This CKS practice question tests your understanding of cluster hardening. 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 is failing to start with: 'Error: container has runAsNonRoot and image will run as root'. The pod spec sets securityContext.runAsNonRoot: true. The container image is 'nginx:latest' which runs as root. Which change allows the pod to run while maintaining security?
Remove runAsNonRoot: true
Why wrong: This relaxes security.
Add a PodSecurityPolicy that allows root
Why wrong: PSP is deprecated and not the direct fix.
Set runAsUser: 1000 in the container securityContext
Runs as non-root user, satisfying runAsNonRoot.
Use a mutating webhook to change the image
Why wrong: Too complex and not immediate.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Set runAsUser: 1000 in the container securityContext
Option C is correct because setting `runAsUser: 1000` in the container's securityContext overrides the default user (root) in the image, ensuring the container process runs as a non-root user (UID 1000). This satisfies the `runAsNonRoot: true` constraint at the pod level, which requires that the container's user ID is non-zero, while still maintaining security by not running as root.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Remove runAsNonRoot: true
Why it's wrong here
This relaxes security.
Add a PodSecurityPolicy that allows root
Why it's wrong here
PSP is deprecated and not the direct fix.
Set runAsUser: 1000 in the container securityContext
Why this is correct
Runs as non-root user, satisfying runAsNonRoot.
Related concept
Read the scenario before looking for a memorised answer.
Use a mutating webhook to change the image
Why it's wrong here
Too complex and not immediate.
Common exam traps
CNCF often tests the distinction between pod-level and container-level securityContext settings, and the trap here is that candidates might think removing `runAsNonRoot` or using a deprecated PSP is acceptable, rather than directly setting a non-root user ID in the container's securityContext.
Detailed technical explanation
The `runAsNonRoot: true` field in the pod or container securityContext enforces that the container's user ID (UID) must not be 0 (root). When set at the pod level, it applies to all containers unless overridden at the container level. The `nginx:latest` image runs as root (UID 0) by default, so setting `runAsUser: 1000` in the container securityContext changes the effective UID to 1000, which is non-root, satisfying the constraint. Under the hood, Kubernetes uses the `securityContext` to set the `RunAsUser` field in the container's `SecurityContext` object, which is passed to the container runtime (e.g., containerd) to configure the process's UID via the `user` namespace or `setuid` syscall.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Cluster Hardening — This question tests Cluster Hardening — Read the scenario before looking for a memorised answer..
The correct answer is: Set runAsUser: 1000 in the container securityContext — Option C is correct because setting `runAsUser: 1000` in the container's securityContext overrides the default user (root) in the image, ensuring the container process runs as a non-root user (UID 1000). This satisfies the `runAsNonRoot: true` constraint at the pod level, which requires that the container's user ID is non-zero, while still maintaining security by not running as root.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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