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Fix Error “Couldn’t Unmount Disk” in Disk Utility for Mac

"Couldn't Unmount Disk"Disk Utility normally works trouble-free, but an annoying “Couldn’t Unmount Disk” error can also draw up whatever the attempted task is correct in its ways. This can also happen during dividing, disk verification & restore, & even during formatting. And there’s normally too bit to no additional info provided as to a way to fix the issue. Even what the issue is with regards to the error message or the application in Mac OS. In this guide, you will learn the way to Fix the Error “Couldn’t Unmount Disk” in Disk Utility for Mac.

Fix Error “Couldn’t Unmount Disk” in Disk Utility for Mac

Generally the “Couldn’t Unmount Disk” error appears when the recently start drive is being modified. Whether a disk was trying to be removed you probably find the remove the failed with a could not unmount disk error. However, for the former condition where the boot drive is being modified, the simplest fix is to boot from another drive & run Disk Utility from there rather. Just for the boot drive, it should not matter that which version of Mac OS X it is for (assuming 10.7, 10.8, 10.9, 10.10, 10.12, 10.13, 10.14, etc at least), they just need is that it also has the Disk Utility – which they all do.

Similarly, this will permit you to fix the issue, regardless of the purpose, by one of two means, the first is a sure thing to resolve the issue, whilst the other only works occasionally. We will cover both with a little explanation. We will also show you a way to roughly unmount a disk by command line. However, that approach must be used with caution as it also leads to data loss on the drive in query.

Way to fix the Unmount Error with a USB Boot Drive

This is the suggested method just because it should constantly fix the error. However, you guys will also need any Mac OS X boot drive in order to complete this task. Similarly, I used a Mavericks boot installer drive only for this cause. But others should work as well, if they are installation drives or only recovery drives, the essential thing is that they are bootable & also separate from the initial boot disk that saves the installed OS:

  • First of all, attach the USB boot drive to the Mac & restart
  • Here hold down the OPTION key during the start. Choose the attached boot drive (generally has an orange icon at the start menu)
  • At the boot menu, you must have to select “Disk Utility” (whether using an Installer disk, pull down the “Utilities” menu in order to access Disk Utility)
  • Head to the “First Aid” and verify the disk, then repair whether needed
  • Here perform the real task that threw the “Couldn’t Unmount” error

Therefore I ran into this twice currently, first when attempting to modify partitions on a drive. That simply came right along with an individual “partition failed” error. Again it was triggered when attempting to format those partitions. However, the above-mentioned steps did the trick & everything was working again as expected.

This is the perfect instance of why it’s very valuable to have a beneficial USB thumb drive set up with whatever version of Mac OS X is managing on your Macs. Just because without a separate boot drive some of these errors would also be unresolvable. Such boot drives are simple to make on your own, here are tips and tricks for making boot disks for OS X 10.9, OS X 10.8, & OS X 10.7. For ancient Macs running old versions of Mac OS X, generally, anything running OS X 10.6 or earlier will also have a SuperDrive. Therefore shipped with a bootable DVD that is able to also serve this same cause.

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Way to Resolve the Disk Utility Errors through Mac Recovery Partition

Whether the Unable to Unmount Error is activated by first aid or formatting a non-boot partitioning. You probably be able to resolve the error simply by starting from the Recovery partition. That is included with all recent versions of Mac OS X. Similarly, this will not work whether the error was activated. By trying to modify the boot disk via partitions or formatting. And you will then must have to use the process above with a boot disk instead.

  1. Restart the Mac holding down the “Option” key and select the Recovery partition
  2. Choose “Disk Utility” from the boot menu
  3. Head to the “First Aid” to verify & repair the disk, or head to the “Erase” to format the disk

Again, whether the disk throwing the errors is similar to the initial boot partition that Recovery is also on. The above method probably not work to fix the issue. In that situation, you will then must have to start from a separate USB drive to resolve the error.

Read this guide: In Windows or Linux Find Windows Product Key through Command

Way to Forcibly Unmount a Disk by Command Line in Mac OS

Some other method utilizes the command line in order to force unmount a disk. However, this is not the top-suggested option just because of potential for data loss.

Similarly, caution must be used with this approach though. Just because forcibly unmounting a disk can also cause data loss of the drive being forcibly unmounted. Therefore this is only suitable whether you guys plan on formatting & removing the disk to you are forced ejecting anyway.

Simply from the command line of Mac OS, you have to here enter the following string:

diskutil unmountDisk force /Volumes/DRIVENAME

Now replace “DRIVE NAME” with the name of the volume that you guys like to unmount. Next hit the RETURN key in order to force the drive to unmount.

Whether that does not work, so then you can also take this a step further:

You probably also have to target the disk by device identifier just to forcibly unmount it. Similarly, in which case guys can also first find the disk with:

diskutil list

Next, when guys easily find the matching disk to the identifier (/dev/disk1, /dev/disk2, /dev/disk3, etc). You guys are also able to target the disk to unmount as so. Though just for the example syntax here we will use /dev/disk3 to forcibly unmount from command line. Using the sudo which will gain superuser privileges for the task:

sudo diskutil unmountDisk force /dev/disk3

Here hit return & enter the admin password just to forcibly unmount the disk from the Mac.

When completed so then you can also quit out of the Terminal as normal.

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Fix Error “Couldn’t Unmount Disk” in Disk Utility for Mac _ Conclusion

Well, do you guys know of another remedy that can fix the “Couldn’t unmount disk” error message in Disk Utility? So must share your experiences & solutions in the comments section below!

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