Check or repair your Mac's disk with Disk Utility First Aid

Why it happens

A sudden power cut, a forced shutdown or an external drive pulled out without ejecting can leave small errors in the way files are recorded on a disk. These can make files go missing, apps misbehave or a drive refuse to mount. First Aid checks that structure and repairs it, but it can't fix a disk that's physically failing.

How to fix it

1. Press Command-Space, type Disk Utility and press Return.

2. Choose View, then Show All Devices, so the sidebar lists each drive with its containers and volumes underneath.

   Disk Utility›View›Show All Devices

3. Select the volume you want to check. For the Mac's own disk that's usually Macintosh HD. Then click First Aid in the toolbar and click Run.

   Disk Utility›First Aid

4. When checking the startup disk, click Continue if asked. Your Mac may stop responding for a few minutes while it works, which is normal.

5. Read the result and click Done. To be thorough, run First Aid on each volume, then on its container, then on the disk at the top, in that order.

Still not fixed?

1. Back up straight away with Time Machine if First Aid found problems, even if it fixed them. Errors that come back can be an early sign of a failing drive.

   General›Time Machine

2. If First Aid says it can't repair the startup disk, run it from Recovery. On a Mac with Apple silicon, shut down, then press and hold the power button until you see the startup options, click Options and Continue. On an Intel Mac, hold Command-R as it starts. Choose Disk Utility and run First Aid again.

3. For an external drive, try a different cable and port, eject it properly before unplugging, and run First Aid again. If it still fails, copy off what you can and replace the drive.

4. If your Mac won't start at all, Recovery is also where you can reinstall macOS without erasing your files.

5. If First Aid keeps reporting errors it can't repair on the built-in disk, the drive may be failing. That's hardware: back up what you can and contact Apple Support or an Apple Authorized Service Provider.