There are some of motives why you may need to unmount a disk for your Mac. And you already know that earlier than you pull the plug, you must eject or unmount it. If you disconnect your USB stick or outside tough power with out first ejecting it, you’ll see an blunders message. 

Sometimes, while you attempt to do the proper component and eject it first, you’ll additionally see an blunders message, telling you it couldn’t be ejected.

However, even as ejecting does similar to unmounting, the mistake message that consists of the words ‘couldn’t unmount disk’ applies to some thing else. 

That message way that a system going for walks for your Mac has tried to unmount your ordinary boot disk and has failed. In this article, we’ll examine each the ones conditions and the way to solve them.

What does ‘couldn’t unmount disk’ mean?

If you notice an blunders message telling you that macOS couldn’t unmount a disk, it generally way that a system for your Mac is making an attempt to regulate your boot disk and can’t due to the fact macOS won’t permit the disk that it has booted from to be unmounted. 

For example, in case you try and erase or partition your boot disk in Disk Utility, you won’t be capable of due to the fact macOS won’t unmount the disk. Essentially, the erase system has failed for your Mac.

How to restoration ‘couldn’t unmount disk’ blunders

Before you attempt to restoration any trouble with a disk, consisting of one which can’t be unmounted, you must again it up. 

There is usually a danger of dropping facts, and creating a complete backup is the best manner to shield your facts.

The best answer is as well from a unique quantity than the only you’re looking to regulate. On older Macs, meaning booting from an outside disk or USB stick. However, on Macs with T2 protection chips (efficaciously any Intel Mac from the 2018 MacBook Airs, MacBook Pros and Mac minis onwards), and Macs with Apple silicon, it’s now no longer that simple. These Macs have stable boot enabled with the aid of using default, which prevents them from booting from an outside disk. 

You can flip it off the usage of Startup Security Utility, however that’s past the scope of this article. So, on the ones Macs, you must boot from the healing partition with the aid of using doing the following:

Intel Mac


  • Shut down your Mac.
  • Hold down Command-R and strength your Mac on.
  • Release Command-R while you see the Apple logo.

Apple silicon


  • Shut down your Mac.
  • Power for your Mac and hold retaining the strength button till you notice ‘loading startup options’
  • Choose Options, then Continue.
  • Type on your username and password if requested.

You must now see macOS Utilities from wherein you could select Disk Utility after which unmount the quantity from there.

Older Macs

On older Macs that don’t have a T2 protection chip, boot from an outside disk like this:


  • Plug in a disk with a bootable deployation of macOS on it.
  • Click at the Apple menu and select System Preferences.
  • Select Startup Disk.
  • Click the padlock and kind on your admin username and password.
  • Select the disk you’ve simply connected.
  • Quit System Preferences and restart your Mac.
  • When your Mac restarts, release Disk Utility and strive anything you have been looking to do again.

How to restoration it while an outside disk won’t unmount

Normally, while you see the mistake message that an outside disk can’t be ejected, there may be an reason behind why. Usually, there may be an utility going for walks that makes use of the quantity which you’re looking to eject. You have  options:


  • Click on Force Eject. This will override the mistake and eject the disk, however it can additionally harm facts on it.
  • Identify which utility is the usage of the disk and give up it, then attempt to eject the disk again.

How to unmount a disk in Terminal

If not anything else works, you could use Terminal to unmount a disk. You nevertheless won’t be capable of unmount a quantity which you have booted from, however you could use it to unmount an outside disk or from Recovery mode to unmount your major boot disk.


  • Go to Applications > Utilities and release Terminal, or select it from the Utilities menu in macOS Utilities in Recovery mode.
  • Type: diskutil list
  • Press Return.
  • Note the identifier for the disk you need to unmount. For example, ‘disk0s1’
  • Type: sudo diskutil unmountDisk /dev/disks1 [replace ‘disks1’ with the identifier you noted in Step 4.]
  • Press Return and kind on your admin password in case you’re requested for it.

Being not able to unmount a disk for your Mac can look like a terrifying and tough trouble to solve. However, it generally way which you’re looking to unmount your boot disk, which macOS, rightly, won’t permit you to do. Follow the stairs above, and you’ll restoration the trouble fast and be capable of get on together along with your day!


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