- A
The pod runs normally; Kubernetes automatically makes /tmp writable.
Why wrong: Kubernetes does not automatically make any directory writable. Only explicitly mounted volumes can be written to.
- B
The container crashes because it tries to write to /tmp but the filesystem is read-only.
The application will fail when trying to write to /tmp because the root filesystem is read-only.
- C
The pod is rejected by the admission controller because readOnlyRootFilesystem conflicts with writing to /tmp.
Why wrong: The admission controller does not check runtime behavior; it only validates the manifest.
- D
The container writes successfully because readOnlyRootFilesystem only applies to the container image layers.
Why wrong: readOnlyRootFilesystem applies to the entire root filesystem, including overlay filesystem layers.
CKAD Practice Question: Application Environment, Configuration and Security
This CKAD practice question tests your understanding of application environment, configuration and security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 has a container with 'readOnlyRootFilesystem: true' in its securityContext. The container writes to /tmp. What is the expected outcome?
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 container crashes because it tries to write to /tmp but the filesystem is read-only.
When `readOnlyRootFilesystem: true` is set in the container's securityContext, the root filesystem is mounted as read-only. The container writes to `/tmp`, which is part of the root filesystem by default, so the write fails and the container crashes (e.g., with an error like 'Read-only file system'). Kubernetes does not automatically make `/tmp` writable unless an explicit emptyDir volume is mounted at that path.
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 pod runs normally; Kubernetes automatically makes /tmp writable.
Why it's wrong here
Kubernetes does not automatically make any directory writable. Only explicitly mounted volumes can be written to.
- ✓
The container crashes because it tries to write to /tmp but the filesystem is read-only.
Why this is correct
The application will fail when trying to write to /tmp because the root filesystem is read-only.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The pod is rejected by the admission controller because readOnlyRootFilesystem conflicts with writing to /tmp.
Why it's wrong here
The admission controller does not check runtime behavior; it only validates the manifest.
- ✗
The container writes successfully because readOnlyRootFilesystem only applies to the container image layers.
Why it's wrong here
readOnlyRootFilesystem applies to the entire root filesystem, including overlay filesystem layers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume `/tmp` is always writable or that `readOnlyRootFilesystem` only affects the image layers, but in reality it makes the entire root filesystem read-only, causing runtime failures unless a writable volume is explicitly mounted at the write location.
Detailed technical explanation
How to think about this question
Under the hood, `readOnlyRootFilesystem: true` sets the root mount (/) to read-only via the container runtime (e.g., containerd or CRI-O), which affects all directories under it, including `/tmp`. A common workaround is to mount an emptyDir volume at `/tmp` to provide a writable scratch space, as emptyDir volumes are backed by a writable filesystem (e.g., tmpfs or node storage). This is a frequent pattern for containers that need to write temporary files while maintaining a read-only root for security.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
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Application Environment, Configuration and Security — study guide chapter
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FAQ
Questions learners often ask
What does this CKAD question test?
Application Environment, Configuration and Security — This question tests Application Environment, Configuration and Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The container crashes because it tries to write to /tmp but the filesystem is read-only. — When `readOnlyRootFilesystem: true` is set in the container's securityContext, the root filesystem is mounted as read-only. The container writes to `/tmp`, which is part of the root filesystem by default, so the write fails and the container crashes (e.g., with an error like 'Read-only file system'). Kubernetes does not automatically make `/tmp` writable unless an explicit emptyDir volume is mounted at that path.
What should I do if I get this CKAD 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
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Last reviewed: Jun 25, 2026
This CKAD 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 CKAD exam.
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