Quick Answer
The answer is to combine multiple RUN commands into a single RUN instruction. This is the most effective practice for reducing Docker image size because each RUN command creates a new layer in the image, and intermediate files like package caches are preserved across those separate layers, bloating the final footprint. By merging commands into one RUN statement, you ensure that temporary artifacts are cleaned up within the same layer, so they never persist in the final image. On the CompTIA Linux+ XK0-005 exam, this concept tests your understanding of Docker layer caching and image optimization, often appearing as a distractor where candidates mistakenly choose to use a smaller base image or add a cleanup step after each RUN. The common trap is thinking that adding `rm -rf` after each install is enough, but those deletions still exist in a prior layer. Remember the mnemonic: one RUN to rule them all—fewer layers, smaller payload.
This XK0-005 practice question tests your understanding of scripting, containers and automation. 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.
A developer writes a Dockerfile that installs multiple packages. To reduce the final image size, which of the following practices is most effective?
Use a multi-stage build.
Why wrong: Multi-stage is effective but not directly about combining RUN commands.
Combine multiple RUN commands into a single RUN instruction.
Reduces number of layers, decreasing image size.
Use apt-get clean after each installation.
Why wrong: Only cleans cache, doesn't reduce layers.
Use a minimal base image like alpine.
Why wrong: Good practice but not about combining instructions.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Combine multiple RUN commands into a single RUN instruction.
Combining multiple RUN commands into a single RUN instruction reduces the number of layers created in the Docker image. Each RUN instruction creates a new layer, and by merging them, you avoid storing intermediate files (e.g., package cache) across separate layers, which significantly shrinks the final image size. This is a direct and effective method for minimizing image footprint when installing multiple packages.
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.
Use a multi-stage build.
Why it's wrong here
Multi-stage is effective but not directly about combining RUN commands.
Combine multiple RUN commands into a single RUN instruction.
Why this is correct
Reduces number of layers, decreasing image size.
Related concept
Read the scenario before looking for a memorised answer.
Use apt-get clean after each installation.
Why it's wrong here
Only cleans cache, doesn't reduce layers.
Use a minimal base image like alpine.
Why it's wrong here
Good practice but not about combining instructions.
Common exam traps
CompTIA often tests the misconception that using a minimal base image or cleaning up in separate steps is sufficient, when in fact the layer persistence model means only combining RUN commands (and cleaning within the same layer) truly eliminates intermediate file bloat.
Trap categories for this question
Command / output trap
Multi-stage is effective but not directly about combining RUN commands.
Detailed technical explanation
Docker images are composed of read-only layers, each representing a filesystem change. When you use separate RUN commands, each creates a new layer that persists even if intermediate files (e.g., /var/cache/apt/archives) are deleted later, because the deletion only marks the space as free in the new layer, not in the previous ones. By combining commands with '&&', all operations occur in a single layer, so cleanup commands like apt-get clean actually remove the cached files from that same layer, preventing them from being part of the final image. This is why the Docker best practice guide explicitly recommends chaining package installations and cleanups in one RUN instruction.
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 XK0-005 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Scripting, Containers and Automation — study guide chapter
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FAQ
Scripting, Containers and Automation — This question tests Scripting, Containers and Automation — Read the scenario before looking for a memorised answer..
The correct answer is: Combine multiple RUN commands into a single RUN instruction. — Combining multiple RUN commands into a single RUN instruction reduces the number of layers created in the Docker image. Each RUN instruction creates a new layer, and by merging them, you avoid storing intermediate files (e.g., package cache) across separate layers, which significantly shrinks the final image size. This is a direct and effective method for minimizing image footprint when installing multiple packages.
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
This XK0-005 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 XK0-005 exam.
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