answer

Set `format` to `raw` so the disk is written as a plain image instead of qcow2.

Question 10

You maintain a Vagrant environment where a single Vagrantfile defines three web servers and one database server. You need each web server to use a different forwarded SSH port on the host because port 2222 is already taken by another project. Which approach correctly assigns unique host ports per machine?

Accepted Answer

Add a separate config.vm.network "forwarded_port", guest: 22, host: 2201, id: "ssh" line inside each machine's config block.. Multi-machine Vagrantfiles give each machine its own configuration block, and SSH port forwarding must be defined there to avoid collisions. Using the forwarded_port directive with guest: 22, a unique host port, and a stable id ensures each web server is reachable on a distinct host port while the database server keeps its own mapping. Global settings or hostname changes do not produce unique host ports.

Answer

Use config.vm.provider "virtualbox" do |vb| vb.customize ["modifyvm", :id, "--natpf1", "ssh,tcp,,2201,,22"] end once in the global scope.

Answer

Set config.ssh.port = 2201 once at the top level of the Vagrantfile, outside any machine block.

Answer

Add config.vm.hostname = "web1" to each machine and rely on Vagrant to derive unique SSH ports automatically.

Question 11

A KVM host runs libvirt with a default storage pool at /var/lib/libvirt/images. You need to create a new qcow2-backed volume named 'app-disk.qcow2' with a virtual size of 40 GB inside the pool named 'default'. Which single virsh command accomplishes this?

Accepted Answer

virsh vol-create-as default app-disk.qcow2 40G --format qcow2. The virsh vol-create-as subcommand is purpose-built for creating a volume inside an existing storage pool with a specified name, capacity, and format. Supplying the pool name, volume name, size, and --format qcow2 produces a qcow2-backed image of the requested virtual size. The other commands either target pools instead of volumes, expect XML input, or attempt to clone a nonexistent source.

Answer

virsh vol-clone app-disk.qcow2 default --capacity 40G --format qcow2

Answer

virsh pool-create-as default app-disk.qcow2 40G --format qcow2

Answer

virsh vol-create default --name app-disk.qcow2 --capacity 40G --format qcow2

Question 12

You are building a Docker image and need to ensure that the container process runs as a non-root user with UID 1000 and that this user exists in the image. Which pair of Dockerfile instructions achieves this correctly?

Accepted Answer

`RUN useradd -u 1000 -m appuser` followed by `USER appuser`. The user must exist before it can be selected. Creating it with `useradd` while the build still runs as root, then switching with `USER appuser`, ensures the account is present in /etc/passwd and that the container process runs with the intended non-root identity. Reversing the order or using a numeric UID without creating the account leads to failures or reduced clarity.

Answer

`USER appuser` followed by `RUN useradd -u 1000 appuser`

Answer

`USER 1000` followed by `RUN useradd -u 1000 appuser`

Answer

`RUN useradd -u 1000 appuser` followed by `USER 1000`

Question 13

You are preparing a KVM guest for a maintenance window and need to shut it down gracefully so the guest OS can flush buffers and stop services. Which virsh command should you use?

Accepted Answer

virsh shutdown guest1. A graceful shutdown requires notifying the guest OS so it can stop services and flush buffers. The shutdown subcommand does this via ACPI or the guest agent. destroy is a forced power-off, suspend is a pause, and undefine removes configuration, so none of those provide an orderly halt.

Answer

virsh destroy guest1

Answer

virsh undefine guest1

Answer

virsh suspend guest1

Question 14

You are managing a KVM host and need to gracefully shut down a running guest named 'dbserver'. Which virsh command should you use?

Accepted Answer

virsh shutdown dbserver. The virsh shutdown command sends an ACPI shutdown request to the guest, allowing the guest operating system to perform a clean shutdown. This is the preferred method for gracefully stopping a virtual machine. The virsh destroy command forcibly powers off the guest, which can cause data loss. The other options are not valid virsh commands.

Answer

virsh stop dbserver

Answer

virsh destroy dbserver

Answer

virsh halt dbserver

Question 15

A developer wants to run a short-lived container that executes a command and then removes itself automatically after exit. Which `docker run` flag should be used?

Accepted Answer

`--rm`. `--rm` is specifically designed to remove the container automatically when it exits. It is commonly used for one-off commands and CI jobs. The other flags control background execution, STDIN, or TTY allocation, none of which affect post-exit cleanup. Only `--rm` ensures the container does not linger after its task finishes.

Answer

`--detach`

Answer

`--interactive`

Answer

`--tty`