# How to Use Disk Utility First Aid on Mac

> Run First Aid on volumes, containers and the disk in the right order, check the startup disk from Recovery, use diskutil verifyVolume, and read each result.

Published: 2026-10-13 | Updated: 2026-10-17

To run First Aid in Disk Utility, open **Disk Utility** from **Applications › Utilities**, choose **View › Show All Devices**, select the last volume under a disk, click **First Aid**, then click **Run**. Repeat for each volume above it, then the container, and finally the disk itself. For the startup disk, Apple recommends running the check from macOS Recovery. Back up first: [Apple's First Aid guide](https://support.apple.com/102611) says to make sure you have a current backup before you start, in case Disk Utility finds errors it cannot repair.

First Aid is a file system check, not a speed-up tool. It is worth running when apps quit unexpectedly, files are reported as damaged, an external disk will not mount or behaves oddly, or another tool tells you the disk has errors. Running it on a healthy disk once a week does nothing useful.

## What First Aid actually checks

Apple's [Disk Utility guide](https://support.apple.com/guide/disk-utility/repair-a-storage-device-dskutl1040/mac) says First Aid checks for and fixes errors related to the formatting and directory structure of a storage device. That is the file system's own bookkeeping: which blocks belong to which file, which folders contain which items, and how much space is free. When that bookkeeping is inconsistent, you see symptoms such as damaged files, wrong free-space numbers, or a disk that will not mount.

First Aid does not recover deleted files, does not remove malware, and, as Apple notes, does not detect or repair every disk problem. A disk can pass First Aid and still be failing physically.

## Containers, volumes and the order to check them

Modern Macs use APFS. With **Show All Devices** turned on, the Disk Utility sidebar shows three levels:

| Level | Example | What it is |
|---|---|---|
| Device | `APPLE SSD` or the name of an external drive | The physical disk |
| Container | `Container disk3` | An APFS container that shares space among its volumes |
| Volume | `Macintosh HD`, `Macintosh HD - Data` | What you see in Finder and use for files |

Apple's order is bottom up: on each device, start with the last volume, run First Aid, and keep moving up the list through the other volumes, then the container, then the device. On the startup disk, `Macintosh HD` is the system volume and `Macintosh HD - Data` holds your files and apps; Apple says to check the data volume as well when you check the startup volume.

## Back up before you repair

A repair changes the file system's structures. Most of the time that is what you want, but if the disk is already damaged, the files you care about should exist somewhere else first.

- If you use Time Machine, let a backup finish. Apple's [Time Machine guide](https://support.apple.com/104984) covers setup in **System Settings › General › Time Machine**.
- If a backup cannot complete because of disk errors, copy the files you cannot replace to another drive by hand, starting with the most important.
- Do not rely on a sync service as the only copy. A sync can copy a damaged file over the good one.

If the disk is an external drive that holds your only copy of something, copy that data off before running a repair.

## Run First Aid on an external disk or a data volume

1. Connect the disk and open **Disk Utility**.
2. Choose **View › Show All Devices**.
3. Select the last volume on that device in the sidebar.
4. Click **First Aid**, then **Run**, and follow the prompts. Disk Utility may need to unmount the volume to repair it, so close files that are open from it.
5. Click **Done** when it finishes. **Show Details** shows what it checked and repaired.
6. Move up the list: the remaining volumes, the container, then the device.

If the external disk does not appear in the sidebar at all, Apple suggests shutting down, unplugging nonessential devices, and checking the cable, connection and the drive's power before assuming the Mac or the drive needs service.

## Check the startup disk from macOS Recovery

Disk Utility can check the startup disk while macOS is running, but a repair usually needs the volume unmounted, and a startup disk cannot be unmounted while you are using it. Apple's guide says to restart in macOS Recovery to check your startup disk. [How to start up from macOS Recovery](https://support.apple.com/102518):

- **Apple silicon:** Shut down. Press and hold the power button until **Loading startup options** appears, click **Options**, then **Continue**.
- **Intel:** Turn on the Mac and immediately hold **Command-R** until an Apple logo or spinning globe appears.

In the Recovery utilities window, select **Disk Utility** and click **Continue**. Then run First Aid in the same bottom-up order: `Macintosh HD - Data`, `Macintosh HD`, the container, and the internal device.

Recovery is also the place to go when the Mac does not start fully, since Disk Utility runs from there without loading your normal startup software.

## The same checks in Terminal with diskutil

`diskutil` is the command-line side of Disk Utility. These commands only read:

```shell
diskutil list
diskutil apfs list
```

`diskutil list` shows every disk and volume with its identifier, such as `disk3s5` in the examples below (yours may differ). `diskutil apfs list` shows how APFS containers and volumes are grouped.

To verify a volume without repairing it:

```shell
diskutil verifyVolume /
diskutil verifyVolume disk3s5
```

The `diskutil` manual page (`man diskutil`) says `verifyVolume` checks the file system data structures of a volume, verifies any underlying storage system such as APFS first, and in certain cases can run live, including on the boot volume. `verifyDisk` checks a whole disk's partition map layout.

Repairs use `diskutil repairVolume` and `diskutil repairDisk`. The manual notes that a volume repair usually needs the target volume to be unmountable and the media to be writable, and that live repair of a mounted, writable volume is not supported. For the startup disk, that means running the repair from Recovery. Use the identifier from `diskutil list` and double-check it before running a repair; the commands act on whatever identifier you give them.

## What the results mean

| Result | What it means | What to do |
|---|---|---|
| The volume appears to be OK, or it was repaired | The file system structures are consistent now | Nothing more; click **Show Details** if you want to see what changed |
| Overlapped extent allocation errors | Two or more files occupy the same space on the disk, and at least one is likely damaged | Check each file Apple lists; most have aliases in a `DamagedFiles` folder at the top level of the disk. Replace or re-create what you can, and open and examine files with data you need |
| First Aid could not repair the disk, or the process failed | The damage is beyond what First Aid can fix | Try once more. If it still fails, back up as much data as you can, erase the disk, reinstall macOS if it is the startup disk, and restore your data |
| The disk is about to fail | The hardware itself is unreliable | Back up now and replace the disk. Apple says it cannot be repaired |
| The disk does not appear | Connection, power, or hardware problem | Check cables and power for external drives; otherwise the Mac or drive may need service |

All of these come from Apple's [Disk Utility guide](https://support.apple.com/guide/disk-utility/repair-a-storage-device-dskutl1040/mac). If problems continue after a successful repair, Apple notes that the disk may be physically damaged and need replacement.

Erasing is the step for a disk that First Aid cannot repair, not a substitute for a backup. An erase removes everything on the volume or disk you choose.

## What not to do

- Do not erase a disk to fix an error before copying the files you need off it.
- Do not keep running repairs on a disk that reports it is about to fail. Apple says that disk cannot be repaired; spend the time on a backup and a replacement.
- Do not run `fsck` by hand on a mounted volume. `diskutil` already runs the right checker and handles mounting for you.
- Do not treat First Aid as routine maintenance. A clean result on a working disk is the expected result, not a sign that something was fixed.

If the disk is fine but your Mac still freezes or restarts, the cause is elsewhere; [Mac frozen or keeps crashing](https://mole.fit/blog/mac-frozen-or-keeps-crashing) covers the other checks. For a full startup disk rather than a damaged one, see [Startup disk full on Mac](https://mole.fit/blog/mac-startup-disk-full).

## FAQ

### How do I run Disk Utility First Aid on a Mac?

Open **Disk Utility**, choose **View › Show All Devices**, select the last volume on the disk, click **First Aid**, then **Run**. Repeat for the other volumes, the container and the device. Check the startup disk from macOS Recovery.

### Can I run First Aid on my startup disk while using the Mac?

Disk Utility can check it, but a repair usually needs the volume unmounted. Restart in macOS Recovery, open Disk Utility there, and run First Aid on `Macintosh HD - Data`, `Macintosh HD`, the container and the device.

### What does "First Aid process has failed" mean?

First Aid found damage it could not fix. Run it once more; if it fails again, back up what you can, erase the disk, reinstall macOS if needed, and restore from the backup.

### Does Disk Utility First Aid delete files?

It is not meant to; it repairs the file system's structures. Files that were already damaged may be listed separately, for example in a `DamagedFiles` folder after overlapped extent errors. Back up before running it anyway.

### How often should I run First Aid on a Mac?

Only when there is a symptom: damaged files, a disk that will not mount, apps that crash while reading files, or an error from another tool. It is not a routine maintenance step.

---

Canonical HTML page: https://mole.fit/blog/how-to-use-disk-utility-first-aid-mac
Blog index for agents: https://mole.fit/blog/llms.txt
Site index for agents: https://mole.fit/llms.txt