LFCS Operation of Running Systems Practice Question
Which THREE commands can display the current CPU utilization statistics on a Linux system?
⚠ Common exam trap
A common mix-up: candidates confuse `free` or `uptime` with CPU monitoring tools, but `free` is strictly memory-focused and `uptime` only shows load averages, not actual CPU utilization percentages.
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
✓
top
Option B, top, is correct because it is an interactive process viewer that continuously reports CPU utilization statistics, including per-core and aggregate usage, load average, and per-process CPU consumption. Option C, sar -u, is correct because the -u flag of the sar command from the sysstat package reports CPU utilization statistics (user, system, iowait, idle percentages) either for the current day or a specified interval. Option D, mpstat -P ALL, is correct because mpstat from the sysstat package with -P ALL displays per-processor CPU utilization statistics, showing each individual CPU core's usage percentages. Option A, free, is incorrect because it only reports memory and swap usage, not CPU statistics. Option E, uptime, is incorrect because it only shows the current time, system uptime, number of logged-in users, and load averages, without detailed CPU utilization percentages.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
free
Why it's wrong here
free reports memory and swap usage from /proc/meminfo; it exposes no CPU time counters at all. It would be correct for a question about available RAM. CPU utilisation requires reading /proc/stat via top, mpstat, vmstat or sar, which compute busy versus idle jiffies.
- ✓
top
Why this is correct
`top` provides a live, continuously refreshing view of per-process and aggregate CPU utilisation, satisfying the requirement to display current statistics. Its interactive display reads directly from `/proc`, showing user, system, nice, idle and wait percentages. Unlike `uptime`, which reports only load averages, `top` gives instantaneous utilisation figures.
- ✓
sar -u
Why this is correct
`sar -u` reports CPU utilisation from the system activity recorder, reading historical samples collected by `sadc` rather than a live snapshot. This satisfies the stem's requirement to display current CPU utilisation statistics, since the most recent interval reflects present activity, and it also exposes user, system, idle and iowait percentages.
- ✓
mpstat -P ALL
Why this is correct
`mpstat -P ALL` reports per-processor CPU statistics, satisfying the requirement to display current CPU utilisation. Unlike `top`, which refreshes interactively, it prints a single snapshot of user, system, idle and iowait percentages for every core, drawn from `/proc/stat`. This makes it a valid non-interactive command for the scenario.
- ✗
uptime
Why it's wrong here
uptime reports load averages over 1, 5 and 15 minutes, plus how long the system has run — not instantaneous CPU utilisation percentages. It would suit availability or load-trend questions. Commands reading /proc/stat, such as top, mpstat or vmstat, give the per-CPU utilisation figures the question asks for.
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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.