Question 578 of 997

Monitoring, Logging and Runtime Security →easyMultiple ChoiceObjective-mapped

ReadOnlyRootFilesystem: Fixing /tmp Write Failures with emptyDir

This CKS practice question tests your understanding of monitoring, logging and runtime 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.

You have deployed a pod and set `securityContext.readOnlyRootFilesystem: true`. The pod is failing to start with an error about writing to `/tmp`. What is the most likely cause?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The `securityContext` is misspelled
Why wrong: Misspelling would cause a validation error, not a runtime write error.
B
The pod is missing an emptyDir volume mounted at `/tmp`
An emptyDir volume provides a writable location on an otherwise read-only root filesystem.
C
The container image does not have `/tmp` directory
Why wrong: Even if the directory exists, writing to it requires a writable filesystem.
D
The container is running as a non-root user
Why wrong: Non-root users can still write if the filesystem is writable; the issue is the read-only root filesystem.

Full breakdown with real-world context →

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 pod is missing an emptyDir volume mounted at `/tmp`

When `securityContext.readOnlyRootFilesystem: true` is set, the container's root filesystem becomes read-only. Many applications, including those that write temporary files, expect to write to `/tmp`. Without a writable volume mounted at `/tmp`, the container fails to start because it cannot write to that directory. Mounting an `emptyDir` volume at `/tmp` provides a writable location that is ephemeral and tied to the pod's lifecycle, resolving the issue.

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 `securityContext` is misspelled
Why it's wrong here
Misspelling would cause a validation error, not a runtime write error.
✓
The pod is missing an emptyDir volume mounted at `/tmp`
Why this is correct
An emptyDir volume provides a writable location on an otherwise read-only root filesystem.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The container image does not have `/tmp` directory
Why it's wrong here
Even if the directory exists, writing to it requires a writable filesystem.
✗
The container is running as a non-root user
Why it's wrong here
Non-root users can still write if the filesystem is writable; the issue is the read-only root filesystem.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The exam often tests the misconception that a read-only root filesystem prevents all writes, but candidates may overlook the need for an explicit writable volume mount like emptyDir for directories such as /tmp that applications expect to be writable.

Detailed technical explanation

How to think about this question

Under the hood, `readOnlyRootFilesystem: true` sets the container's root filesystem to read-only using the `overlay2` or `aufs` storage driver, preventing any writes to the root mount. An `emptyDir` volume is backed by a temporary filesystem (e.g., tmpfs on the node) and is mounted at `/tmp`, allowing the container to write there without affecting the read-only root. In real-world scenarios, applications like Java or Python interpreters often write temporary files to `/tmp`, so this is a common pitfall when enforcing read-only root filesystems.

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.

Visual reference

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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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 pod is missing an emptyDir volume mounted at `/tmp` — When `securityContext.readOnlyRootFilesystem: true` is set, the container's root filesystem becomes read-only. Many applications, including those that write temporary files, expect to write to `/tmp`. Without a writable volume mounted at `/tmp`, the container fails to start because it cannot write to that directory. Mounting an `emptyDir` volume at `/tmp` provides a writable location that is ephemeral and tied to the pod's lifecycle, resolving the issue.

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.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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