Mac Data Recovery

[Fixed] “Couldn’t Unmount Disk” Error on Mac

Written By Ruslana Lishchuk
Approved By Rohit Arora
Updated on 6 Jun, 2024
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Summary: Getting a message “couldn’t unmount disk” means that you won’t be able to erase, partition, reformat or do any other actions with the drive. This significantly limits your abilities, so we will describe the best ways to fix that error message in this article.

Almost any manipulation with a disk has a risk of data loss, so we recommend having reliable data recovery software at hand. With Stellar Data Recovery Professional for Mac, you can restore specific files or whole volumes of lost data with a few simple clicks.

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Why is Mac Giving You the “Couldn’t Unmount Disk” Error

Can’t unmount disk on Mac usually happens when you try to do some manipulations with the external or internal drive. The system won’t allow you to do anything if some other application or process uses the drive. You are also unable to partition, reformat or erase the disk you are currently booted from. Trying to perform any drive modifications would fail to give you the “couldn’t unmount disk” error message.

Before Fixing the “Couldn’t Unmount Disk” Error

We all know that it is recommended to do regular Mac backups. This becomes especially important whenever you try to fix any disk-related problems, including when you can’t unmount the disk on Mac. Make sure to use Time Machine or other third-party services to backup your Mac and protect your files. Use Stellar Data Recovery Professional for Mac if you encounter any kind of data loss and are in need of a quick and easy data recovery solution.

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

There are several different ways to fix the “couldn’t unmount disk” error message on Mac. This includes using Stellar Partition Manager software, Disk Utility, or Terminal. For your convenience, we have structured instructions into step-by-step guides that are easy to follow.

A. Fixing with Stellar Partition Manager Software

Stellar Partition Manager is an alternative to Disk Utility that allows performing various types of disk manipulations: create, hide, delete, resize and mount a volume. Use Stellar Partition Manager when macOS can not format, erase and repair the Mac hard drive or a volume due to the “couldn’t unmount disk” error. Formatting the hard drive or partition scheme will recreate a new HFS file structure on the hard drive, which will be free from cryptic errors. You can also use this software to create a bootable DMG and load the system from it instead of the external drive.

To format the drive with Stellar Partition Manager:

Install and run the software from the Applications folder.
Choose the hard drive on the left.
Click on Format on the top toolbar.
Wait until the process is ready in the Task to-do list on the right.
Choose the task and click on Start.
Wait until the formatting process is done.

B. Using macOS Utilities

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.

The instructions to boot into the Recovery Mode are different for Intel-based and Apple silicon Mac models, but they are the same on any OS, so you can follow these instructions even if you are using the newest macOS Monterey.

To open macOS Utilities on Apple Silicon:

Shut down your Mac.
Press and hold the Power button.
Release the button once you see ‘loading startup options’ on the screen.
Click on Options and Continue.
Type in username and password.

To open macOS Utilities on Intel Mac:

Shut down your Mac.
Wait for a few seconds.
Power your Mac while holding Command + R on the keyboard.
Release the buttons once you see the Apple logo.

Once you follow these instructions, you will see the macOS Utilities window. From there you can open Disk Utility which allows you to unmount the drive and perform various types of other disk-related actions.

C. Unmount a Disk Using Terminal

If previous steps didn’t work, you can use Terminal to fix “can’t unmount disk” on Mac. Open Terminal from the Recovery Mode if you need to unmount the drive you are currently booted from. You can use it from the Normal Mode if you want to unmount any external drive.

To unmount a disk in Terminal:

Open Terminal in Applications > Utilities or choose Terminal from Utilities in Recovery Mode.
Type diskutil list in the Terminal window.
Press Return to see the list of connected disks.
Note or copy the name of the disk you want to unmount. The identifier example: ‘disk0s1’.
In Terminal type sudo diskutil unmountDisk /dev/disks1 (make sure to change ‘disks1’ with the name of the drive).
Press Return and enter the admin password.

Terminal > sudo diskutil unmountDisk /dev/disks1

FAQ

How Do I Force Unmount Macintosh HD?

The system can’t unmount the disk on Mac that you are currently booted from. To force unmount Macintosh HD you need to start from an external drive, bootable USB, or Recovery Mode. After that, you can use Disk Utility or Terminal to unmount the internal drive.

What is the Mount on Mac Disk Utility?

Mounting the disk means making its content available for macOS to read and write. Usually, the mounting process happens by the system automatically, but you can also manually mount and unmount a drive in Dist Utility.

How Do You Unmount a Disk on a Mac the Right Way?

Open Disk Utility, choose the needed drive, and click on Unmount to unmount a disk. To eject any external drive, you can use Finder. Choose the drive on the left of the Finder window and then right-click and choose Eject. You can also unmount an external drive by dragging the icon into Trash.

How Do I Fix an External Disk that Won’t Unmount?

Usually, you will see “can’t unmount disk” on Mac when some application or process is using the drive you are trying to unmount. Use Force Eject to fix an external disk that won’t unmount. Another option is to find the application using the disk and quit it. After that, you can try to unmount the drive once again. This way is safer, as using Force Eject may damage the drive or data on it.

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About The Author

Ruslana Lishchuk

Ruslana is a tech content writer whose true passion is finding out about everything Mac-related. She specializes in creating macOS guides and tips & tricks. In her spare time, you’ll find her doing yoga or discovering local coffee shops in search of the best filter coffee.

80 comments

Santiago Romero says:

January 9, 2017 at 5:10 am

Hi Vishal,

I messed up my hard drive by erasing it with terminal while trying to format after it showed me Couldn’t Unmount Disk Error. The hard drive had some important data which I formatted accidentally. Do you have free mac data recovery software for OS X El Capitan?

Reply
1. Vishal says:
  
  January 9, 2017 at 9:04 am
  
  Hi Santiago,
  
  Here is the free Mac data recovery registration page.
  Good Luck.
  
  Thanks,
  
  Reply
Vishal says:

November 11, 2016 at 9:42 am

If you are unable to boot your system from the other disk, please go through the below solution:

1. First, Download the OS X firmware from the official App Store
2. Now, take an HDD and format it to OS X extended journal
3. Create a GUID table partition
4. Then, further install the OS X on it
5. Now, press the opt n reboot your system
6. Now select the external HD recovery mode
7. Finally, you will be able to format your Mac Hd in disk utility

I hope the solution will be helpful for you.

Reply
Audrey Hain says:

November 10, 2016 at 10:12 am

Hi, I am a MacBook Pro user, and I am unable to boot my Mac system from other disk. Please give me some suitable solution so that I can further use my MacBook Pro.
Thanks in advance.

Reply
Johnathan Melton says:

November 5, 2016 at 10:04 pm

Ok trying to wipe the mac pro completely but I can’t cause I can’t unmounted a partition drive so I tried a bunch of terminal ways to unmounted but keep getting a at least one volume could not be unmiunted

Reply
1. Vishal says:
  
  November 7, 2016 at 2:37 am
  
  Hi Johnathan,
  
  Do you have the backup of your Mac? If yes, then go to OS X utilities and format the entire hard disk drive. Disk Utility gives you options to secure delete the partitions and hard drives.
  
  Thanks.
  
  Reply
Sherri says:

October 18, 2016 at 8:00 pm

Hi, I cant seem to use my 1 TB hard drive on my macbook air (it has an NTFS system) and disk utility says erase process has failed. Press done to continue

Reply
1. Vishal says:
  
  October 19, 2016 at 2:24 am
  
  Hi Sherri,
  
  Mac can’t write to NTFS formatted hard drive but Stellar Partition Manager can help you format, resize, create, delete or hide NTFS partitions. Please download the demo version for a free evaluation.
  
  Thanks.
  
  Reply
Milton L. Scales says:

July 15, 2016 at 3:26 am

Couldn’t get around this problem until I found the solution mentioned by you. Used diskmaker x to make an el capital boot disk then followed your steps and it worked on my 2013 MacBook Pro with Yosemite version. Many-2 thanks for such a valuable blog post.

Reply
Dina B. King says:

May 23, 2016 at 3:31 am

I am trying to restore my Mac OS X El Capitan from an external drive to my Mac HD. But, whenever I try to repair my hard drive, it gives me an error message, “Couldn’t unmount disk”. Same goes when I try to erase the disk. Please tell me what should I do now?

Reply
1. vishal says:
  
  May 25, 2016 at 3:25 am
  
  Hi Dina,
  You can use Stellar Partition Manager Software to format the hard-drive of your Mac OS X extended Journaled file system. Formatting the HD will have recreated the new file structure on your hard drive and ‘Couldn’t unmounts disk’ will also resolve.
  
  Reply
John says:

April 7, 2016 at 8:50 pm

MacBook Pro 2011
2.2 GHz Intel Core i7
8GB 1600 MHz DDR3
OSX 10.9.5

I replaced my optical drive with an HDD Caddy and installed a 1 TB 2nd internal HD to save files on. Operating system is on the a seperate SSD internal drive in the standard drive bay. I tried formatting/erasing the 2nd HD numerous times with Disk Utility and it would continue adding time to the process up to 22+ hours. After changing the security options and trying to format, it finally said there were errors on the disk. Purchased new HD and it initially recognized disk when formatting. Error came up, can’t unmount disk. I tried booting up off an external osx drive, and now it won’t even recognize the disk. Tried again with internal osx drive and still won’t recognized 2nd drive. Any ideas? Thanks

Reply
1. Vishal says:
  
  April 8, 2016 at 3:10 am
  
  If Disk Utility is failing again & again to format the hard drive then you can try formatting with Stellar Partition Manager utility. Hope this helps.
  
  Reply
Alysia says:

March 15, 2016 at 3:35 am

I’m trying to format a new external hard drive and it is not working. It is a Seagate 1TB drive. When I go into Disk Utilities > Erase tab > change Volume Format to Mac OSX Extended > click erase, it keeps saying disk “Erase failed with the error: File system formatter failed.”

Reply
1. Vishal says:
  
  March 15, 2016 at 10:01 am
  
  Hi Alysia,
  
  What version of OS X you running? Could you also let me know the file format to which your external drive was formatted before this error?
  
  Thanks
  
  Reply
Miguel Starkey says:

March 7, 2016 at 3:40 am

How should I access my external hard drive partition which is unmountd on OS X El Capitan 10.11.2

Reply
1. Vishal says:
  
  March 8, 2016 at 2:54 am
  
  Hi Miguel, you have to run Stellar Mac data recovery software to recoup files from the unmounted hard drive. Here you can check out the KB article for the same.
  
  Reply