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

Sheryl Brown says:

March 7, 2016 at 3:38 am

I must Thank You for resolving mu issues. I am running OS X Yosemite 10.10.5

Reply
Tanya says:

February 4, 2016 at 3:50 am

What is a USN boot drive? I’m not a technology person? Can it be any usb?

Reply
1. Vishal says:
  
  February 5, 2016 at 10:32 am
  
  Hi Tanya,
  
  Hopefully you are trying to refer USB boot drive. You must be aware of USB which stands for Universal Serial Bus and it is used to support data transfer between two devices. With Boot Drive we mean that Operating system of a computer is burned (written) to a USB drive which makes it bootable. Using this bootable USB device we can boot (or start) a computer and perform data recovery or other tasks. Hope this helps.
  
  Reply
Iggy says:

December 2, 2015 at 3:16 am

I have an EXFAT partition on my 1TB usb hard drive however Stellar Partition Manager isn’t resizing it. Why so?

Reply
1. Vishal says:
  
  December 2, 2015 at 5:44 am
  
  Hello Iggy,
  
  Thanks for writing to us.
  
  Stellar Partition Manager doesn’t resize EXFAT partitions. You can create, delete, format and rename EXFAT drives however the software does supports resizing of HFS, FAT and NTFS formatted hard disk drives.
  
  Hope this information helps.
  Regards.
  
  Reply
Sam says:

November 19, 2015 at 7:14 am

Hi Vishal,

To resize my Mac startup disk, I am searching for the Stellar Partition Manager Registration key but unable to find any suitable download source. Please tell me how I can get the Registration key of Stellar Partition Manager Software?

Reply
1. Vishal says:
  
  November 20, 2015 at 4:39 am
  
  Hi Sam,
  
  To enjoy full features of the Stellar Partition Manager software you need to register the product by purchasing it from the website. I am sharing the buy now link of Stellar Partition Manager so that you can resize your Mac ASAP. Click to visit Stellar Partition Manager key registration page
  
  Reply
Owen says:

August 12, 2015 at 9:06 am

I was installing windows 7 on my Mac through boot camp when Disk Utility showed me a pop-up which says “Unrecognized file system”. This is 100gb of drive space I am talking off. Would your software resolve this issue?

Reply
1. Vishal says:
  
  August 13, 2015 at 3:51 am
  
  Hi Owen,
  
  Yes Stellar Partition Manager V3.0 will address your issue. Firstly you need to create a boot media using Stellar Partition Manager software. With the help of bootable media you need to boot into Mac and resize Macintosh HDD so that it claims that unrecognized spaces. To create bootable media and accomplish the task you need to register the software through Stellar Partition Manager Buy Now Page.
  
  Let me know if you have any further issues.
  
  Reply
Jacob says:

May 26, 2015 at 5:13 am

Suggest me some free data recovery apps. I have stupidity emptied my Trash.

Reply
1. Vishal says:
  
  May 28, 2015 at 3:11 am
  
  We recommend you try recovering your deleted files with a professional software and not with any free recovery apps. Free recovery apps aren’t reliable and won’t give you the desired recovery results. Through register software, you can run multiple recover modes such as Deleted File recovery, Formatted Drive recovery, Raw Recovery etc. You can organize filters to the software so that it recovers only specific files. Stellar Mac data recovery is free-to-preview software that allows preview of deleted, formatted and lost files in demo version. Once you are satisfied with the recovery performance of the software, you can purchase the software through its buy page. It is advisable to immediately scan your HDD with Stellar Mac data recovery software and avoid overwriting any new files to the drive.
  
  Reply
Timothy says:

May 21, 2015 at 10:28 am

My external hard drive formatted with Mac OS Extended Journaled stopped working yesterday. I ran Disk utility repair disk but it gave me back this message ‘Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files’

I unsure of my disk right now and need some solution asap.

Regards
Timothy

Reply
1. Vishal says:
  
  May 21, 2015 at 10:39 am
  
  Hey Timothy,
  
  Thanks for writing to us. Seems your hard drive is corrupt and beyond the repair of Disk Utility. You might erase this disk but this will lead to loss of data and erase process may end up unexpectedly. I advise you download & install Stellar Volume Repair tool and rebuild the drive corrupt directory structure. You can read the following blog post on HFS drive corruption from here
  
  Hope this helps. Please let me know if this resolves your issue.
  
  Regards
  Vishal
  
  Reply
Eugene says:

May 19, 2015 at 8:09 am

Why the software is not showing my Boot Camp partition? I am running iMac 2011 OS X 10.9.

Reply
1. Vishal says:
  
  May 19, 2015 at 8:13 am
  
  @Eugene. As of now, Stellar Partition Manager doesn’t resize or partition Boot Camp. Soon, the next version will be doing all partitioning tasks on boot camp.
  
  [Update: June 2015: Stellar Partition Manager supports BootCamp partition]
  
  Reply
Joel says:

May 18, 2015 at 3:13 am

My Mac is single drive partitioned but I created another partition named “Mac HD2” to download Yosemite on it. After the download & installation of Yosemite I wanted to remove Macintosh HD partition but keep music and video files and transfer them to Mac HD2. I want my Mac to be single partitioned again. How do I do this without loosing or messing up my Mac. I also have 1TB Seagate external hard drive. Please let me know how should I proceed.

Reply
1. Vishal says:
  
  May 18, 2015 at 3:23 am
  
  Hi Joel,
  
  I am going to help you resolve your issue. But first, please take backup of your important files to the external hard disk drive. I would also advise you to install Stellar Partition Manager on your Yosemite. When you start the software select your Apple drive. You will need to create a bootable DVD. Follow the steps mentioned in above reply (to Mabaker) in order to create boot dvd. When you Mac boots with the DVD, you can select your Macintosh HD and press :DELETE: icon from the software menu. The vacant space will then be reoccupied with your Mac HD 2. Now with the help of the Mouse pointer, drag the sidebar to resize your Mac HD 2 partition. You can resize the partition to take all the available free spaces on the Mac hard disk drive. Now click on the :PLAY: button to apply your changes. Once done, you Mac will start with Yosemite and your disk drive now becomes singe partitioned.
  
  Reply
Mabaker says:

May 13, 2015 at 5:32 am

My Disk Utility is unable to resize Macintosh HD. It is failing every time. How can I make this resizing possible? My Specs are MacBook Pro 2012 4GB 1TB.

Reply
1. Vishal says:
  
  May 13, 2015 at 6:00 am
  
  To resize the Mac startup disk, you need to create bootable DVD. Here is how you should proceed
  
  1) Download Stellar Partition Manager. It will ask you to create image of Macintosh HD. Click OK to proceed.
  2) The Image file created by the software needs t be burn on DVD. Use Disk Utility<<Burn to burn the image to a DVD.
  3) Restart Mac OS X and press OPTION key before Apple Logo appears. This will bring in the drive menu.
  4) Select the newly created boot DVD from this option. Now You Mac will Boot from the DVD.
  5) Stellar Partition Manager is mounted on the DVD. You can resize the Macintosh HD as required. Save the changes and restart Mac OS X.
  
  Software download link goes here
  
  Your Macintosh HD drive is now resized. Hope this helps.
  
  Reply