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.
After a kernel update, a service fails to start with 'cannot allocate memory'. The system has 16GB RAM and 8GB swap. Which command should the administrator run first to diagnose potential memory limits?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
free -m
Why wrong: Shows system memory, not process limits.
ulimit -a
Shows process resource limits, which may be too low.
cat /proc/meminfo
Why wrong: Shows detailed kernel memory info, but not process limits.
sysctl vm.overcommit_memory
Why wrong: Shows overcommit policy, but not the likely cause for a single process.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
ulimit -a
Option B is correct because `ulimit -a` displays all current user-level resource limits, including `max memory size`, `max processes`, and `max locked memory`. After a kernel update, the service may be hitting a newly enforced or reduced `ulimit` (e.g., `RLIMIT_AS` or `RLIMIT_DATA`), which can cause 'cannot allocate memory' even when system memory is abundant. This command is the fastest way to check if a per-process limit is the culprit.
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.
free -m
Why it's wrong here
Shows system memory, not process limits.
ulimit -a
Why this is correct
Shows process resource limits, which may be too low.
Clue confirmation
The clue words "first", "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
cat /proc/meminfo
Why it's wrong here
Shows detailed kernel memory info, but not process limits.
sysctl vm.overcommit_memory
Why it's wrong here
Shows overcommit policy, but not the likely cause for a single process.
Common exam traps
The trap here is that candidates see 'cannot allocate memory' and immediately think of system memory exhaustion, leading them to choose `free -m` or `/proc/meminfo`, but the LFCS exam tests the distinction between system-wide memory and per-process resource limits enforced by `ulimit`.
Trap categories for this question
Command / output trap
Shows system memory, not process limits.
Detailed technical explanation
The `ulimit` command sets and retrieves per-process resource limits defined by the `setrlimit` system call, which uses `RLIMIT_AS` (address space) and `RLIMIT_DATA` (data segment) to cap virtual memory. A kernel update can alter default PAM configuration files (e.g., `/etc/security/limits.conf` or systemd unit limits via `LimitAS=`) that tighten these values, causing `malloc()` to fail even when system memory is free. In practice, checking `ulimit -a` as the service user (e.g., `sudo -u <service> ulimit -a`) is critical because limits may differ per user or session.
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 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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Operation of Running Systems — This question tests Operation of Running Systems — Read the scenario before looking for a memorised answer..
The correct answer is: ulimit -a — Option B is correct because `ulimit -a` displays all current user-level resource limits, including `max memory size`, `max processes`, and `max locked memory`. After a kernel update, the service may be hitting a newly enforced or reduced `ulimit` (e.g., `RLIMIT_AS` or `RLIMIT_DATA`), which can cause 'cannot allocate memory' even when system memory is abundant. This command is the fastest way to check if a per-process limit is the culprit.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "first", "which command". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.
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