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

Denise Harman says:

December 1, 2020 at 12:46 am

I’ve attempted to install OS X on my MacBook Air. I get an error message stating no packages were eligible for install. I now can’t access my computer. It restarts over and over again. I don’t know what to do from here and need specific instructions so I don’t do more damage.

Reply
1. Vishal says:
  
  December 4, 2020 at 8:54 am
  
  Hi Denise,
  Your computer had been running with no battery, and therefore the hardware clock was reset to zero, and Mac OS X had a test against that condition. Here you can go to the terminal and change the operating system date. The date command can be used to change the time registered in the system clock. After that, you will be able to install OS X on your MacBook Air.
  
  Reply
Abhay says:

October 10, 2020 at 5:45 am

Hi Vishal,
Thanks for helping us in this forum. Since I have only 1 MAC system, with only 1 internal HDD which is unable to boot / unmount /erase, I can perform the Firstaid however it repairs but still can’t mount / erase the drive.Any help you can offer in this case?

Reply
1. Vishal says:
  
  October 12, 2020 at 4:01 am
  
  Hello Abhay,
  
  Please specify what task you exactly want to perform on your start-up disk? And, if your Mac isn’t booting then you can apply following tips:
  
  1) Create another bootable OS on an external drive and boot your Mac via it. Then try to mount your internal macOS disk.
  2) If you want to do data recovery then you can create a recovery drive via Stellar Data Recovery Professional for Mac.
  
  Please Read more about Mac hard drive recovery here.
  
  Please feel free to discuss further.
  
  Reply
Gilbert W Shepherd says:

July 19, 2019 at 9:53 pm

Hello,
My Macintosh HD is attacked by a virus or malware. I scan with antivirus software and deleted affected files. A large number of files are corrupted. Now my Mac does not mount the Macintosh HD, Please help me fix this problem!!

Reply
1. Vishal says:
  
  July 22, 2019 at 3:41 am
  
  Hi Gilbert,
  First, restart your mac Sometimes when you turn it back on, everything returns to normal.
  Secondly, Repair the unmounted Macintosh HD in recovery mode. The Macintosh HD is unable to be mounted in Disk Utility normally, you can try to fix it with Disk Utility’s First Aid in Recovery Mode.
  Third, fixed your Macintosh HD not mounted by the terminal.
  Fourth, run FSCK command in single-user mode.
  Last if have you lost your data so you can recover with the help of Stellar Data Recovery Professional for Mac. Thanks
  
  Reply
Kay Frazier says:

January 24, 2019 at 10:07 am

Hello Author,

Do Stellar Data Recovery also offer USB bootable drive along with the software?

Reply
1. Vishal says:
  
  January 25, 2019 at 4:52 am
  
  Hello Kay,
  
  Unfortunately, currently, we are not providing any bootable drive.
  
  Reply
Bradley Edward says:

November 22, 2018 at 9:56 am

I am running MacBook Pro 2016 with macOS Mojave 10.14. This Mac is unable to recognise external 128 GB SSD storage. Please help me recover as the SSD contains important projects and documents.

Reply
1. Vishal says:
  
  November 23, 2018 at 3:33 am
  
  Run First Aid on your SSD using Disk Utility. I suggest you to install Stellar Data Recovery Professional for Mac to recover your important documents and to avoid any data loss risk. The software scans your unrecognized SSD and list all the recoverable files. To save the files, you need to register the software.
  
  Reply
Phyllis Duckworth says:

July 11, 2018 at 6:09 am

How to recover data after disk2 doesn’t mount on my MacBook Pro?

Reply
1. Vishal says:
  
  July 11, 2018 at 8:36 am
  
  Leverage Stellar Mac Data Recovery and you can recover data from unmounted disk conviniently.
  
  Reply
Penney Wilson says:

June 3, 2018 at 2:36 am

Thanks for another informative blog. Where else could I get that kind of info written in such a perfect way? I’ve a project that I am just now working on, and I’ve been on the lookout for such information.

Reply
Sara says:

April 18, 2018 at 6:33 am

WD Passport (One TeraByte) not mounting on MACBOOK PRO. I can see it Applications > Disk Utility (greyed out) but not on Desktop. Ran First Aid from Disc Utility but it didn’t worked. Would you recommend some solution for data recovery?

Reply
1. Vishal says:
  
  April 18, 2018 at 6:41 am
  
  Hey Sara,
  
  Yes, we have solution for unmounted data recovery on MacOS. You can watch the tutorial video and then download Stellar Mac Data Recovery to recover your files.
  
  Regards
  Vishal
  
  Reply
SHAN says:

February 28, 2018 at 6:09 pm

I use MacBook Pro Mid 2012, 750GB HDD. Recently i bought it from my friend. It had OS X Mountain Lion installed. Then i upgraded it to Mac OS high sierra successfully. Then i made two partitions of my HDD and the process took me to install Mountain Lion again. I installed it and tried many times to upgrade to Mac OS high Sierra. But failed to installed. After 5 hours of download, the installation requires the system to restart but the restart is failed. I am very depressed and stuck with the mountain lion. i also tried to format the HDD with a single default partition “Macintosh HD’, but it says, partition error: couldn’t mount.

can anyone help me the way of installing Mac OS high sierra and of partitioning my HDD like it was before?

Reply
1. Vishal says:
  
  March 1, 2018 at 4:27 am
  
  Hello Shan,
  
  Thanks for contacting Stellar Data Recovery
  
  Did you try erasing the Apple hard drive via recovery mode? If not, then backup your Mac and boot into Recovery Mode by immediately pressing Command + R after restarting your Mac. Once in Recovery Mode, you can go to Disk Utility and erase the complete hard drive to a single partitioned drive. Here is a guide where you can install macOS High Sierra via Recovery Mode
  
  Reply
Clark Gable says:

February 22, 2018 at 10:14 am

Just the solution I was looking for ..This worked for me – easy and no separated USB drives required. Thanks!

Reply
1. Vishal says:
  
  February 23, 2018 at 4:42 am
  
  Hello Clark,
  
  Many Thanks for the feedback.
  
  Reply