The answer is that the /tmp partition is using a small temporary disk separate from the persistent disk. On many Compute Engine images, /tmp is mounted as a tmpfs (in-memory filesystem), which draws from a fraction of the instance’s RAM rather than the attached persistent disk. When a batch job creates many large temporary files during processing, this tmpfs can fill up quickly, triggering a “No space left on device” error even when the persistent disk shows 100 GB free. This question tests your understanding of Compute Engine’s default filesystem layout, a common trap where developers assume all local storage is on the persistent disk. On the Google Professional Cloud Developer exam, always verify whether /tmp is a tmpfs or a disk-backed partition before troubleshooting disk space. A useful memory tip: “tmpfs is temporary and tiny—check your RAM, not your disk.”
PCD Deploying applications Practice Question
This PCD practice question tests your understanding of deploying applications. 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 company is deploying a batch job that runs once a day on Compute Engine. They are using a startup script to install dependencies and run the job. The job writes output to Cloud Storage. Recently, the job started failing intermittently with "No space left on device" errors, even though the persistent disk has 100 GB free. The team has verified that the disk is not fragmented and that the inode usage is low. The job processes large files and creates many temporary files in /tmp. They suspect the /tmp directory is filling up. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The /tmp partition is using a small temporary disk that is separate from the persistent disk.
Option A is correct because on many Compute Engine images, /tmp is mounted as a tmpfs (in-memory filesystem) which has a limited size, often a fraction of the instance's memory. When the job creates many temporary files, it can fill the tmpfs, causing "No space left on device" even though the persistent disk has ample free space. Option B is incorrect because while cleanup would help, the root cause is limited space in /tmp. Option C is incorrect because insufficient RAM would cause swapping, not a filesystem full error. Option D is incorrect because Cloud Storage quota would produce errors when writing to the bucket, not on the local filesystem.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
The /tmp partition is using a small temporary disk that is separate from the persistent disk.
Why this is correct
Often /tmp is a tmpfs with limited capacity; creating too many temporary files fills it.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The instance's RAM is insufficient, causing swap to fill the disk.
Why it's wrong here
Swap usage would consume persistent disk space, but the error would show on the root partition, not necessarily /tmp.
✗
The startup script is not cleaning up temporary files.
Why it's wrong here
Cleanup would help but does not explain why space runs out despite large persistent disk.
✗
The Cloud Storage bucket quota is exceeded.
Why it's wrong here
This would cause errors when writing to Cloud Storage, not a local 'No space left on device'.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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
Swap usage would consume persistent disk space, but the error would show on the root partition, not necessarily /tmp.
Detailed technical explanation
How to think about this question
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.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which PCD 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.
Deploying applications — This question tests Deploying applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The /tmp partition is using a small temporary disk that is separate from the persistent disk. — Option A is correct because on many Compute Engine images, /tmp is mounted as a tmpfs (in-memory filesystem) which has a limited size, often a fraction of the instance's memory. When the job creates many temporary files, it can fill the tmpfs, causing "No space left on device" even though the persistent disk has ample free space. Option B is incorrect because while cleanup would help, the root cause is limited space in /tmp. Option C is incorrect because insufficient RAM would cause swapping, not a filesystem full error. Option D is incorrect because Cloud Storage quota would produce errors when writing to the bucket, not on the local filesystem.
What should I do if I get this PCD question wrong?
Identify which PCD 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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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