How to run Disk Utility First Aid to check & repair Mac disks?

By Connie | Posted to Home > Howto, updated on September 10th, 2021

Summary: Guide to run Disk Utility First Aid in normal mode and from macOS Recovery mode. It also tells what to do if Disk Utility First Aid fails or is not working on your Mac.

Mac First Aid repairing disk

Disk Utility First Aid is a built-in disk repair software in Mac OS. Its main task is to verify and check the health of the disks and volumes on your Mac, such as the SSD, Macintosh HD, external hard drives, SD cards, etc.

And if necessary, First Aid will repair the detected minor errors related to the formatting and directory structure of the disks or volumes, such as repair corrupted USB flash drive on Mac. That prevents the disk from occurring more seriously corruption.

So, First Aid is a very pragmatic utility on Mac. This post will guide you when and how to use Disk Utility First Aid from the Utilities folder and macOS Recovery mode.

When should you run First Aid on Mac?

If unfortunately, you are running into the following problems, you can run First Aid in Disk Utility as the priority tool to fix them.

  1. Frequent Mac kernel panic.
  2. Mac or apps is frozen.
  3. Mac won't turn on.
  4. Error messages appear to indicate that your drive has some problems.
  5. External devices are not mounting, readable, showing up on Mac.

How to use Disk Utility First Aid from the Utilities folder?

If want to know how to fix corrupted hard drive Mac, you can use First Aid from the Utilities folder in Finder. We'll tell you how to open Disk Utility on Mac and use it to repair disk errors.

Here's how:

  • Open Finder > Applications > the Utilities folder.

Open Utilities in Applications

  • Find Disk Utility and open it.
  • Click View at the upper-left corner and select Show All Devices to list all detected disks and volumes.
  • Choose the target disk or volume at the left sidebar and then click First Aid.
  • Click Run on the popup window that asks if you'd like to run First Aid.
  • Wait until the First Aid finishes running.

Run First Aid check your drive

If Disk Utility reports that the operation is successful or has been repaired, you're done. Check if you can access that disk or, your Mac goes normal.

How to run First Aid from Mac Recovery Mode?

Usually, if you have problems with the startup disk (Macintosh HD volume), like Mac won't boot, you have to run First Aid in macOS Recovery mode.

The tutorial to run Disk Utility First Aid from Mac Recovery Mode:

boot into macOS Recovery mode

  • Select Disk Utility from the macOS Utilities window and click Continue.

Open Disk Utility macOS Recovery mode

  • Click View and choose Show All Devices.
  • Select the Mac hard drive or startup volume at the left sidebar.
  • Click First Aid on the top menu of the Disk Utility.
  • Click Run on the popup to confirm running First Aid > Continue.

When the First Aid process is complete, it will give a hint. Then, you can click Done to close First Aid.

Click Done when First Aid process is complete

Disk Utility First Aid failed to repair the disk, what to do?

If Disk Utility First Aid failed to repair the detected errors or its process has failed, it shows that macOS can't repair the disk. Therefore, you can fix the disk under Mac Single User Mode or you can expand "Show Details" and see the detailed error code and message as below:

1. Object map is invalid.

2. Fsroot tree is invalid.

3. APFS metadata tree is invalid.

4. File system check exit code is 8.

First Aid failed to repair the disk

In such as situation, firstly, you'd better back up your data as much as possible. Here we offer several solutions for you to have a try to back up the data:

1. Back up the data with macOS built-in Time Machine. This way is only suitable for a bootable Mac computer backup.

2. Recover data with iBoysoft Data Recovery for Mac. If your Mac cannot turn on, you have to recover data from an unbootable Mac with the aid of professional third-party software.

Recover data

How to recover data from Mac that won't turn on?

This post offers 5 ways to recover data from the unbootable Mac. And the best way is running iBoysoft Data Recovery for Mac in Recovery mode. Read more >>

After backing up the data, you can reformat this drive with Disk Utility to make the drive working again, or if it is the Macintosh HD, reinstall Mac OS on it to enable your Mac to start up again.


1. Can I stop First Aid on Mac?

Yes, but it's not suggested. Force Quit First Aid may lead to disk corruption or data loss. If you insist on doing so, you can press these keys together: Option + Command + Esc (Escape) to force quit Disk Utility First Aid.

Or you can select Force Quit from the Apple drop-down menu and select the Disk Utility to force quit First Aid.

2. How long does disk utility first aid take?

Usually, running First Aid will require no more than five minutes. If there are no errors found on the target disk or volume, less time will use. If First Aid has found any errors on the disk or volume, it will take extra time to repair the errors.

3. Does First Aid erase data?

No. Disk Utility First Aid only checks and repairs the errors related to a Mac disk's file system format and directory structure. It cannot erase data on the drive.

However, if you force quit First Aid when it is running, data loss may happen. And if your drive is corrupted heavily, First Aid cannot repair it. At this time, you also can't access data on the drive.