- A
Use a ConfigMap volume with defaultMode 0444
Why wrong: Setting defaultMode on a ConfigMap volume only affects file permissions; the volume is still writable unless mounted with readOnly: true. Even with readOnly: true, only that specific volume is read-only, not the container's root filesystem.
- B
Set readOnly: true on a hostPath volume mount
Why wrong: Setting readOnly: true on a hostPath volume mount restricts writes to that hostPath, but the container's own filesystem remains writable.
- C
Set readOnlyRootFilesystem: true in the container's securityContext
Correct. readOnlyRootFilesystem: true in the securityContext makes the entire container root filesystem read-only.
- D
Mount an emptyDir volume with readOnly: true
Why wrong: Mounting an emptyDir volume with readOnly: true makes only that specific mount point read-only; the container's root filesystem remains writable. This does not achieve a read-only container filesystem.
Setting readOnlyRootFilesystem: true vs Volume-Level Read-Only: CKS Exam Guide
This CKS practice question tests your understanding of minimize microservice vulnerabilities. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which TWO of the following are valid methods to restrict a container's filesystem to read-only in Kubernetes?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Set readOnlyRootFilesystem: true in the container's securityContext
Option C is the only valid method listed. Setting `readOnlyRootFilesystem: true` in the container's securityContext directly makes the container's root filesystem read-only. Options A, B, and D only make specific volumes read-only (ConfigMap, hostPath, emptyDir), but do not prevent writes to the container's own filesystem (e.g., /etc, /tmp, /var). Therefore, only option C correctly restricts the container's filesystem to read-only.
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.
- ✗
Use a ConfigMap volume with defaultMode 0444
Why it's wrong here
Setting defaultMode on a ConfigMap volume only affects file permissions; the volume is still writable unless mounted with readOnly: true. Even with readOnly: true, only that specific volume is read-only, not the container's root filesystem.
- ✗
Set readOnly: true on a hostPath volume mount
Why it's wrong here
Setting readOnly: true on a hostPath volume mount restricts writes to that hostPath, but the container's own filesystem remains writable.
- ✓
Set readOnlyRootFilesystem: true in the container's securityContext
Why this is correct
Correct. readOnlyRootFilesystem: true in the securityContext makes the entire container root filesystem read-only.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Mount an emptyDir volume with readOnly: true
Why it's wrong here
Mounting an emptyDir volume with readOnly: true makes only that specific mount point read-only; the container's root filesystem remains writable. This does not achieve a read-only container filesystem.
Common exam traps
Common exam trap: answer the scenario, not the keyword
In the CKS exam, the distinction between making a specific volume read-only (e.g., via `readOnly: true` on a mount) versus making the entire container's root filesystem read-only via `readOnlyRootFilesystem` is often tested. Candidates mistakenly think that setting `readOnly: true` on any volume achieves the same effect.
Detailed technical explanation
How to think about this question
Under the hood, `readOnlyRootFilesystem: true` leverages the Linux kernel's mount namespace and the `MS_RDONLY` flag to remount the container's root filesystem as read-only after the container is started. This is enforced by the OCI runtime (e.g., runc) and is independent of any volume mounts; it prevents writes to `/`, `/etc`, `/var`, etc., but does not affect writable volumes like emptyDir or hostPath that are explicitly mounted. In real-world scenarios, this setting is often combined with an emptyDir volume for temporary write space (e.g., for logs or scratch data) to achieve a 'mostly read-only' container while still allowing necessary ephemeral writes.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Minimize Microservice Vulnerabilities — study guide chapter
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FAQ
Questions learners often ask
What does this CKS question test?
Minimize Microservice Vulnerabilities — This question tests Minimize Microservice Vulnerabilities — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set readOnlyRootFilesystem: true in the container's securityContext — Option C is the only valid method listed. Setting `readOnlyRootFilesystem: true` in the container's securityContext directly makes the container's root filesystem read-only. Options A, B, and D only make specific volumes read-only (ConfigMap, hostPath, emptyDir), but do not prevent writes to the container's own filesystem (e.g., /etc, /tmp, /var). Therefore, only option C correctly restricts the container's filesystem to read-only.
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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Last reviewed: Jul 4, 2026
This CKS practice question is part of Courseiva's free CNCF certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CKS exam.
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