XK0-006 Automation, Orchestration, and Scripting Practice Question
Which Dockerfile instruction sets the command to run when the container starts, but allows the user to override it when using docker run?
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
✓
CMD
CMD provides defaults for an executing container. If CMD is used, it can be overridden by command-line arguments to docker run. ENTRYPOINT, on the other hand, is not easily overridden without --entrypoint.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
RUN
Why it's wrong here
RUN executes commands during image build, committing the results as a new layer; it has no effect on what starts when the container launches. It is tempting because it runs a command, but it would be correct for installing packages or compiling software at build time, whereas CMD supplies the overridable runtime command.
- ✗
STARTUP
Why it's wrong here
STARTUP is not a valid Dockerfile instruction, so the build fails rather than setting a container command. It is tempting because the name suggests initialisation behaviour, but the correct instruction for a default, overridable start command is CMD, which docker run arguments replace; ENTRYPOINT sets a non-overridable executable.
- ✗
ENTRYPOINT
Why it's wrong here
ENTRYPOINT defines the fixed executable, so docker run arguments are appended as parameters rather than replacing it; overriding requires --entrypoint. It is tempting because ENTRYPOINT suits containers that must always run one specific process, such as a database daemon, where CMD supplies only default arguments.
- ✓
CMD
Why this is correct
CMD sets the default command executed when the container starts, but it is overridden when arguments are supplied to docker run. ENTRYPOINT, by contrast, is not overridden this way, so CMD matches the stated requirement.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.