305-300 Practice Test 15 — 15 Questions

Question 1

What is the purpose of the 'virt-install' tool?

Accepted Answer

Provisioning new virtual machines. virt-install is a command-line tool from the virt-manager suite used to provision new virtual machines on libvirt-managed hypervisors. It creates the domain XML, allocates resources (CPU, memory, disk, network), and starts the guest in one operation, optionally launching an installation via PXE, ISO, or network boot. Its core purpose is VM creation, not post-creation management.

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Migrating virtual machines

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Monitoring VM performance

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Editing VM XML

Question 2

When configuring a systemd-nspawn container, what is the effect of the --private-network option?

Accepted Answer

It isolates the container's network from the host. The --private-network option in systemd-nspawn creates a new, isolated network namespace for the container. This means the container gets its own loopback interface and no external network interfaces, completely separating its network stack from the host's. As a result, the container cannot communicate with the host or external networks unless additional virtual interfaces are configured.

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It forces the container to use a bridge

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It disables network encryption

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It restricts access to localhost

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It prevents the container from starting

Question 3

A Docker container running a web server is unable to serve traffic on port 8080. You verify the Dockerfile exposes port 80. What is the correct way to map this for external access?

Accepted Answer

docker run -p 8080:80. The -p flag syntax is HOST_PORT:CONTAINER_PORT. Since the web server inside the container listens on port 80 (per the Dockerfile EXPOSE), and you want it reachable on host port 8080, the correct mapping is -p 8080:80 — host 8080 forwards to container 80. Docker's userland proxy or iptables DNAT rules then translate incoming traffic on the host's 8080 to the container's 80.

Answer

docker run -p 80:8080

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docker run --net host

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docker run --expose 8080

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docker run -P 8080

Question 4

You have a qcow2 disk image that is growing too large. You want to shrink the file size on the host while keeping the virtual disk the same size. Which steps must you perform first?

Accepted Answer

Run fstrim in the guest, then use qemu-img convert -O qcow2.. To shrink a qcow2 file on the host while keeping the virtual disk size unchanged, you must first reclaim unused blocks inside the guest by running fstrim (which issues TRIM/discard to the virtual disk), then compact the image with qemu-img convert -O qcow2, which rewrites only allocated clusters into a new sparse file. This two-step process is the standard method for reducing qcow2 on-disk footprint without altering the guest's visible disk capacity.

Answer

Delete files in the guest and use qemu-img resize.

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Use virsh blockpull.

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Use qemu-img check -r all.

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Run dd if=/dev/zero to fill the disk.

Question 5

Which THREE instructions in a Dockerfile can modify the image's filesystem?

Accepted Answer

ADD. ADD is correct because it copies files, directories, or remote URLs from the build context or a URL into the image filesystem, creating or modifying files in the resulting layer. RUN is correct because it executes a command in a new layer on top of the current image and commits the results, so commands like apt-get install or mkdir directly modify the image's filesystem. COPY is correct because it copies files or directories from the build context into the image filesystem, adding them as a new layer. ENV is not correct because it only sets environment variables in the image metadata and does not alter any files. EXPOSE is not correct because it only documents the intended network port in image metadata and does not change the filesystem.

Answer

ENV

Answer

EXPOSE

Question 6

You are configuring a Xen guest that requires direct hardware access to a specific network interface card. Which configuration parameter in the guest domain configuration file must be specified to enable PCI passthrough?

Accepted Answer

pci = [ '00:1f.1' ]. In Xen guest configuration files, PCI passthrough is enabled by specifying the 'pci' parameter with a list of PCI addresses, e.g., pci = [ '00:1f.1' ]. This directly assigns the physical PCI device to the guest.

Answer

device_pass = 'eth0'

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hw_access = '00:1f.1'

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vif = [ 'type=pci, bus=00:1f.1' ]

Question 7

When provisioning with Vagrant, which command is best used to apply changes to a configuration (like adding a new shell script) without destroying the existing virtual machine?

Accepted Answer

vagrant provision. The `vagrant provision` command is specifically designed to run provisioners (such as shell scripts, Ansible, Puppet, etc.) on a running Vagrant-managed VM without destroying or recreating it. When you modify a provisioning script or add a new one, `vagrant provision` applies those changes to the existing machine, ensuring the VM's state is updated according to the new configuration. This is the correct approach because it preserves the VM's current state while enforcing the updated provisioning logic.

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vagrant halt

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vagrant reload

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vagrant up

Question 8

You are configuring LXC and want to set a CPU limit for a container. Which cgroup parameter is used to specify the quota of CPU time in microseconds?

Accepted Answer

lxc.cgroup.cpu.cfs_quota_us. The cgroup CPU controller exposes the CFS (Completely Fair Scheduler) bandwidth control parameters cpu.cfs_quota_us and cpu.cfs_period_us. In LXC, these are set via the lxc.cgroup.cpu.cfs_quota_us key, which specifies the maximum CPU time (in microseconds) the container's tasks may consume within each period defined by cpu.cfs_period_us. Setting cfs_quota_us to 50000 with the default period of 100000 us effectively caps the container at 50% of one CPU core.

Answer

lxc.cgroup.cpu.limit

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lxc.cgroup.cpu.shares

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lxc.cgroup.cpu.period_us

Question 9

When configuring a VM in libvirt, you want to ensure the highest performance for disk I/O. Which driver type should you select for the disk device?

Accepted Answer

Virtio. Virtio is a paravirtualized driver framework designed specifically for KVM/QEMU guests, allowing the guest to communicate with the host through shared memory rings rather than emulating real hardware. For disk I/O, virtio-blk (or virtio-scsi) bypasses much of the emulation overhead of IDE/SATA/SCSI, delivering significantly higher throughput and lower CPU utilization. That makes 'virtio' the correct choice when the goal is maximum disk I/O performance in libvirt.

Answer

SCSI

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IDE

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SATA

Question 10

Which THREE features are provided by Linux Namespaces in the context of containers?

Accepted Answer

PID isolation. Linux namespaces provide PID isolation (C), giving each container its own process ID tree so processes inside see their own PID 1 and cannot see host processes. Network isolation (D) is provided by the network namespace, which gives a container its own network interfaces, routing tables, and ports. Mount isolation (E) is provided by the mount namespace, allowing each container its own filesystem mount points independent of the host. CPU scheduling (A) is handled by cgroups (cpu/cpuacct controllers), not namespaces, and disk quotas (B) are managed via filesystem quotas or cgroup blkio limits, not namespaces.

Answer

CPU scheduling

Answer

Disk quotas

Question 11

Which THREE settings are commonly configured in the 'provider' block of a Vagrantfile for virtualbox?

Accepted Answer

gui. In a Vagrantfile, the provider block for VirtualBox accepts the settings gui, cpus, and memory, which are all valid VirtualBox provider options. Option A (gui) is correct because it controls whether the VirtualBox VM launches with a graphical user interface, a common provider-specific setting. Option C (cpus) is correct because it sets the number of virtual CPUs allocated to the VM through the VirtualBox provider. Option E (memory) is correct because it specifies the amount of RAM in megabytes assigned to the VM by the VirtualBox provider. Option B (disk_size) is not a standard VirtualBox provider setting in Vagrant; disk resizing typically requires the vagrant-disksize plugin or manual VBoxManage commands. Option D (network_type) is not a valid Vagrant provider setting; networking is configured via config.vm.network with types like private_network or public_network.

Answer

disk_size

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network_type

Question 12

When using Vagrant to manage a libvirt-based provider, which command verifies that the virtual machine is currently running and identifies the provider in use?

Accepted Answer

vagrant status. The vagrant status command reports the current state of each machine defined in the Vagrantfile (running, poweroff, not created, etc.) and shows the provider in use (e.g., libvirt, virtualbox). It is the canonical way to verify that a VM is up and which provider is backing it.

Answer

vagrant up

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vagrant validate

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vagrant box list

Question 13

What does the 'docker rm' command do?

Accepted Answer

Removes a container. docker rm removes one or more containers from the host, deleting their writable layer and metadata. It does not touch images, does not stop running containers unless -f is used, and does not rename anything. This is the counterpart to docker rmi, which removes images.

Answer

Renames a container

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Stops a container

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Removes an image

Question 14

Which file is primarily responsible for defining the configuration and environment variables for an OpenVZ container?

Accepted Answer

/etc/vz/conf/CTID.conf. OpenVZ stores per-container configuration files in /etc/vz/conf/ using the container ID (CTID) as the filename, e.g., /etc/vz/conf/101.conf. This file defines resource limits, network settings, and environment variables for that specific container. The global OpenVZ configuration is in /etc/vz/vz.conf, but per-container settings live in the CTID.conf file.

Answer

/etc/openvz/config

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/var/lib/vz/config

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/etc/vz/container.conf

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/etc/vz/vz.conf

Question 15

You are using systemd-nspawn. How do you create an image of a container to be used as a template?

Accepted Answer

machinectl export-tar. machinectl export-tar is the systemd-nspawn command that exports a running or stopped container's filesystem as a tar archive, which can then be imported as a template image. It is part of the systemd-machined toolset and is the native way to snapshot an nspawn container for reuse.

Answer

tar -cvf

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docker export

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lxc-copy