This CKS practice question tests your understanding of system hardening. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are a platform engineer for a financial services company. Your Kubernetes cluster runs on bare-metal nodes with Ubuntu 20.04 and uses containerd as the container runtime. The cluster is in production with 50 worker nodes. A recent security scan shows that all nodes have the 'overlayfs' kernel module loaded, which is not required. The security policy requires minimal kernel modules. You need to disable the module without disrupting running containers. What should you do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add 'blacklist overlayfs' to /etc/modprobe.d/ and run 'update-initramfs -u', then reboot nodes one by one after draining
Option B is correct because it permanently disables the overlayfs kernel module by adding it to the modprobe blacklist and updating the initramfs, ensuring the module is not loaded on subsequent boots. Draining and rebooting nodes one by one avoids disrupting running containers, as pods are rescheduled to other nodes before the node is taken offline. This approach aligns with the security policy of minimizing kernel modules while maintaining production uptime.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Restart containerd on each node to unload the module
Why it's wrong here
Restarting containerd would kill all containers.
✓
Add 'blacklist overlayfs' to /etc/modprobe.d/ and run 'update-initramfs -u', then reboot nodes one by one after draining
Why this is correct
This ensures the module is not loaded on subsequent boots, and draining before reboot prevents disruption.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use 'rmmod overlayfs' after stopping all containers
Why it's wrong here
Stopping all containers is disruptive and 'rmmod' does not prevent re-loading on reboot.
✗
Use 'modprobe -r overlayfs' on each node immediately
Why it's wrong here
Removing a module in use by containerd would break running containers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CNCF often tests the misconception that unloading a kernel module with 'rmmod' or 'modprobe -r' is safe while containers are running, but in reality, overlayfs is actively used by the container runtime and cannot be removed without causing filesystem errors or container crashes.
Detailed technical explanation
How to think about this question
The overlayfs kernel module is used by container runtimes like containerd to provide overlay filesystem layers for container images. Even if the module is not required by the security policy, it may be loaded automatically by the kernel at boot or when containerd starts; blacklisting it in modprobe.d prevents auto-loading, and update-initramfs -u rebuilds the initial ramdisk to exclude the module. In a production cluster, draining a node (kubectl drain) evicts all pods gracefully, then rebooting loads the kernel without overlayfs, and after the node rejoins, containerd can fall back to other snapshotter drivers (e.g., devicemapper or native) if configured, though this may require runtime reconfiguration.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the CKS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CKS question in full detail.
System Hardening — This question tests System Hardening — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add 'blacklist overlayfs' to /etc/modprobe.d/ and run 'update-initramfs -u', then reboot nodes one by one after draining — Option B is correct because it permanently disables the overlayfs kernel module by adding it to the modprobe blacklist and updating the initramfs, ensuring the module is not loaded on subsequent boots. Draining and rebooting nodes one by one avoids disrupting running containers, as pods are rescheduled to other nodes before the node is taken offline. This approach aligns with the security policy of minimizing kernel modules while maintaining production uptime.
What should I do if I get this CKS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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