This LFCS practice question tests your understanding of essential commands. 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.
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1234 99.5 0.2 12345 6789 pts/0 R 10:00 45:00 process_hog
Refer to the exhibit. The output of 'ps aux' shows a process named 'process_hog' with PID 1234 consuming 99.5% CPU. The process is stuck in an infinite loop and does not respond to SIGTERM. Which signal should be used to forcefully terminate it?
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1234 99.5 0.2 12345 6789 pts/0 R 10:00 45:00 process_hog
kill -2 1234
Why wrong: SIGINT is for interactive processes and is likely to be ignored as well.
kill -9 1234
SIGKILL is the ultimate signal that forcefully terminates the process.
kill -15 1234
Why wrong: SIGTERM was already tried and ignored; it would not work.
kill -19 1234
Why wrong: SIGSTOP suspends the process; it does not terminate it.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
kill -9 1234
Option B is correct because SIGKILL (signal 9) cannot be caught, blocked, or ignored by a process, making it the only reliable way to terminate a process that is stuck in an infinite loop and unresponsive to SIGTERM. Since the process does not respond to SIGTERM (signal 15), a forceful kill with kill -9 is necessary.
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.
kill -2 1234
Why it's wrong here
SIGINT is for interactive processes and is likely to be ignored as well.
kill -9 1234
Why this is correct
SIGKILL is the ultimate signal that forcefully terminates the process.
Related concept
Read the scenario before looking for a memorised answer.
kill -15 1234
Why it's wrong here
SIGTERM was already tried and ignored; it would not work.
kill -19 1234
Why it's wrong here
SIGSTOP suspends the process; it does not terminate it.
Common exam traps
In LFCS, the key distinction is between termination signals (SIGTERM, SIGKILL) and stop signals (SIGSTOP). SIGTERM allows graceful shutdown, but if ignored, SIGKILL is the only way to force termination. Some candidates incorrectly use SIGSTOP (pause) or confuse SIGTERM with a guaranteed kill.
Detailed technical explanation
Under the hood, signals are delivered by the kernel to the target process; SIGKILL (9) bypasses all signal handlers and immediately terminates the process without cleanup, while SIGTERM (15) allows the process to perform cleanup via a handler. In real-world scenarios, a process stuck in an infinite loop may have blocked SIGTERM or be in an uninterruptible sleep state (D state), but SIGKILL will still work unless the process is in a kernel-level deadlock. The kill command uses the signal number or name; kill -9 is equivalent to kill -SIGKILL.
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
Essential Commands — This question tests Essential Commands — Read the scenario before looking for a memorised answer..
The correct answer is: kill -9 1234 — Option B is correct because SIGKILL (signal 9) cannot be caught, blocked, or ignored by a process, making it the only reliable way to terminate a process that is stuck in an infinite loop and unresponsive to SIGTERM. Since the process does not respond to SIGTERM (signal 15), a forceful kill with kill -9 is necessary.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 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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