This CKS practice question tests your understanding of cluster hardening. 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.
An administrator wants to prevent pods from running as root. Which SecurityContext field should be set at the pod level?
fsGroup: 2000
Why wrong: Sets filesystem group for volumes.
runAsGroup: 3000
Why wrong: Only sets group ID.
runAsUser: 1000
Why wrong: Sets a specific user, but could be root if set to 0.
runAsNonRoot: true
Explicitly prevents root.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
runAsNonRoot: true
Option D is correct because setting `runAsNonRoot: true` at the pod-level SecurityContext enforces that all containers in the pod must run with a non-root user (UID > 0). If a container image specifies a user with UID 0 (root) or does not specify a user, the container will fail to start, preventing privilege escalation from root access.
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.
fsGroup: 2000
Why it's wrong here
Sets filesystem group for volumes.
runAsGroup: 3000
Why it's wrong here
Only sets group ID.
runAsUser: 1000
Why it's wrong here
Sets a specific user, but could be root if set to 0.
runAsNonRoot: true
Why this is correct
Explicitly prevents root.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
CNCF often tests the distinction between setting a specific user ID (runAsUser) and enforcing a non-root requirement (runAsNonRoot), where candidates mistakenly think that setting runAsUser to a non-zero value alone prevents root execution, but it does not block an image that runs as root by default if runAsUser is omitted or set to 0.
Detailed technical explanation
Under the hood, `runAsNonRoot: true` triggers a security check in the kubelet's PodSecurityContext validation: it verifies that the container's effective UID (from the image's USER directive or `runAsUser`) is not 0. If the image has no USER directive and `runAsUser` is not set, the container defaults to root (UID 0) and will be rejected. This is critical in multi-tenant clusters where images from untrusted registries might run as root, and using `runAsNonRoot` at the pod level provides a blanket enforcement without needing to know the specific UID.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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: runAsNonRoot: true — Option D is correct because setting `runAsNonRoot: true` at the pod-level SecurityContext enforces that all containers in the pod must run with a non-root user (UID > 0). If a container image specifies a user with UID 0 (root) or does not specify a user, the container will fail to start, preventing privilege escalation from root access.
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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