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 system administrator notices that a process is consuming 100% CPU and is unresponsive. Which command should be used to immediately stop the process if the PID is 2345?
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.
Clue: "immediately / without restart"
Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
kill -9 2345
SIGKILL immediately terminates the process and cannot be caught.
pkill -9 processname
Why wrong: pkill targets process names, not a specific PID.
systemctl stop processname
Why wrong: systemctl only manages systemd services, not arbitrary processes.
kill -15 2345
Why wrong: SIGTERM is graceful and may not stop a stuck 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
kill -9 2345
Option A is correct because `kill -9 2345` sends the SIGKILL signal (signal 9) to process ID 2345, which immediately terminates the process without allowing it to clean up or ignore the signal. This is the appropriate action for an unresponsive process consuming 100% CPU, as SIGKILL cannot be caught or blocked by the process.
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 -9 2345
Why this is correct
SIGKILL immediately terminates the process and cannot be caught.
Clue confirmation
The clue words "which command", "immediately / without restart" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
pkill -9 processname
Why it's wrong here
pkill targets process names, not a specific PID.
systemctl stop processname
Why it's wrong here
systemctl only manages systemd services, not arbitrary processes.
kill -15 2345
Why it's wrong here
SIGTERM is graceful and may not stop a stuck process.
Common exam traps
The trap here is that candidates may choose `kill -15` (SIGTERM) thinking it is safer, but the question explicitly requires immediate stoppage of an unresponsive process, where only SIGKILL guarantees termination.
Detailed technical explanation
SIGKILL (signal 9) is one of two signals (the other being SIGSTOP) that cannot be caught, blocked, or ignored by a process; the kernel immediately terminates the process and reclaims its resources. In contrast, SIGTERM (signal 15) allows the process to perform cleanup actions via signal handlers, but a process in an infinite loop or deadlock may never reach the handler. The `kill` command sends signals based on PID, while `pkill` and `killall` match by name, which can lead to unintended terminations if multiple processes share a substring.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: kill -9 2345 — Option A is correct because `kill -9 2345` sends the SIGKILL signal (signal 9) to process ID 2345, which immediately terminates the process without allowing it to clean up or ignore the signal. This is the appropriate action for an unresponsive process consuming 100% CPU, as SIGKILL cannot be caught or blocked by the process.
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", "immediately / without restart". 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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