This LFCS practice question tests your understanding of operation of running systems. 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 system administrator notices that a web server process (PID 1234) is consuming excessive CPU. They want to trace its system calls to identify the cause. Which command should be used?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
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.
ltrace -p 1234
Why wrong: Traces library calls, not system calls.
perf record -p 1234
Why wrong: Records performance counters, not system calls.
gdb -p 1234
Why wrong: Debugger, not a system call tracer.
strace -p 1234
Attaches and traces system calls, ideal for this scenario.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
strace -p 1234
The correct command is `strace -p 1234`, which attaches to the running process (PID 1234) and intercepts all system calls (e.g., read, write, open) made by that process. This allows the administrator to see exactly what the web server is doing at the kernel level, such as excessive file I/O or network operations, which can pinpoint the cause of high CPU usage. Other tools like ltrace, perf, or gdb serve different purposes (library calls, profiling, debugging) and do not directly trace system calls.
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.
ltrace -p 1234
Why it's wrong here
Traces library calls, not system calls.
perf record -p 1234
Why it's wrong here
Records performance counters, not system calls.
gdb -p 1234
Why it's wrong here
Debugger, not a system call tracer.
strace -p 1234
Why this is correct
Attaches and traces system calls, ideal for this scenario.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse `strace` (system calls) with `ltrace` (library calls), as both trace function calls but at different layers of the software stack, leading them to pick the wrong tool for kernel-level analysis.
Detailed technical explanation
Under the hood, `strace` uses the `ptrace` system call (specifically `PTRACE_SYSCALL`) to intercept every system call entry and exit, logging arguments and return values. This can generate a massive amount of output for a busy web server, so real-world usage often includes filtering with `-e trace=network` or `-e trace=file` to focus on specific subsystems. A subtle behavior is that `strace` can significantly slow down the traced process (by up to 100x) due to the context-switch overhead of ptrace, which is why it's typically used for short-term diagnosis rather than continuous monitoring.
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
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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: strace -p 1234 — The correct command is `strace -p 1234`, which attaches to the running process (PID 1234) and intercepts all system calls (e.g., read, write, open) made by that process. This allows the administrator to see exactly what the web server is doing at the kernel level, such as excessive file I/O or network operations, which can pinpoint the cause of high CPU usage. Other tools like ltrace, perf, or gdb serve different purposes (library calls, profiling, debugging) and do not directly trace system calls.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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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