How to fix "Couldn’t Unmount Disk" Error on Mac?

by Jake Doe - -


Issue: How to fix "Couldn’t Unmount Disk" Error on Mac?

I was trying to erase my drive on MacBook, but I received an error message saying “Disk Erase failed with the error: Couldn't unmount disk.” What does it mean? Is there something that I can do about it?

Solved Answer

“Couldn’t Unmount Disk” is the error that, in most cases, appear when users try to format internal disk by Disk Utility or repair it on the Mac device. Disk Utility is an important feature that helps to solve problems on the system. However, it can still fail to fix some of them or even deliver error messages like “Couldn’t Unmount Disk” error.

Due to the “Couldn’t Unmount Disk” error users might encounter these problems as well:

  • Inability to partition Mac HFS;
  • Inability to open particular files or programs;
  • Lost or corrupted data on the hard drive;
  • Sudden elimination of the running application.

"Couldn’t Unmount Disk” error fix 

“Couldn’t Unmount Disk” error is an error message that might pop up on your Mac’s screen when the device is not allowed to repair particular permissions or directories in Disk Utility,[1] for instance when trying to repair a hard drive. When a device cannot erase or partition the drive, users are delivered one of these error messages:

Disc erase failed couldn’t unmount disc.


Disk Erase failed with the error: Couldn’t unmount disk.

There are several reasons why users cannot complete the necessary tasks because of this error. Usually, the source of the error is a particular boot drive[2] which is modified or corrupted. The alert might also pop up when the driver is being used by other apps or processes. Sometimes, the issue is an internal drive.

However, the error might be triggered by malware as well. Nevertheless, Mac OS X is pretty resistant to various cyber threats;[3] security experts warn about an increase of Mac malware[4] that might sneak inside the device and might trigger various errors and problems.

How to deal with “Couldn’t Unmount Disk” error

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To repair damaged system, you have to purchase the licensed version of Intego Intego.

If you ever noticed other symptoms besides the error or the ones that resemble the virus attack, you should obtain a professional security software, such as Reimage, and scan the system with an updated tool.

If virus attack was not the problem, try the methods below that will help to fix “Couldn’t Unmount Disk” error. There are a few solutions for the issue, but users should try all of them of one of them doesn't work at first.

Check USB Boot Drive

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To repair damaged system, you have to purchase the licensed version of Intego Intego.
  1. Make sure that USB boot drive is attached to the device.
  2. Reboot the system. When rebooting hold the Option key. From the appeared menu select the attached boot drive.
  3. Access Disk Utility from the appeared Boot menu (however, if you use Installer disk, go to Utilities menu and click Disk Utility option).
  4. Go to First aid. Verify the disk and repair it if it’s necessary.

Once it’s done, try to complete the same task again. If the “Couldn’t Unmount Disk” error shows up again, try the second method.

Use Recovery Partition

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To repair damaged system, you have to purchase the licensed version of Intego Intego.

This method should help if the “Couldn’t Unmount Disk” error occurred when formatting a non-boot partition or caused by first aid. The Recovery partition is included in all new OS X versions. Therefore, follow these steps:

  1. Reboot Mac. When rebooting hold down the Option key.
  2. From the appeared menu choose Recovery partition option.
    MacOS reboot options
  3. In the appeared boot menu choose Disk Utility.
    – Go to First Aid if you want to verify and repair the disk.
    – Go to Erase if you want to format the disk.

Use the command line to fix “Couldn’t Unmount Disk” error

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To repair damaged system, you have to purchase the licensed version of Intego Intego.
  • Access Terminal application.
  • Input diskutil list line. 
    Terminal commands
  • When the list of all disks appears you need to found the disk that you want to force unmount.
  • Type sudo diskutil unmountDisk force /dev/diskx line.
  • Replace /dev/diskx with correct disk number.
  • Follow with steps further to forcibly unmount the disk from your Mac.

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Prevent websites, ISP, and other parties from tracking you

Private Internet Access is a VPN that can prevent your Internet Service Provider, the government, and third-parties from tracking your online and allow you to stay completely anonymous. The software provides dedicated servers for torrenting and streaming, ensuring optimal performance and not slowing you down. You can also bypass geo-restrictions and view such services as Netflix, BBC, Disney+, and other popular streaming services without limitations, regardless of where you are.

A VPN is also crucial when it comes to user privacy. Online trackers such as cookies can not only be used by social media platforms and other websites but also your Internet Service Provider and the government. Even if you apply the most secure settings via your web browser, you can still be tracked via apps that you are connected to the internet. Besides, privacy-focused browsers like Tor is are not an optimal choice due to diminished connection speed.

Therefore, to stay completely anonymous and prevent the ISP and the government from spying on you, you should employ Private Internet Access VPN. It will allow you to connect to the internet while being completely anonymous, prevent trackers, ads, as well as malicious content. Most importantly, you will prevent the illegal surveillance activities that NSA and other governmental institutions are performing behind your back.


Recover your lost files quickly

Unforeseen circumstances can happen at any time while using the computer: it can turn off due to a power cut, a Blue Screen of Death (BSoD) can occur, or random Windows updates can decide to reboot the machine when you went away for a few minutes. As a result, your schoolwork, important documents, and other data might be lost.

Additionally, you might also be attacked by malware that can corrupt your Windows or encrypt files with a robust encryption algorithm, and ask for a ransom in Bitcoin for the decryption tool. Cybercriminals might not deliver what they promised, however, so it is better to attempt alternative file recovery methods that could help you to retrieve at least some portion of the lost data.

Data recovery software is one of the options that could help you recover your files. Once you delete a file, it does not vanish into thin air – it remains on your system as long as no new data is written on top of it. Data Recovery Pro is recovery software that searchers for working copies of deleted files within your hard drive. By using the tool, you can prevent loss of valuable documents, school work, personal pictures, and other crucial files.

About the author

Jake Doe
Jake Doe - Computer technology geek

Jake Doe is a News Editor at Ugetfix. Since he met Ugnius Kiguolis in 2003, they both launched several projects that spread awareness about cybercrimes, malware, and other computer-related problems.

Contact Jake Doe
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