Monitor Your Mac’s Health
No matter how diligently you perform the maintenance tasks in this book, you won’t truly know how well (or how poorly) your Mac is running unless you make the effort to find out. The fact that no smoke is billowing from your Mac is a good sign, of course, but it’s hardly definitive proof that all is well. In this chapter, I show you how to find out what’s going on under the hood.
Use Monitoring Utilities
Numerous utilities (most of them free) can provide up-to-the-minute statistics about your Mac. In most cases, these apps run in the background all the time, but if you prefer, you can run them manually when you get curious about your Mac’s current state. I provide a list of several such utilities just ahead (in Monitoring Utilities). But first, you should understand what data you might want to monitor and why.
RAM Usage
For the most part, macOS manages your computer’s RAM efficiently. Apps can dynamically adjust the amount of memory they use, and even if all your RAM is actively in use, a virtual memory system lets macOS use a portion of your disk (or SSD) to extend your RAM, automatically swapping (or “paging”) data between the disk and the physical RAM as needed. Even so, if you have enough apps open at once, and if they require enough memory to perform their respective tasks, you can reach a point where data swapping occurs constantly. This uses disk space and slows everything way down.
You should also be aware of a type of bug known as a memory leak. Apps usually ask the system for a certain amount of memory for any given task and then return it when they’re done. Sometimes, due to a programming error, an app keeps taking memory and not returning any, so that by doing nothing more than staying open, it chews up more and more RAM. You can recover the used memory by quitting the app—but you might not even know you have this problem without monitoring your RAM usage.
For all these reasons, I suggest keeping an eye on how much RAM is currently in use. If the free RAM drops near zero, consider closing windows, quitting apps, or even restarting your Mac to reduce your dependence on virtual memory. Better yet, add more RAM (if possible); read the sidebar Be Sure You Have Enough RAM.
Disk Usage
Thanks to the combination of rising disk capacity, Optimized Storage (and similar features), and low-level improvements in macOS, you’re now less likely to run out of space than you were a few years ago. But, as I explained in Clean Out Accumulated Cruft, the consequences of running out of space can be severe. For one thing, as a hard disk approaches its maximum capacity, fragmentation can make your Mac run more slowly (see Defragment Your Hard Disk). Worse, you could lose data because your Mac has no space to save a file. Even more seriously, your Mac may hang, crash, or fail to start up if it runs out of physical RAM and runs out of disk space for virtual memory.
How much disk space should you leave available for file storage, virtual memory, system overhead, and other tasks? As I said earlier (in Clean Out Accumulated Cruft), my rule of thumb is that the minimum amount of space you should leave unused on your drive is 6 GB or twice the amount of RAM installed, whichever is larger—with some qualifications for those with truly immense amounts of RAM. When your disk gets close to that level, delete unneeded files, and archive seldom-used files to external storage.
Although you can tell how much available space is on a disk by selecting it in the Finder and choosing File > Get Info, you may not notice if it gets dangerously full while you’re working. (macOS does show a warning when space gets critically low, but it appears too late for my taste.) Several utilities can display a live indicator of your disks’ available space.
CPU Load
Your Mac contains one or more CPUs—chips that do the bulk of the computer’s information processing. Depending on what software is running and what that software is doing, the CPU load goes up and down. Because all your apps share the available CPU power, it’s generally true that the higher the overall load, the slower your software will run. Greater CPU load also means higher heat, making your computer’s fans work harder (I discuss temperatures next).
Having your CPU(s) run at 100% capacity from time to time is normal. However, if the load is always at or near maximum—or if it’s high even when your computer is relatively inactive—you may have a problem. For example, a background app could have a bug that causes it to use too much processor capacity, slowing down your foreground tasks. Or you may be running more apps than your hardware can handle gracefully. In any case, keeping an eye on CPU usage can help you spot potential problems before they get out of hand. Some CPU monitoring tools show usage by app, so if one app is hogging too much CPU capacity, you can force it to quit.
Temperatures
Extreme heat can damage delicate components inside your Mac. This is why all Macs have cooling systems, most of which rely on one or more fans to vent heat away from the processor, hard drive, and other vital components. (The MacBook (Retina, 2015 or later) uses a passive, fanless cooling system.) These fans, in turn, rely on one or more internal temperature sensors that tell them when to turn on or off or to increase or decrease speed. If a fan malfunctions, if dust blocks the flow of air through your Mac (see De-Dust Your Mac), or if a defect in your Mac causes it to overheat, bad things can happen. Your Mac may hang, shut down unexpectedly, or display other improper behavior. You might be looking at an intermittent inconvenience or an expensive repair. In any case, it behooves you to be alert to excessive temperatures.
Several utilities monitor each of your computer’s internal temperature sensors, so that you can easily see when heat exceeds safe limits and take action before damage occurs.
Other Statistics
Some utilities monitor other statistics that may be interesting (though not necessarily relevant to your Mac’s health). These include:
Network traffic
Disk access activity
Battery level (for portables)
System uptime (time since the Mac was last turned on or restarted)
Monitoring Utilities
Here’s a small sampling of the many monitoring utilities for macOS:
Activity Monitor: This utility, included with macOS (located in
/Applications/Utilities) displays CPU load, RAM usage, disk activity and usage, and network traffic (Figure 14).
Figure 14: Activity Monitor displays CPU and RAM usage, among many other statistics. Activity Monitor also displays memory and CPU usage statistics for each running app and enables you to quit individual apps. Although it includes an optional floating CPU window, Activity Monitor is not the best choice for background operation.
Checkmate: From Micromat (makers of TechTool Pro), this utility checks your RAM, battery, disk directory and file structures, and a variety of other system attributes, alerting you when critical problems appear.
FreeSpace: Sitting unobtrusively in your menu bar, this app displays the amount of free space on your startup volume (in red if it’s getting low). Its menu shows the free space on every connected volume, and even lets you eject any mounted volume.
iStat Menus: This versatile, attractive, and highly configurable utility can display detailed information in your menu bar about CPU, RAM, network, and disk usage, temperatures, and more. It can also graph your activity and alert you when parameters go beyond figures you specify.
MenuMeters: My favorite of the group, MenuMeters adds tiny, customizable indicators to your menu bar to display any or all of the following: CPU load, RAM usage, disk access activity (with usage on a drop-down menu), and network traffic (Figure 15). (Although the original author hasn’t updated MenuMeters to work on El Capitan and later, the link above points to an adaptation by Yuji Tachikawa that does.)
Figure 15: MenuMeters can display RAM, CPU usage, and numerous other bits of information, in highly configurable menus. XRG: XRG provides highly customizable graphs of CPU usage, RAM usage, disk access activity, network traffic, up to three internal heat sensors, and battery level, plus the weather (in a city of your choice) and even stock market data.
Check Your Drive’s S.M.A.R.T. Status
Most modern hard drives and SSDs have built-in sensors and monitoring circuitry that form a system called S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology). The idea of S.M.A.R.T. is to detect the warning signs of potential problems before they occur. Although S.M.A.R.T. cannot detect every possible drive problem, it can provide one very valuable warning: “Your drive is about to have problems, so back it up and repair (or replace) it now!”
To check your drive’s S.M.A.R.T. status, open Disk Utility (you can find it in /Applications/Utilities) and select a drive in the list on the left. (In High Sierra or later, if only the volumes are visible and not the drive itself, choose View > Show All Devices.) Then:
If the selected drive supports S.M.A.R.T., you should see this at the bottom of the window: “S.M.A.R.T. Status: Verified” (Figure 16).
Figure 16: Disk Utility shows a drive’s S.M.A.R.T. status. If you see “About to Fail” or “Failing,” back up the drive immediately. You can then use Disk Utility (or a third-party utility) to attempt to repair the drive, but more often than not, “About to Fail” or “Failing” indicates an imminent hardware failure that you cannot fix with software. Even if Disk Utility does appear to solve the problem, don’t trust the drive with important data; replace it as soon as possible.
If your Mac has a Fusion drive, or if you’ve enabled FileVault, then depending on your version of macOS, Disk Utility may not show the S.M.A.R.T. status even if the hardware itself supports S.M.A.R.T. Instead, open System Information (in /Applications/Utilities) and select Storage in the list on the left. If a list of volumes appears at the top, select the one you want to know about and look for S.M.A.R.T. Status in the display on the right (Figure 17).
To get a constant, real-time report of your drive’s S.M.A.R.T. status, you can install a utility such as these (some of which offer other monitoring features too):