Mac Data Recovery

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

Written By Ruslana Lishchuk
Approved By Rohit Arora
Updated on 6 Jun, 2024
Min Reading 3 Min
Share

Table of Content

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.

Free Download100% secure

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.

Was this article helpful?

YES0

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

Lou Frasier says:

December 22, 2017 at 10:32 am

After update my Mac OS, I couldn’t get previous screen. I tried to check everything in disk utility. This Information really helped me! The first solution work perfectly. Thanks for given me such a wonderful Information.

Reply
1. Shailendra Kumar says:
  
  December 29, 2017 at 3:21 am
  
  Hello Lou,
  Thanks for reading and using our software.
  
  Reply
Skuto9 says:

December 22, 2017 at 8:28 am

Hey. I am unable to delete/format main disk on mac book pro late 2009. (10.6.8)
When using disc utility the bars in erase section are not highlighted at all..(cant be chosen)
When using -sudo- in terminal with “diskutil” erase.. Also brings error -10000 could not unmount disk
Tnx in advance

Reply
1. Vishal says:
  
  January 3, 2018 at 3:56 am
  
  Hello Skuto9
  
  Kindly follow the below-mentioned steps to create a bootable DMG and to perform format/delete operation on the boot drive:
  
  1. Run Stellar Partition Manager after downloading it from here
  
  2. Select boot volume and click Create Bootable DMG.
  3. Click on Create Image button. Select the destination to save the disk image and click Choose to begin the image creation process.
  4. After the image is created, double-click on the created image to mount it.
  5. Attach external media to your computer and open Disk Utility from ‘/Applications/Utilities’.
  6. Format external media in ‘Mac OS Extended (journaled) with ‘GUID Partition Table’ Partition Map Scheme’.
  7. Select a mounted image from the left panel of Disk Utility and select Restore tab.
  8. Drag mounted an image to source and external media to destination and press Restore button.
  9. Use your external media to boot your computer after Restore is completed successfully.
  
  Note: Create Bootable DMG option is available for boot volume only. Do not stop the image creation process in the middle. It may corrupt your hard disk
  
  Reply
Teddy says:

October 23, 2017 at 5:17 pm

hi, my mac is actually shutting it self down after a silver bar appears on the screen and then it just shuts down without booting up. i tried with holding cmd,option,R to get into recovery mode. when i tried to reinstall the os it says that your drive is locked. is there any option that i unlock my drive or not ?
Secondly i also tried to erase the whole drive to reinstall osx but then it says Disk erase failed and it just didnt erased my hard. what is the way to solve this issue, If the data goesm i dont care but i need a fresh working OS to use.
HELP ME

Reply
1. Vishal says:
  
  October 24, 2017 at 4:34 am
  
  Hi Teddy,
  
  Did you encrypt your hard drive recently? In recovery mode, try selecting the disk at the hard drive level and then erase it. It seems there might be some issue with your hardware. Are you able to run Apple hardware test? You must backup your important data and try re-installing the macOS using a bootable USB. You can create one for macOS High Sierra.
  
  Reply
Erik says:

September 5, 2017 at 9:12 pm

Hey people,

I have a problem with the mac. I erased the disc and now when i turn it on it’s showing me a logo like ‘no folder’ … cmd+r is not working… what should I do?

Reply
1. Vishal says:
  
  September 6, 2017 at 6:06 am
  
  Hi Erik,
  
  It seems you have formatted the Mac startup disk and hence the Mac is unable to locate your OS. Did you try Recovery Mode by pressing Option before start-up? If you are able to go through Recovery Mode then restore Time Machine backup. Alternatively, try Internet Recovery to restore macOS. Erik, if after restoration you find that your data is lost or missing then you have to use a data recovery software. I recommend Stellar Mac Data Recovery for formatted hard drives. Do let know further.
  
  Reply
James says:

August 8, 2017 at 7:36 am

Helpful article Vishal, thank you. After 20 hours of trying I follow your instructions and it’s done within 15-20 minutes! External Bootable, additional Internal HDD and Internal SSD with High Sierra +APFS all now resized and reorganised.

Reply
Anjum says:

July 30, 2017 at 2:51 pm

Hi Vishal,

I have a late 2011 13.3″ MBP, running OS Sierra.
I was trying to do a clean OS restore, using the Recovery Mode.
So tried I booting the system using Command + R, and went to the disk utility screen. When I try erasing my Internal Disk, it does not go through, and it says unable to unmount disk. I tried the first Aid, and that worked fine.

Any help with this would be highly appreciated. Thank you!

Reply
1. Jyoti Prakash says:
  
  August 11, 2017 at 5:10 am
  
  Hi Anjum,
  
  Did you try erasing the drive at hard drive level or partition level?
  
  Best Regards
  Vishal
  
  Reply
Harvey Haynes says:

June 5, 2017 at 5:09 am

Hi Vishal,
is it possible to recover files from a hard drive that shows couldn’t get unmount disk error?

Reply
1. Vishal says:
  
  June 5, 2017 at 5:15 am
  
  Hi Harvey,
  
  Yes, you can recover your files with Stellar Mac Data Recovery software. I recommend you run the free trial of the application to preview all recoverable files.
  
  Reply
  1. Yankee says:
    
    June 21, 2017 at 3:31 pm
    
    Hello Vishal.
    
    I wanted to Encrypt My External Hard drive using Disk Utility, but i ended up erasing my whole files and document in my External hard drive through disk utility, please is there anyway i can recover files? because no files in my hard drive right now.
    
    Thanks
  2. Vishal says:
    
    June 22, 2017 at 2:33 am
    Hello Yankee,
    Please download Stellar Mac Data Recovery and run a free scan on your external hard drive to recover files formatted accidentally. Here are the steps to recover files using the software:
    
    Start New Scan
    
    Select external drive
    
    Run Advance Scan and start scan
    
    Preview files
    
    Register the software
    
    Recover (Save) your data
Ling Peng says:

April 2, 2017 at 5:10 pm

Hi there
It’s really interesting to ready your article. I have just recently upgraded to Sierra, but I fund that there are a few things not working.

the most important one is my Iphoto not working anymore. I understand that iphoto has been replace by photos, but as my Iphoto library is located at my external drive, therefore the photos did not convert my iphoto automatically. I have tried many ways to copy into photos, but didn’t work. it sounds like that the file has problems, which I can’t even copy it to any drive. help please! Ling

Reply
Chris says:

February 23, 2017 at 4:48 pm

Hello I’m new to Apple Imac and have a 2007 version Mac Desktop that was given to me and I by mistake reset the computer but I didn’t save I guess the drives or whatever it is that I needed and now it tells me temporarily unavailable and also it will not let me do the partition it says failed with error couldn’t unmount disk. Please help thanks

Reply
1. Vishal says:
  
  February 27, 2017 at 5:33 am
  
  Hi Chris,
  
  Don’t you have a Time Machine backup of your Mac system? Press Command + R before Mac startup to go into Mac OS X Utilities. From there, you can restore the OS X through Time Machine, Internet Recovery or by Reinstalling OS X.
  
  Thanks,
  
  Reply
Harry says:

January 30, 2017 at 3:50 pm

Hey,
I have a Mac 2012 lion. I am unable to boot it and thus tried using disk utility to reinstall os but
It’s says unable to unmount the disk.
Can u help me what exactly shd I do and how to boot the Mac using a external drive.

Reply
1. Vishal says:
  
  January 31, 2017 at 2:31 am
  
  Hi Harry,
  
  Can you create a USB bootable disk from another Mac system and then try to reinstall a fresh copy of OS X? You can create a macOS Sierra rescue disk also, however, a handy backup must be by your side.
  
  Thanks.
  
  Reply