Mac Getting the “Couldn’t Unmount Disk” Error and How to Fix It? (2022)

The Disk Utility on Mac is a very useful system tool for fixing specific disk problems. For example, you can run a disk check when your apps quit simultaneously, an external drive is not working properly, or your Mac won’t startup. Disk Utility will check the health of your hard drive and repair any disk errors if possible.

Disk Utility usually works smoothly, but there are times when frustrating errors occur and prevent the process from being completed. One of the common errors encountered when using Disk Utility is the “Couldn’t Unmount Disk” error. When this error pops up, any attempted task gets stopped right in its tracks.

What is the “Couldn’t Unmount Disk” Error on Mac?

The “Couldn’t Unmount Disk” error can happen during formatting, partitioning, disk verification and repair, or any task that the Disk Utility undertakes. What makes this error frustrating is that there is usually very little to no additional information provided by the error message, making it more challenging to resolve the problem, And based on the error message, it is even harder to determine what the problem is all about.

Here are some variations of the error message that Mac users encounter, depending on the process being executed when the error happened:

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  • Disk Erase failed.
    Disk Erase failed with the error:
    Couldn’t Unmount Disk.
  • Partition failed
    Partition failed with the error:
    Couldn’t Unmount Disk.
  • Disk Utility stopped verifying (letter of the hard disk)
    Couldn’t Unmount Disk.
  • Volume Erase failed
    Volume Erase failed with the error:
    “Couldn’t Unmount Disk”.

Once this pops up, the current process gets halted and could no longer proceed, affecting any troubleshooting process or disk repair you might be doing.

What Causes the “Couldn’t Unmount Disk” Error in Disk Utility for Mac?

When your Mac is getting the “Couldn’t Unmount Disk” error when using the Disk Utility, it is possible that the boot drive cannot be modified because it is being used by some process or an application. For example, a file from the disk you are trying to erase could be open, which means that you can’t proceed with the erasing unless all the files are closed.

Another possible reason is the presence of malware. When a malicious software is running in the background and wreaking havoc on your Mac, you might get the “Couldn’t Unmount Disk” error when you try to do something with your hard drive. This is because the malware might be making changes to your hard drive without you knowing it.

Other factors you should look into include corrupted system files, bad hard drive sectors, or insufficient permissions. Whatever the reason is, resolving this “Couldn’t Unmount Disk” error should be your priority because it might lead to further disk damage or other hard drive issues.

How to Fix the “Couldn’t Unmount Disk” Error on Mac

If your Mac is getting the “Couldn’t Unmount Disk” error, don’t worry because there are several ways to handle this problem. But before you do so, here are some of the basic troubleshooting you should take care of first:

(Video) Disk Erase failed with the error: Couldn’t unmount disk. macOs

  • Close all applications and files before attempting the repair.
  • Make sure you have enough permissions to read and write to the drive you want to modify.
  • Run a scan to check for the presence of malware. Delete any malicious software detected using your antivirus and delete all related files.
  • Disable your security software after running the scan because it might prevent the processes from pushing through.
  • Declutter your system by cleaning up your computer with a Mac cleaning tool. This should fix any errors related to corrupted junk files or cached data on your Mac.
  • Restart your computer.

Once you’ve completed the steps above, you can now proceed with the main solutions:

Solution #1: Use a USB Boot Drive to Repair the Hard Drive.

If “Couldn’t Unmount Disk” error occurs when you are trying to modify the boot drive, the easiest solution is to boot your Mac using another drive, and then run Disk Utility from that disk. You can use an installation drive or a recovery drive, as long as it is bootable and it is separate from the primary boot disk where your macOS is installed.

Here are the steps you need to follow to resolve this error using a USB boot drive:

  1. Connect the USB boot drive to your Mac, then reboot.
  2. While restarting, hold down the Option key button and choose the attached boot drive.
  3. In the boot menu, choose Disk Utility.
  4. Click First Aid at the top menu to verify the disk.
  5. Once your disk has been verified, you can then proceed with the task you were trying to perform when the error occurred.

Solution #2: Use the Recovery Partition.

If the “Couldn’t Unmount Disk” error message appears when doing First Aid on your disk or formatting a non-boot disk, the first solution will not work. If this is the case, you can try resolving the error using Recovery Partition.

Here’s how to do it:

  1. Reboot your Mac.
  2. While booting up, hold down the Option key to boot using the Recovery Partition.
  3. Next, click on Disk Utility from the boot menu.
  4. Click First Aid to verify the disk or select Erase to format the disk if needed.

Keep in mind that this method will only work if the disk that is throwing the error is not the same as the primary boot partition where the Recovery Partition is saved.

Solution #3: Use Command Prompt to Force Unmount the Disk.

If the above methods don’t work and your disk is pretty stubborn, you can attempt to fix this error by forcing to unmount the disk using commands.

To do this, follow the steps below:

(Video) Solution Disk Erase Failed with error Couldn't unmount disk mac

  1. Launch Terminal by navigating to Finder > Go > Applications > Utilities.
  2. In the Terminal window, type in the following command: diskutil list
  3. This will list down all the available disks on your Mac.
  4. Look for the disk that you want to force unmount and take note of the number of the drive.
  5. Type in this command next: sudo diskutil unmountDisk force /dev/diskx
  6. Replace /dev/diskx with the disk number of the drive you want to unmount (for example, dev/disk1).
  7. Wait for the process to be completed.

Solution #4: Use a Third-Party App.

If you don’t want to go through the trouble of booting using the USB boot drive or typing in commands in the Terminal, you can use a third-party tool instead. There are a lot of repair utilities to help you deal with this “Couldn’t Unmount Disk” error. These utilities can also be used to format, partition, erase, or modify your disk. Just make sure to choose a reliable app that can help you perform these tasks without any error.

Summary

The Disk Utility on macOS is a useful tool for fixing any disk-related issues or performing tasks that involve the hard drive. But this tool is not impregnable. Flaws, such as the “Couldn’t Unmount Disk” error, can happen from time to time. When this happens, simply follow the solutions listed above and you’ll be good to go.

Mac Getting the “Couldn’t Unmount Disk” Error and How to Fix It? (1)

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(Video) Couldn't Unmount Disk Error Mac

FAQs

How do I force my Mac to unmount a disk? ›

Unmount a disk member of a set
  1. In the Disk Utility app on your Mac, select the disk set that you want to unmount in the sidebar.
  2. Click the Unmount button in the toolbar or beside the disk set name.
  3. Disconnect the disk member that you want to unmount.

How do I fix my hard drive not mounted Mac? ›

External Hard Drive Is Not Mounting on a Mac: How to Fix
  1. Method 1: Change macOS Drive Display Settings.
  2. Method 2: Reconnect Your Drive.
  3. Method 3: Restart Your Mac.
  4. Method 4: Force Mount Your Drive With Disk Utility.
  5. Method 5: Use Disk Utility's First Aid Tool.
  6. Method 6: Reformat Your Drive.
Jun 23, 2022

What does unmount mean on Mac Disk Utility? ›

(1) To disconnect a disk drive or optical disc from a computer.

How do you remount a disk on a Mac? ›

If you eject a volume, you can use Disk Utility to mount the volume so that it's available in the Finder. In the Disk Utility app on your Mac, select the volume you want to mount. Click the Mount button .

Why can't I unmount my external hard drive Mac? ›

The system can?t unmount the disk you are currently booted from. So you need to start from a different volume to modify the internal drive. This can be achieved by booting your Mac from an external hard drive or macOS Recovery. After that, you can open Disk Utility from macOS Utilities to unmount the drive.

How do you unmount a hard drive? ›

If you're using Windows, right-click the drive in File Explorer and click "Eject" on the Manage tab. On a Mac, just select the drive in Finder and click the Eject button. To unmount in Linux, use "sudo umount" followed by the mount point.

How do you fix a hard drive that won't mount? ›

Troubleshooting external hard drives that will not mount
  1. Relaunch the Finder. ...
  2. Change the port. ...
  3. Plug in power adaptor (if available). ...
  4. Avoid daisy-chaining. ...
  5. Try a different connection type. ...
  6. Run general maintenance. ...
  7. Drive problems.
Apr 21, 2010

What does it mean when Macintosh HD is not mounted? ›

What does disk not mounted mean? If you are unable to view the Macintosh hard drive in disk utility, here the disk is not mounted. As the hard drive becomes inaccessible, except the erase button, all other operations become disabled or are greyed out. It is also possible that your Mac stops working.

How do I repair my Mac startup disk? ›

Repairing a disk
  1. Restart your Mac, and press Command + R, while it's restarting.
  2. Select Disk Utility from the macOS Utilities menu. Once Disk Utility has loaded, choose the disk you wish to repair - the default name for your system partition is generally "Macintosh HD", and choose 'Repair Disk'.

Is unmounting the same as ejecting? ›

"Unmount" will only unmount the partition,while "safely remove" will unmount all partitions, so the device can be removed without the danger of data loss or corruption. "eject" is like "safely remove", but will also eject the medium if that is possible, e.g. a CD or DVD. Has an ejection seat activated accidentally?

What does unmounting mean? ›

intransitive) to dismount. 2. ( transitive) to unfix from a backing or support; remove.

What happens if I unmount a drive? ›

What happens when a volume is unmounted? When a volume is unmounted, its drive letter is unassigned and may be used by another storage device. While unmounted, the volume's file system is inaccessible by regular reads and writes.

How do I reinstall Macintosh HD? ›

Restart your Mac. Choose Apple menu > Shut Down, press and hold the power button until “Loading startup options” appears, select Options, click Continue, then follow the onscreen instructions. In the Recovery app window, select Reinstall for your macOS release, click Continue, then follow the onscreen instructions.

Does mounting a disk erase data? ›

Mounting a drive does NOT alter the hard drive, although once a filesystem has been mounted it can be modified (unless it was mounted read-only) by typical filesystem operations like creating a directory/folder, creating files, modifying files, etc ....

What does mount and unmount mean on Mac? ›

Unmounting a disk is, not surprisingly, the opposite of mounting a disk. It takes a mounted disk and makes it inaccessible by the computer. External storage devices should typically be unmounted before being disconnected to avoid corrupting files.

How do I force eject my external hard drive? ›

How to safely eject an external USB hard drive on Windows
  1. Navigate to the bottom right corner of the bottom toolbar.
  2. If the USB icon is hidden, click the Up arrow.
  3. Locate the USB icon and find your external hard drive.
  4. Click Eject, and wait for a message stating it's safe to disconnect. A bell noise should also play.
Jul 8, 2022

Why can't I eject hard drive? ›

If you can't eject the external hard drive, you can reboot or turn off your computer, and this will close all programs and processes to make sure no programs are using the files on the external hard drive. After your computer restarts or turns off, you can try to eject the external hard drive.

Is it safe to force eject external hard drive Mac? ›

It is not at all safe to force eject external hard drives on your Mac. Why? That's because force ejection can open a box of many bad scenarios for your Mac, including hard drive data corruption. This happens because your machine uses something called a write cache while copying data from an external disk.

How do I unmount a partition? ›

Unmounting partitions
  1. Check the mounted partitions. Enter: ...
  2. Unmount the /mnt/old partition. Enter: ...
  3. Check for enabled swap partitions. Enter: ...
  4. Disable the /dev/sdb1 swap partition. Enter:
Sep 11, 2020

How do I unmount a USB drive? ›

Galaxy S22/S22+/Ultra: How to Unmount a USB Drive Before Ejecting

How do I use umount? ›

Examples
  1. To unmount all mounts from remote node Node A , enter: umount -n nodeA.
  2. To unmount files and directories of a specific type, enter: umount -t test. This unmounts all files or directories that have a stanza in the /etc/filesystems file that contains the type=test attribute.

How do I force eject my external hard drive? ›

How to safely eject an external USB hard drive on Windows
  1. Navigate to the bottom right corner of the bottom toolbar.
  2. If the USB icon is hidden, click the Up arrow.
  3. Locate the USB icon and find your external hard drive.
  4. Click Eject, and wait for a message stating it's safe to disconnect. A bell noise should also play.
Jul 8, 2022

Is it safe to force eject external hard drive Mac? ›

It is not at all safe to force eject external hard drives on your Mac. Why? That's because force ejection can open a box of many bad scenarios for your Mac, including hard drive data corruption. This happens because your machine uses something called a write cache while copying data from an external disk.

How do I force eject a USB? ›

Here is how you can use it to safely eject a USB drive:
  1. Launch File Explorer.
  2. Right-click This PC and select Manage.
  3. In the left pane, go to Storage > Disk Management.
  4. Right-click the external drive and select Eject.
Mar 30, 2022

Why can't I delete my Mac disk? ›

Fixes to solve the "Erase process has failed" error on Mac:
  • Reboot your Mac and run Disk Utility First Aid.
  • Erase the Volume.
  • Force unmount the drive with Terminal.
  • Force erase disk on Mac with Terminal.
  • Update the macOS.
  • Move down the Security level.
  • Delete partitions.
  • Format the drive in Safe Mode.

Why can't I safely remove my external hard drive? ›

Some users have reported that they are not able to safely eject their external hard drive like USBs etc. This issue is often caused by other processes that are using the contents of the drive or Windows USB drivers which prevent the removal of the external drive.

Why can't I safely remove my USB drive? ›

Why system can't eject USB disks? The most common reason behind this problem is that certain files in the USB drive may not be closed when you attempt to eject the external disk. Files stored on the USB mass storage device are used by other programs on computer, such as Microsoft Office.

Can't eject hard drive currently in use? ›

If the “This device is currently in use” error appears on your Windows 10 computer, try closing all files and programs on it. Then try to eject the removable device safely from the computer. Or you can refresh the desktop a few more times, and then try to eject the removable device.

Is it necessary to eject USB drive? ›

If you're using a PC that's running either an updated version of Windows 10 or any version of Windows 11 you can safely remove a USB flash drive from the machine at any time without ejecting it first. However, if you're using either a Linux PC or a Mac you still need to eject the drive before unplugging it.

How do I eject USB from Mac without icon? ›

How to Eject USB from Mac without Finder. If you've got a USB drive paired with your Mac, it shows up on your Desktop by default unless you've specifically tweaked it not to do this. To eject USBs with the right-click technique, just right-click on the device you want to detach and click on the “Eject Drive” button.

Is remove device the same as eject? ›

Eject removes the media from the device (e.g., ejects the CD tray) but doesn't remove the device itself.

How do I safely remove hardware and eject media? ›

  1. Click on the Windows icon and go to Settings > Personalization > Taskbar.
  2. Scroll down on the right pane of the window and click on "Select which icons appear on the taskbar"
  3. Toggle the switch for "Windows Explorer - Safely Remove Hardware and Eject Media" to Off.
Jun 30, 2020

Can I just unplug an external hard drive? ›

When you use external storage devices like USB flash drives, you should safely remove them before unplugging them. If you just unplug a device, you run the risk of unplugging while an application is still using it. This could result in some of your files being lost or damaged.

How do I reset my Mac startup disk? ›

Change your startup disk for every startup
  1. On your Mac, choose Apple menu > System Preferences, then click Startup Disk . Open Startup Disk preferences for me. If the lock at the bottom left is locked , click it to unlock the preference pane.
  2. Click the icon of the disk you want to use, then click Restart.

How do I reinstall OSX without recovery mode? ›

Install macOS from the bootable installer

Power down your Mac, and then restart it while holding the 'Option' key. The startup window should appear and display your USB drive with an accompanying “Install” tag. Select this drive, and then press the “Return” key on your keyboard.

What happens if I delete Macintosh HD data? ›

Also, because Macintosh HD contains macOS files, Mac users cannot erase, delete or edit Macintosh HD at will. If these files are modified or deleted, the Mac device will be damaged and will not turn on.

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