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 process (PID 1234) is hung and cannot be killed with SIGTERM. To force termination, which signal should be sent?
kill -9 1234 (SIGKILL)
SIGKILL cannot be caught and kills immediately.
kill -15 1234 (SIGTERM)
Why wrong: SIGTERM is the default and can be caught.
kill -2 1234 (SIGINT)
Why wrong: SIGINT is also catchable.
kill -1 1234 (SIGHUP)
Why wrong: SIGHUP can be caught and handled.
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 (SIGKILL)
SIGKILL (signal 9) is the correct choice because it cannot be caught, blocked, or ignored by the process. Unlike SIGTERM, which allows the process to perform cleanup, SIGKILL immediately terminates the process at the kernel level, making it the only reliable way to force-kill a hung process that ignores other signals.
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 1234 (SIGKILL)
Why this is correct
SIGKILL cannot be caught and kills immediately.
Related concept
Read the scenario before looking for a memorised answer.
kill -15 1234 (SIGTERM)
Why it's wrong here
SIGTERM is the default and can be caught.
kill -2 1234 (SIGINT)
Why it's wrong here
SIGINT is also catchable.
kill -1 1234 (SIGHUP)
Why it's wrong here
SIGHUP can be caught and handled.
Common exam traps
The trap here is that candidates often confuse SIGTERM (15) as a 'force kill' signal, not realizing that a hung process can ignore it, while SIGKILL (9) is the only signal that guarantees termination.
Detailed technical explanation
Under the hood, SIGKILL (9) bypasses the process's signal handlers entirely and is delivered directly to the kernel's task management, which immediately removes the process from the run queue and frees its resources. A real-world scenario is a zombie or D-state process (uninterruptible sleep) where even SIGKILL may fail; in such cases, a system reboot or kernel intervention is required. Note that SIGKILL cannot be sent to PID 1 (init/systemd) as a safety measure.
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 1234 (SIGKILL) — SIGKILL (signal 9) is the correct choice because it cannot be caught, blocked, or ignored by the process. Unlike SIGTERM, which allows the process to perform cleanup, SIGKILL immediately terminates the process at the kernel level, making it the only reliable way to force-kill a hung process that ignores other signals.
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: 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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