In the previous article I described how my 2015 MacBook felt worse after an upgrade that was supposed to make it faster, and how a load average of ~80 with every process at 0.0% CPU led me to suspect the disk instead of Spotlight. This article is the technical part: the exact commands, in the right order, and what each result means.

Step 1 — Check whether it's Spotlight

mdutil -s /

This command shows Spotlight's indexing status on the main volume. The output says "Indexing enabled" or "Indexing disabled". If it's reindexing after a system upgrade or a disk change, it's normal for it to use resources for a while. The important thing is not to stop here: turning Spotlight off with mdutil -i off / may relieve the symptom, but if the problem persists afterwards, you're treating the symptom, not the root cause.

Step 2 — Look at the system's overall health

top -l 1 | head -8

This gives a snapshot of the system's state, including the load average — three numbers representing the average load over the last 1, 5 and 15 minutes. It's important to understand what it really measures: it isn't the percentage of CPU in use, it's how many processes are waiting their turn for the CPU or the disk. A sustained load average of 70–80 on an 8GB Mac doesn't mean "it's busy doing a lot" — it means there's a queue of processes waiting on a saturated resource.

Step 3 — Identify the culprit process (or rule out that there is one)

top -o cpu -l 1 -n 12
top -o mem -l 1 -n 12

These commands sort active processes by CPU and by memory usage respectively, showing the top 12. If a specific app is hogging the system, it will show up at the top with a high percentage and the investigation ends there — close it or reinstall it.

The key twist in the real case was this: every process showed 0.0% individual CPU. None of them, not even added together, explained a load average of 80. That contradiction — high load with no CPU culprit — is the sign that the bottleneck is disk I/O: reads and writes that never quite finish, without any single process "taking the blame" in the CPU metrics.

"When no single process explains the problem, stop staring at the process list and start looking at the disk. That change of focus is what solves the diagnosis."

Step 4 — Check the disk's physical health

diskutil verifyVolume /
diskutil info / | grep -i "smart\|protocol"

The first command checks the volume's integrity and reports file-system errors, if any. The second shows the SMART status — the physical health self-diagnosis the disk itself reports. If it says "Verified", the disk is healthy and the problem is probably configuration or software. If not, no formatting, reinstall or cache cleaning will fix a hardware problem.

This is the check to run before reinstalling macOS from scratch, not after. Reinstalling on a disk with physical faults only postpones the same problem by a few weeks.

What I learned from the order of these steps

The value of this flow isn't in the commands themselves — they're documented in any macOS manual — but in the order: first rule out the most common and visible cause (Spotlight), confirm with an objective number (load average), isolate whether there's a specific culprit (CPU/memory per process) and, if there isn't, check the hardware before touching the software. Skipping this order is why so many "slow Mac" diagnoses end in a reinstall that fixes nothing.

This article is part of a series: see also Chrome vs Safari on an old Mac and how to decide whether to optimize or replace your Mac.

Frequently asked questions

Which command shows whether Spotlight is reindexing on macOS?

The command 'mdutil -s /' shows whether Spotlight indexing is enabled or disabled on the main volume. If it says 'Indexing enabled' and the Mac is slow, it may be reindexing — but turning it off only treats the symptom, it doesn't confirm the root cause.

How do I see my Mac's load average from Terminal?

Running 'top -l 1 | head -8' gives a snapshot of the system, including the load average. That number represents how many processes are waiting their turn for the CPU or the disk — it isn't the same as the percentage of CPU in use.

How do I know whether my Mac's problem is a specific process or the disk?

Sort the processes with 'top -o cpu -l 1 -n 12': if none shows high individual CPU usage but the system is still slow, the cause is almost always constant disk I/O, not a specific app.

What is SMART status and why check it before reinstalling macOS?

SMART status is the disk's physical-health self-diagnosis. Check it with 'diskutil info / | grep -i smart'. If it says 'Verified' the disk is healthy; if not, no formatting or software reinstall will fix a hardware problem. It's the check to do before reinstalling, not after.