This LFCS practice question tests your understanding of essential commands. 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.
Which THREE commands can change the priority of an already running process?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
top (press 'r')
Option B is correct because the `top` interactive command allows you to change the priority (nice value) of a running process by pressing 'r' and entering the PID and new nice value. This directly modifies the process's scheduling priority without restarting it.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 -STOP
Why it's wrong here
kill -STOP suspends execution, it does not alter priority.
✓
top (press 'r')
Why this is correct
top's interactive 'r' command allows changing the nice value of a running process.
Related concept
Read the scenario before looking for a memorised answer.
✓
chrt
Why this is correct
chrt sets or retrieves the real-time scheduling attributes, which effectively changes priority.
Related concept
Read the scenario before looking for a memorised answer.
✗
nice
Why it's wrong here
nice launches a new process with a specified priority, it does not affect running processes.
✓
renice
Why this is correct
renice changes the priority of an existing process by PID or process group.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse `nice` (which only sets priority for new processes) with `renice` (which modifies running processes), or mistakenly think `kill -STOP` changes priority when it actually halts the process.
Detailed technical explanation
How to think about this question
The `renice` command alters the scheduling priority of an existing process by adjusting its 'nice' value, which ranges from -20 (highest priority) to 19 (lowest priority) on Linux. The `chrt` command sets real-time scheduling policies (e.g., SCHED_FIFO, SCHED_RR) and priorities, which are separate from the nice value and affect processes differently under the CFS scheduler. In real-world scenarios, using `renice` is common for lowering the priority of CPU-intensive background tasks to maintain system responsiveness.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Essential Commands — This question tests Essential Commands — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: top (press 'r') — Option B is correct because the `top` interactive command allows you to change the priority (nice value) of a running process by pressing 'r' and entering the PID and new nice value. This directly modifies the process's scheduling priority without restarting it.
What should I do if I get this LFCS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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