This LFCS practice question tests your understanding of essential commands. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 system administrator monitors a server that periodically becomes unresponsive for a few seconds. Investigation reveals that the kernel OOM killer is being invoked, but standard memory usage monitoring tools like 'free' and 'top' show less than 50% memory usage. The server runs a web server and a database. Which of the following is the most likely cause and diagnostic step?
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 kernel is using a large amount of memory for slab caches. Use 'slabtop' to examine kernel memory allocations.
Option D is correct because the kernel OOM killer can be triggered by high slab cache usage, which is memory allocated for kernel data structures like inode and dentry caches. Standard tools like 'free' and 'top' may show low overall memory usage because they report only user-space memory, while slab caches are accounted separately. Using 'slabtop' allows the administrator to identify which kernel slab caches are consuming excessive memory, often due to a large number of small files or heavy filesystem metadata operations.
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 server is experiencing a fork bomb. Use 'ps -ef | wc -l' to count processes.
Why it's wrong here
A fork bomb would cause high process count and load, not specifically OOM.
✗
The database is using swap space excessively. Use 'swapon -s' to check swap usage.
Why it's wrong here
Swap usage is a symptom of memory pressure, not the cause of OOM.
✗
The web server is leaking file descriptors. Use 'lsof -n' to check open files.
Why it's wrong here
File descriptor leaks cause 'too many open files', not OOM.
✓
The kernel is using a large amount of memory for slab caches. Use 'slabtop' to examine kernel memory allocations.
Why this is correct
Slab caches can consume significant memory not shown in standard memory tools; 'slabtop' helps identify this.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume OOM kills are always due to user-space memory exhaustion, overlooking that kernel slab caches can consume significant memory and trigger the OOM killer even when 'free' and 'top' show low usage.
Detailed technical explanation
How to think about this question
The kernel slab allocator manages memory for small objects like inodes, dentries, and buffer heads; a high number of files or directories can cause the dentry and inode caches to grow significantly, consuming memory that is not shown by user-space tools. The OOM killer is invoked when the kernel's memory management determines that the system is critically low on free memory, which can happen even if user-space memory usage appears low, because slab memory is part of the kernel's own memory consumption. In real-world scenarios, a web server serving many static files or a database with many open tables can inflate slab caches, leading to OOM kills that are puzzling without examining /proc/slabinfo or using slabtop.
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.
Essential Commands — This question tests Essential Commands — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The kernel is using a large amount of memory for slab caches. Use 'slabtop' to examine kernel memory allocations. — Option D is correct because the kernel OOM killer can be triggered by high slab cache usage, which is memory allocated for kernel data structures like inode and dentry caches. Standard tools like 'free' and 'top' may show low overall memory usage because they report only user-space memory, while slab caches are accounted separately. Using 'slabtop' allows the administrator to identify which kernel slab caches are consuming excessive memory, often due to a large number of small files or heavy filesystem metadata operations.
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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