“Couldn’t Unmount Disk” Mac Error | The Ultimate Fix

Errors and bugs can totally freak you out, you can get victimized by them knowingly or unknowingly. Also, Errors can not only affect your Mac but also they can make you consider the system is in real trouble.

Mind you, the majority of the errors and bugs are fixable. This time the error is related to the disk present in the Mac. Many users are encountering with disk error that accompanies a message as “Couldn’t Unmount Disk.

“couldn’t Unmount Disk” Mac Error | The Ultimate Fix

You can take this error as common, but many users don’t know how to fix it. Perhaps, some users attempt to make an incorrect move by considering the disk as corrupted and go for the new disk. Which is a complete miscalculating decision while the “Couldn’t unmount disk” error can get resolved.

Couldnt Unmount Disk Mac

Here’s everything you need to know about how to fix “Couldn’t Unmount Disk“. We will troubleshoot the disk in 3 ways to fix the error. Without wasting much of your time, let’s quickly begin.

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Why “Couldn’t Unmount Disk” Error Occurs on Mac?

“Couldn’t Unmount Disk” error mostly occurs when something goes wrong with the disk while making partitions on it. It could also happen due to modifications made on the disk.

When “Couldn’t Unmount Disk” Error Occurs on Mac?

Following are the reason’s when “Couldn’t Unmount Disk” errors occurs on Mac:

  1. When you try to modify the boot drive.
  2. The drive could be currently used by another application.
  3. When preferences have not given to a network drive or external drive if Mac’s internal drive is unable to work because OS X Recovery partition exists on physical drive.
  4. Incomplete formatting, or failed erased process of the disk.
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What is the Solution?

Good thing is that a valid solution is available that will help us to resolve the “Couldn’t Unmount Disk” Error on Mac.

Keeping the fact in mind that Disk Utility able to execute from the external drive, we can use it to boot Mac from another bootable drive.

Let there be any Mac OS X version as it doesn’t matter (assuming 10.7 to 10.14 and above), this error can be easily resolved only if Disk utility is present on the drive.

Anyways, let’s head towards the actual fixes.

Fix “Couldn’t Unmount Disk” Error with Recovery Partition

Mind you, this fix will not work if the error was caused by modifying the bootable disk while creating a partition or formating.

If that’s not the case, this fix is worth trying, here’s how to resolve the error with the recovery partition:

Step 1: Restart your Mac while pressing and holding the Option key, and then select to choose Recovery partition.

Step 2: A boot menu will appear, here, select to choose “Disk Utility”.

Step 3: Visit First Aid and try to repair the disk. Or go to Erase in order to format the disk.

Once the process is finished, check if the issue has resolved. If the issue is still there, then assume that the error is caused by modifying the bootable disk. Move on to the next fix.

Fix “Couldn’t Unmount Disk” Error with USB Boot Drive

This fix has worked for many users, so there are high chances that this will work for you as well. But before trying this method, make sure that the recovery drive is located in the drive (a separate copy of os installed on it).

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Step 1: Connect the USB boot drive to the Mac, and perform a system reboot, but don’t remove the USB drive.

Step 2: While your Mac is rebooting, press and hold the Option, and select the connected USB boot drive (indicated in orange color icon located at the boot menu).

Step 3: On the boot menu, select Disk Utility.

Step 4: Visit First Aid, verify the desk performs a disk repair (if necessary).

Step 5: Now do the process that has to remain incomplete due to the error.

Here, the USB bootable drive is referred to as a pen drive, or USB stick which should have Mac OS installed in it.

In case, if you’re using an installer disk instead of a USB bootable drive, then pull down the Utilities menu in order to access Disk Utility. (As mentioned in Step: 4)

Fix “Couldn’t Unmount Disk” Error using Command Line in Mac

To do so, users need to do the following:

Step 1: Go to Finder > Applications > Utilities, and open Terminal.

Step 2: Now, type the following command and press return:

diskutil unmountDisk force /Volumes/DRIVENAME

Here, just replace the DRIVE NAME with your drive’s name accordingly.
This command will force your drive to unmount. Now, check if the error has been resolved, if not then move on step 2.

Step 2: Now, type the following command, this will make you appear a list of the disk which are available on your Mac:

diskutil list

Now, you have to select a disk in order to do force unmount. For example, (/dev/disk1, /dev/disk2, /dev/disk3, etc). Make sure to remember the drive number.

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Step 3: Now, type the following command right before the drive:

sudo diskutil unmountDisk force /dev/disk2

Here, we have selected (/dev/disk2). In your case, it could be one of the rest of the disks.

Now, just press return to execute the command. Enter the administrator password if asked. This will easily force the drive to unmount.

Mind you, unmounting your drive forcefully will affect a drive like data loss. Do this if you are planning to format or erasing the disk

Fix “Couldn’t Unmount Disk” Error using Third-Party apps

If you don’t prefer to fix the issue using a USB boot drive or using the command line. You can go with third-party apps that are available to fix the “Couldn’t Unmount Disk” Error.

You can use Stellar Partition Manager Software. This will help you to resolve the issue.

How To Fix “couldn’t Unmount Disk” Error In Mac


All troubleshooting methods mentioned above are valid fixes. The easiest fix is a USB boot drive and using the command lines in Terminal.

Third-party apps might be helpful but we recommend you to go with a USB boot drive, and using the command line Terminal, as it is more reliable.

That’s it for now, hope this helps! We are glad to know your thoughts in the comment section below. Till then, stay tuned for more info.

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