LFCS Operation of Running Systems Practice Question
A process (PID 1234) is hung and cannot be killed with SIGTERM. To force termination, which signal should be sent?
⚠ Common exam trap
A common mix-up: candidates 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.
Answer choices
Why each option matters
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.
Answer analysis
Option-by-option breakdown
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 (signal 9) cannot be caught, blocked or ignored by the process, so the kernel terminates it immediately without waiting for handler cleanup. SIGTERM is catchable, which is why the hung process survived the earlier attempt.
- ✗
kill -15 1234 (SIGTERM)
Why it's wrong here
SIGTERM is the polite termination request the stem states has already failed, so resending it changes nothing. It tempts because it is the default signal for the kill command, but SIGKILL (signal 9) cannot be caught or ignored and forces termination.
- ✗
kill -2 1234 (SIGINT)
Why it's wrong here
SIGINT is the terminal interrupt, equivalent to Ctrl+C, and a hung process ignoring SIGTERM will also ignore it. It tempts because it does terminate interactive foreground jobs, but SIGKILL (signal 9) is the uncatchable signal that forces termination.
- ✗
kill -1 1234 (SIGHUP)
Why it's wrong here
SIGHUP is delivered when a controlling terminal closes and is commonly caught or ignored by daemons, so a hung process will not necessarily die. It tempts because it restarts many services, but SIGKILL (signal 9) is the uncatchable signal required here.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.