- A
The container will be automatically restarted by the kubelet
Why wrong: Restart behavior depends on restart policy, but the immediate effect is a write failure.
- B
The write succeeds because logs are written to a temporary filesystem
Why wrong: There is no temporary filesystem by default; the container root is read-only.
- C
The write to /var/log/app.log fails, and the container may crash or log an error
The immutable filesystem prevents writes to the root filesystem; /var/log/ is part of the root filesystem unless a volume is mounted.
- D
Kubernetes will create an emptyDir volume to hold the logs
Why wrong: Kubernetes does not automatically create emptyDir volumes; the user must define them in the pod spec.
Question 587 of 997
How readOnlyRootFilesystem Affects Application Log Writes
This CKS practice question tests your understanding of monitoring, logging and runtime security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
A pod is running in the 'default' namespace with a container that has an immutable root filesystem (readOnlyRootFilesystem: true). The application writes logs to /var/log/app.log. What will happen?
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
✓
The write to /var/log/app.log fails, and the container may crash or log an error
When a container is configured with `readOnlyRootFilesystem: true`, its entire root filesystem is mounted as read-only. Since `/var/log/app.log` resides within the root filesystem, any attempt to write to it will fail with a permission error. This can cause the application to crash or log an error, depending on how the application handles write failures.
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.
- ✗
The container will be automatically restarted by the kubelet
Why it's wrong here
Restart behavior depends on restart policy, but the immediate effect is a write failure.
- ✗
The write succeeds because logs are written to a temporary filesystem
Why it's wrong here
There is no temporary filesystem by default; the container root is read-only.
- ✓
The write to /var/log/app.log fails, and the container may crash or log an error
Why this is correct
The immutable filesystem prevents writes to the root filesystem; /var/log/ is part of the root filesystem unless a volume is mounted.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Kubernetes will create an emptyDir volume to hold the logs
Why it's wrong here
Kubernetes does not automatically create emptyDir volumes; the user must define them in the pod spec.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The CKS exam often tests the misconception that Kubernetes automatically handles logging by providing writable space, but in reality, the user must explicitly mount a writable volume when using a read-only root filesystem.
Detailed technical explanation
How to think about this question
Under the hood, `readOnlyRootFilesystem: true` sets the `ReadonlyRootfs` field in the container's `SecurityContext`, which causes the container runtime (e.g., containerd) to mount the rootfs with the `MS_RDONLY` flag. A common real-world scenario is that applications expecting to write logs to `/var/log` will fail silently or crash unless a writable volume (like an `emptyDir` or `hostPath`) is mounted at that location. This is a frequent misconfiguration in security-hardened clusters.
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.
- →
Monitoring, Logging and Runtime Security — study guide chapter
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FAQ
Questions learners often ask
What does this CKS question test?
Monitoring, Logging and Runtime Security — This question tests Monitoring, Logging and Runtime Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The write to /var/log/app.log fails, and the container may crash or log an error — When a container is configured with `readOnlyRootFilesystem: true`, its entire root filesystem is mounted as read-only. Since `/var/log/app.log` resides within the root filesystem, any attempt to write to it will fail with a permission error. This can cause the application to crash or log an error, depending on how the application handles write failures.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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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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