The answer is a high vm.swappiness value, which causes the kernel to prioritize swapping out anonymous pages even when ample free memory is available. In this scenario, with 15 GB of free RAM and 10 GB in buffers/cache, the system should not be consuming 6 GB of swap unless the swappiness parameter is set too high—the default of 60 aggressively moves data to swap to free up memory for file caching, even when that trade-off is unnecessary. On the Linux Foundation Certified System Administrator LFCS exam, this question tests your understanding of memory management and the kernel’s behavior under the vm.swappiness setting; a common trap is assuming swap usage always indicates a memory shortage, when in fact it often points to a misconfigured swappiness value. Remember the mnemonic: “High swappiness swaps sooner; low swappiness stays in RAM longer.”
LFCS Operation of Running Systems Practice Question
This LFCS practice question tests your understanding of operation of running systems. 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 systems administrator is troubleshooting a server that runs a database application. The server has 64 GB of RAM and 16 CPU cores. The administrator notices that the system is using a significant amount of swap space even though there is plenty of free memory. The 'free -m' command shows: total memory = 65536, used = 50000, free = 15536, buffers/cache = 10000, swap total = 8192, swap used = 6000. Which of the following 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 vm.swappiness value is set too high.
Option B is correct because a high vm.swappiness value (default 60) causes the kernel to aggressively swap out anonymous pages even when ample free memory exists. With 15 GB free and 10 GB in buffers/cache, the system should not be using 6 GB of swap unless swappiness is set too high, forcing premature swapping.
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 vm.dirty_ratio and vm.dirty_background_ratio are set too high.
Why it's wrong here
These parameters control how much dirty page cache can accumulate. High values could cause more I/O, but not necessarily swap usage.
✓
The vm.swappiness value is set too high.
Why this is correct
A high swappiness value (e.g., 100) makes the kernel more likely to swap pages out to disk even when there is free memory available.
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 database is configured to use huge pages, which are not swappable.
Why it's wrong here
Huge pages are not swappable, so they would reduce swap usage, not increase it.
✗
The vm.vfs_cache_pressure is set too low.
Why it's wrong here
A low vfs_cache_pressure causes the kernel to retain filesystem cache, which would use memory, not swap. This would decrease swap usage.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Linux Foundation often tests the misconception that swap usage only occurs when memory is full, but the trap here is that vm.swappiness can cause swapping even with abundant free memory, leading candidates to overlook the kernel's proactive swapping behavior.
Detailed technical explanation
How to think about this question
vm.swappiness (range 0–100) biases the kernel's page reclaim algorithm: a high value prefers swapping out anonymous pages over reclaiming file-backed page cache. Even with free memory, the kernel may swap if swappiness is high, because it tries to keep more file cache available. In real-world scenarios, databases often benefit from low swappiness (e.g., 10) to avoid latency spikes from swap I/O.
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.
TExam Day Tips
→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 practitioner preparing for the LFCS 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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Operation of Running Systems — This question tests Operation of Running Systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The vm.swappiness value is set too high. — Option B is correct because a high vm.swappiness value (default 60) causes the kernel to aggressively swap out anonymous pages even when ample free memory exists. With 15 GB free and 10 GB in buffers/cache, the system should not be using 6 GB of swap unless swappiness is set too high, forcing premature swapping.
What should I do if I get this LFCS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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