First Aid in Disk Utility Failed with an Error: Solutions for macOS

Why First Aid Might Fail?

First Aid in Disk Utility is a powerful tool for checking and fixing file system errors on macOS disks (APFS, HFS+). However, it doesn't always resolve the issue. Common causes of failure include:

• Physical disk damage (bad sectors, SSD wear).
• Critical file system errors that First Aid cannot automatically repair.
• Disk in use by system processes or applications (e.g., Time Machine, Spotlight indexing).
• Disk structure corruption (e.g., GPT partition damage).
• Insufficient space for temporary recovery files.

If First Aid reports that it cannot complete the check or repair, don't panic. There are several sequential ways to solve the problem, starting with simple steps and moving to more complex ones.

Solution 1: Check Disk Usage and Try Again

Before taking deeper action, ensure the disk is not in use. First Aid requires exclusive access.

1. Close all applications that might be accessing the disk:
   • Finder (if the disk appears on the desktop or in the sidebar).
   • Time Machine (if a backup is in progress).
   • Sync applications (Dropbox, Google Drive).
   • Terminal or other utilities that have the disk open.
2. Stop Spotlight processes (indexing can lock the disk):

   sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
   

   
   After running First Aid, remember to restore the index:

   sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
   

3. Restart your Mac and immediately launch Disk Utility (don't open other programs). Select the disk in the left panel and click First Aid → Run.

⚠️ Important: If Disk Utility reports that the disk "cannot be unlocked" or "is in use," proceed to the next solution.

Solution 2: Run First Aid in Recovery Mode

macOS Recovery Mode loads a minimal system, allowing you to check disks without conflicts from system files.

1. Restart your Mac and immediately hold Command (⌘) + R until the Apple logo appears.
2. From the Utilities menu, select Disk Utility.
3. In the left panel, select the primary physical disk (not the volume), then click First Aid.
4. If First Aid runs and completes successfully, restart your Mac in normal mode.

💡 Tip: Recovery Mode also provides access to Terminal (from the Utilities menu), allowing you to manually run fsck commands (see Solution 3).

Solution 3: Use Terminal to Manually Run fsck

If the graphical First Aid doesn't help, try the fsck (file system check) utility in Terminal. Be careful: selecting the wrong disk can lead to data loss.

1. Identify the disk identifier:

   diskutil list
   

   
   You'll see a list of disks. Example output:

   /dev/disk0 (internal, physical):
      #:                       TYPE NAME                    SIZE       IDENTIFIER
      0:      GUID_partition_scheme                        *1.0 TB     disk0
      1:                        EFEF 512 B                   disk0s1
      2:                 Apple_APFS Container disk1         1.0 TB     disk0s2
   
   /dev/disk1 (synthesized):
      #:                       TYPE NAME                    SIZE       IDENTIFIER
      0:      APFS Container Scheme -                      +1.0 TB     disk1
                                    Physical Store disk0s2
      1:                APFS Volume Macintosh HD            900.0 GB   disk1s1
   

   
   We're interested in the physical disk (e.g., disk0), not the volume (disk1s1).
2. Unmount the disk (do not physically disconnect it):

   diskutil unmountDisk /dev/disk0
   

   
   If the disk is the system disk, you won't be able to unmount it in normal mode. In that case, restart in Recovery Mode and run the command there.
3. Run the check depending on the file system:
   • For APFS (modern Macs):

     fsck_apfs -n /dev/disk0
     

     The -n flag means check-only (no repair). To repair, replace with -y, but only after backing up your data.
   • For HFS+ (older disks):

     fsck_hfs -fy /dev/disk0
     

     Flags: -f (force check) and -y (automatic repair).
4. Analyze the output. If fsck finds and fixes errors, repeat the check until you see the message ** The volume appears to be OK.
5. Remount the disk:

   diskutil mountDisk /dev/disk0
   

⚠️ Important: If fsck reports unrecoverable errors or physical damage (e.g., I/O error), the disk likely needs replacement. Back up your data immediately.

Solution 4: Create a Bootable External Drive and Check the Disk

If the issue is with the system disk (Macintosh HD) and you cannot unmount it in normal mode, create a bootable USB drive.

1. Prepare an external drive (USB flash drive or external SSD) with at least 16 GB of space, formatted as APFS.
2. Download macOS from the App Store (e.g., Ventura or Sonoma) on another working Mac, or use an already downloaded installer image.
3. Create the bootable drive via Terminal:

   sudo /Applications/Install\ macOS\ [Version].app/Contents/Resources/createinstallmedia --volume /Volumes/[Drive_Name]
   

   Replace [Version] with the macOS version (e.g., Ventura) and [Drive_Name] with your volume's name.
4. Boot from this drive:
   • Insert the drive into the problematic Mac.
   • Restart and hold Option (⌥) to choose the boot disk.
   • Select the installer drive.
5. From the Utilities menu, launch Disk Utility and run First Aid on the system disk.

Solution 5: Back Up and Reinstall macOS

If all previous steps fail, system files or disk structures may be corrupted. In this case:

1. Back up accessible data:
   • Use Time Machine (if configured) in Recovery Mode.
   • Manually copy files to an external drive via Finder (Finder is also available in Recovery Mode).
   • For complex cases, use data recovery utilities (e.g., Disk Drill, Data Rescue).
2. Reinstall macOS:
   • In Recovery Mode, select Reinstall macOS.
   • This overwrites system files but may preserve user data (if the disk isn't severely damaged).
   • If reinstallation fails, you may need to fully format the disk (in Disk Utility → Erase) and then install macOS. This will erase all data on the disk!

How to Prevent First Aid Errors in the Future?

• Regularly back up data using Time Machine.
• Avoid force-shutting down your Mac (use the Apple menu → Shut Down).
• Don't fill your disk completely — leave at least 10–15% free space.
• Avoid using uncertified cables and adapters for external disks.
• Check the disk monthly with First Aid, especially before important operations.

What If the Error Persists After All Steps?

If First Aid continues to fail even after reinstalling macOS, this may indicate physical disk damage (especially for HDDs) or SSD cell wear. In this case:

1. Check the disk's S.M.A.R.T. status via the System Information utility (Apple menu → About This Mac → System Report → SATA/SATA Express or NVMExpress).
2. Contact Apple Support or an authorized service provider for diagnostics.
3. Replace the disk (for MacBook/iMac this can be challenging but possible) and restore data from your backup.

Summary: A First Aid error is a serious signal about disk health. Act sequentially: from simple (closing apps) to complex (Recovery Mode, Terminal, reinstall). Always maintain an up-to-date backup.