How to check your Mac: Disk Utility First Aid, Apple Diagnostics and safe mode

If we sent you this link: these are the steps we would otherwise type out in an email. Go through them in order, take your time, and stop at any step that does not look like the description. None of these checks asks you to delete anything, and where a button would wipe something, we say so.

A Mac that has gone slow, freezes or will not start properly is often blamed on the internet, and often it is the Mac. Apple builds three checks into every Mac: First Aid in Disk Utility checks the disk, Apple Diagnostics tests the hardware, and safe mode shows whether some software is to blame. Each one is explained below, with the exact keys for your kind of Mac. If you would rather someone sat beside you, book home tech support to go through these checks with you.

If you are not yet sure it is the Mac at all, start with sorting a computer problem from an internet problem, which takes two minutes. For a Windows PC, the Windows checks, SFC, DISM and CHKDSK are the same idea in a different place.

Do I have an Apple silicon Mac or an Intel Mac?

Click the Apple menu in the top left corner of the screen and choose About This Mac. If the window shows a line labelled Chip, your Mac has Apple silicon. If it shows a line labelled Processor with an Intel name, it is an Intel Mac.

It matters because the keys you hold down at start-up are different. Here they are side by side, and each one is explained further down.

The start-up keys for each kind of Mac

To do this	Mac with Apple silicon	Intel Mac
Start up from macOS Recovery	Hold the power button until you see Loading start-up options, let go, then click Options and Continue	Press and release the power button, then hold Command (⌘) and R
Run Apple Diagnostics	Hold the power button until you see Options, let go, then hold Command (⌘) and D	Hold the D key as it starts
Start in safe mode	Hold the power button until Loading start-up options appears, then hold Shift and click Continue in Safe Mode	Hold Shift as it starts
Reset NVRAM	Not needed, Apple says	Hold Option, Command, P and R for about 20 seconds

On a MacBook with Touch ID, the Touch ID button is the power button.

Why should I back up my Mac first?

Because Apple says to, before any repair: “Make sure you have a current backup of your data”, in case Disk Utility finds damaged files or errors it cannot fix. A backup costs you an external drive and some time. Losing ten years of photos costs a great deal more.

The backup tool built into every Mac is Time Machine. It needs an external drive, ideally with at least twice the storage of your Mac.

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These steps are for macOS Ventura and later, which have System Settings. On an older Mac, Apple’s guide to backing up with Time Machine (opens in a new tab) links to the steps for your version.

1. 1

   Plug the external drive into the Mac

   Connect it to the right port on your Mac, a USB or Thunderbolt port, with the drive's own cable.

2. 2

   Open Time Machine settings

   From the Apple menu, choose System Settings. Click General in the sidebar, then click Time Machine on the right.

3. 3

   Add the drive

   Click Add Backup Disk, or the + button. Select your drive and click Set Up Disk.

4. 4

   Let the first backup run

   The Mac starts backing up straight away. The first backup can take longer than you expect, and you can keep using the Mac while it runs.

5. 5

   Back up again before any check

   Next time, choose Back Up Now from the Time Machine menu in the menu bar at the top of the screen.

If the photos started on an iPhone, getting them off the phone and onto the Mac first is the step before Time Machine.

How do I run First Aid in Disk Utility?

Start the Mac up from macOS Recovery, open Disk Utility, and run First Aid on each item in the sidebar from the bottom up: the volumes, then the container, then the disk itself. Apple says to use Recovery when you are checking the startup disk, which is the disk inside your Mac and the one most people need to check.

If you are only checking an external drive, you do not need Recovery: open Finder, click Applications, open the Utilities folder and double-click Disk Utility, then go straight to step 3.

1. 1

   Start up from macOS Recovery

   Shut the Mac down. On a Mac with Apple silicon, press and hold the power button until you see Loading start-up options, let go, then click Options, then Continue. On an Intel Mac, press and release the power button, then straight away hold Command (⌘) and R until you see an Apple logo or a spinning globe. If asked, choose a Wi-Fi network, your startup disk (such as Macintosh HD), then a user and that user's password.

2. 2

   Open Disk Utility

   A window of utilities appears. Select Disk Utility, then click Continue. Leave Restore from Time Machine and Reinstall macOS alone.

3. 3

   Show every item

   From the menu bar or the toolbar, choose View, then Show All Devices, if it is there. The sidebar lists each disk, starting with the startup disk, and under each one its container and volumes.

4. 4

   Start at the bottom

   Select the last volume listed under the disk. Click First Aid, then Run (or Repair Disk, if that is what yours says). If asked for a password to unlock the disk, type the one you use to log in to the Mac.

5. 5

   Click Done, and move up one

   When it finishes, click Done. Select the next item up and run First Aid again. If the button is dimmed, skip that item.

6. 6

   Work up to the disk

   Do each volume, then the container, then the disk at the top. If you see Macintosh HD and Macintosh HD - Data, do both: Apple says to check the data volume as well.

7. 7

   Restart

   When you have finished, choose Restart from the Apple menu.

Apple does not give a time for First Aid, so let each item finish and click Done before you move on.

Pick a step to watch

Show All Devices Volumes first Then the container Then the disk

First Aid

View > Show All Devices

• Storage device
• Container
• Macintosh HD
• Macintosh HD - Data

First Aid

• Storage device
• Container
• Macintosh HD
• Macintosh HD - Data

Run Done

Run Done

First Aid

• Storage device
• Container
• Macintosh HD
• Macintosh HD - Data

Run Done

First Aid

• Storage device
• Container
• Macintosh HD
• Macintosh HD - Data

Run Done

Show All Devices

Choose View, then Show All Devices. The sidebar now lists the disk, its container and its volumes.

Volumes first

Start with the last volume in the list. Click First Aid, then Run, and Done when it finishes. Then the volume above it.

Then the container

Next, select the container and run First Aid on it the same way.

Then the disk

Last, the disk itself. If Disk Utility reports that the disk appears to be OK or has been repaired, you're done.

What do the First Aid results mean?

If Disk Utility reports that the disk appears to be OK or has been repaired, you are done. Anything else needs one more step, and the table says which. Click Show Details in the First Aid window if you want to see what it checked.

First Aid results, and what to do next

What Disk Utility says	What it means	What to do
The disk appears to be OK, or has been repaired	First Aid found nothing wrong, or fixed it	Nothing. Move on to the next item, or restart
Overlapped extent allocation	Two or more files use the same space on the disk, and at least one is probably damaged	Check each file it lists. Most have an alias in a DamagedFiles folder at the top of the disk. Get help before you delete anything
The First Aid process failed	It could not finish the repair	Run First Aid on that item once more
The disk is about to fail	The disk itself is wearing out and cannot be repaired	Back up straight away. The disk needs replacing
Errors it cannot repair	The repair has gone as far as it can	Stop here, and make sure your backup is current

If the disk does not appear in the sidebar at all, shut the Mac down, unplug everything that is not needed, and try again. For an external drive, check its cable, its connection and its power. If it still does not appear, Apple says the Mac or the drive may need service.

How do I run Apple Diagnostics?

Unplug the extras, shut the Mac down, then start it with the diagnostics keys for your kind of Mac. Apple Diagnostics tests the hardware itself, such as the memory, the storage and the fans, and finishes with a reference code. Run it when you think the hardware may be at fault: the Mac freezes, crashes or turns itself off.

First, get the Mac ready:

• Unplug the extras. Leave only the keyboard, the mouse, the display, a network cable if you use one, and the power.
• Put it on a hard, flat, steady surface with room for air to move around it.
• Shut it down. If it will not shut down, hold the power button for up to 10 seconds.

Then start the test:

1. 1

   On a Mac with Apple silicon

   Press and hold the power button. Keep holding it while the Mac turns on and loads the start-up options. When you see Options, let go. Then press and hold Command (⌘) and D until the Mac restarts.

2. 2

   On an Intel Mac

   Turn the Mac on, and straight away press and hold the D key. Let go when you see a progress bar or you are asked to choose a language. If D does not work, start again holding Option (⌥) and D.

3. 3

   Follow what the screen says

   You may be asked to join a Wi-Fi network. If you are offered Run Offline, click it, unless Apple or a repair technician has started a session for your Mac. On macOS Tahoe 26 and later you choose which test to run.

When testing is complete, Apple Diagnostics shows the results. Write down the reference code, or take a photo of the screen. Apple’s list of Apple Diagnostics reference codes (opens in a new tab) explains each one:

Some Apple Diagnostics reference codes

Code	What Apple says	What to do
ADP000	No issues found	The hardware tested fine. Try safe mode next
NDD001	There may be an issue with the USB hardware	Unplug everything but the keyboard, mouse and network adapter, and run the test again
PPM001 to PPM016	There may be an issue with a memory module, or with the onboard memory	Contact Apple, or take the Mac to an Apple Store or an Apple Authorised Service Provider
VDH001 to VDH004	There may be an issue with a storage device	Back up first if the Mac still starts, then contact Apple or an Apple Store
PPF001, PPF003, PPF004	There may be an issue with the fan	Contact Apple, or take the Mac to an Apple Store

Apple’s own page on how to use Apple Diagnostics (opens in a new tab) has the full steps.

How do I start my Mac in safe mode?

Start it with the Shift key held. Safe mode stops some software loading when the Mac starts, such as login items and extras macOS does not need, runs a basic check of the startup disk, and clears some system caches. If the problem goes away in safe mode, the hardware is probably fine and something that loads at start-up is the cause.

1. 1

   On a Mac with Apple silicon

   Shut the Mac down. Press and hold the power button until you see Loading start-up options, then let go. Select your startup disk, usually called Macintosh HD. Press and hold Shift, then click Continue in Safe Mode. Log in, and if asked, log in again.

2. 2

   On an Intel Mac

   Turn the Mac on or restart it, and straight away press and hold Shift. Let go when the login window appears. You may be asked to log in twice.

3. 3

   Check it worked

   The login window may show Safe Boot in red in its top right corner. Or hold Option, choose System Information from the Apple menu, click Software, and look for Boot Mode: Safe.

4. 4

   Use the Mac for a while

   Do whatever usually goes wrong. Some things may not work as normal in safe mode, such as Wi-Fi, sound, video and some plugged-in devices, so judge it on the problem you came for.

5. 5

   Leave safe mode

   Restart the Mac normally from the Apple menu.

If the problem does not come back after a normal restart, Apple says the checks safe mode ran may have fixed it. If it comes back, something that starts with the Mac is the likely cause, such as a login item or a program you installed, and that is worth having someone look at.

Should I reset NVRAM on my Mac?

Only on an Intel Mac, and only when a setting keeps going wrong. NVRAM holds a few settings: the sound volume, the display resolution, the startup disk and the time zone. Apple says the reset does not apply to Macs with Apple silicon and is not needed on them, so if your Mac shows Chip in About This Mac, skip this.

On an Intel Mac:

1. 1

   Shut down your Mac.

2. 2

   Turn it on, and straight away press and hold these four keys together: Option, Command, P and R.

3. 3

   Let go after about 20 seconds. The Mac may seem to restart while you hold them.

4. 4

   When it has started up, check your sound, display and time zone, and set any that have changed.

Do I need Terminal to check my Mac?

No. First Aid in Disk Utility is the check Apple documents for the disk, and you do not need to type anything. Terminal is the Mac’s window for typed commands, and Apple does not give a Terminal command for this check, so this page does not give one either.

If someone has asked you to open Terminal, it is in the same place as Disk Utility: open Finder, click Applications, open the Utilities folder and double-click Terminal. To close it, choose Terminal, then Quit Terminal, from the menu bar.

Is my Mac running slow, or is it the internet?

If websites are slow but the Mac opens its own programs and files quickly, the internet is the likelier cause. Try the same website on a phone on the same WiFi: if the phone is slow too, it is the connection, and why your NBN is slow is the place to start. If the Mac says it is on the WiFi but nothing loads, connected to WiFi with no internet goes through it.

If the Mac is slow even with nothing open online, the checks on this page are the right ones, and our two-minute sort, computer or connection covers the other signs: heat, fans, a full disk and updates waiting.

When to stop and call us, and when not to

You do not need us when First Aid says the disk appears to be OK, Apple Diagnostics shows ADP000 and the problem has gone, or safe mode and a normal restart sorted it. Keep your Time Machine backup running and you are in good shape.

Stop and get help when First Aid says it cannot repair the disk, the disk is about to fail, Apple Diagnostics shows a hardware code, or the same freeze keeps coming back. A hardware code is a repair for Apple, an Apple Store or an Apple Authorised Service Provider: we set up and help, and we do not repair hardware, fit parts or recover files from a disk that has failed. What our home tech support does is the rest of it: run these checks with you, set up the backup so it keeps running, clean up what loads at start-up, and set up a new Mac and move your photos and files across if it comes to that.

If the Mac checks out and the internet is still the problem, that is an internet technician to test the connection, or a WiFi technician if only the WiFi is weak.

Not sure which it is? Send us a message with what the screen says, or ring 02 9188 1577.