This CKAD practice question tests your understanding of application design and build. 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.
Which of the following Dockerfile instructions is used to set a command that runs when the container starts and can be overridden by command-line arguments?
EXPOSE
Why wrong: EXPOSE documents ports, does not run anything.
CMD
CMD provides defaults for an executing container; it can be overridden by providing command-line arguments to docker run.
COPY
Why wrong: COPY copies files into the image, does not set the startup command.
RUN
Why wrong: RUN executes commands during image build, not at container start.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
CMD
Option B is correct. CMD sets the default command that can be overridden. ENTRYPOINT sets the command that cannot be overridden (unless --entrypoint flag is used). Option A (RUN) runs during image build. Option C (EXPOSE) documents ports. Option D (COPY) copies files.
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.
EXPOSE
Why it's wrong here
EXPOSE documents ports, does not run anything.
CMD
Why this is correct
CMD provides defaults for an executing container; it can be overridden by providing command-line arguments to docker run.
Related concept
Read the scenario before looking for a memorised answer.
COPY
Why it's wrong here
COPY copies files into the image, does not set the startup command.
RUN
Why it's wrong here
RUN executes commands during image build, not at container start.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
COPY copies files into the image, does not set the startup command.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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 CKAD 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
Identify which CKAD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Application Design and Build — This question tests Application Design and Build — Read the scenario before looking for a memorised answer..
The correct answer is: CMD — Option B is correct. CMD sets the default command that can be overridden. ENTRYPOINT sets the command that cannot be overridden (unless --entrypoint flag is used). Option A (RUN) runs during image build. Option C (EXPOSE) documents ports. Option D (COPY) copies files.
Identify which CKAD exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 21, 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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