Couldnt unmount disk mac os

I now have a useable disk where before it would not mount and could not be formatted or erased. Running OS X I will be linking this solution to other forums in the future. Excellent post! It worked the 1st time for me, and i also had to stumble across the interweb minefield before finding this solution. Thank you! I did Google your error, and came across this workaround. Do you know what might be causing this?

Fix for disk erase failed couldn’t unmount disk

Your password is being accepted. There are just no dots or asterisks to indicate so. What to do when the problem happens when i am trying to erase the internal hard drive to sell my pac book pro? Try booting into recovery mode holding down Cmd-R during bootup and then erasing it from there. Great tip. This worked great. Took a lot of time to find it but was a flawless solution. Thanks very much. I have been trying off and on for weeks to get rid of this error. I searched high and low and your directions were the easiest to follow and actually worked!!

Thank you very very much. When I try to do this I get an errror on the terminal saying Sudo command unknown… Any ideas? I would suggest copy and paste. Standard accounts do not have enough privileges to escalate using sudo. I was trying to install tacos sierra on my iMac So now i have two broken internal hard drives. Have an external hard drive, which i used to boot up the iMac with el capitan, but i am still in the process of trying to erase the internal drive.

Thank You! Sierra is still beta, right? If the external El Capitan absolutely refuses to unmount the disk, can you try booting into Recovery Mode hold down Cmd-R while booting up and then using Disk Utility there?

Unmounting disk Wiping volume data to prevent future accidental probing failed. Operation failed…. Based on the output you posted, your disk might have unmounted just fine.


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It looks as if the failure came from the wiping part. Thanks so much for the quick and easy tip. Worked like a charm for me to reformat an external drive.

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

Is there a way to work around needing a password? You may be able to rectify this issue by booting into single user mode, and then after the fsck scan renaming the home folder back. You really have to tackle one problem at a time. First, figure out your password.

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

I am trying to format a windows pre-formatted hard drive to use on my mac. Tried to force unmount to no avail. Any idea what else I can do? Thank you. Even after I tried your final option, I got this message:. Went back to disk utilities, erased it this time it did not complain at all , re-installed OS. Very smooth. Thanks a lot. I got same error This lists which process is run on the drive?.

Then use activity monitor to force the process to quite and then redo the partitioning. This resolve my case.

Your Answer

Thanks a lot! It worked! I had a Mac Mini that I needed to reformat and could not get the disk to unmount. So I found this page and tried everything.

macos - Disk Utility won't Unmount HD for formatting - Ask Different

No joy. I was able to force an unmount and could wipe the disk. Same troubles here, just trying to wipe and do a fresh install at this point. You may be able to rectify this issue by booting into single user mode, and then after the fsck scan renaming the home folder back. You really have to tackle one problem at a time.


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  • Disk Utility – Couldn’t unmount disk;

First, figure out your password. I am trying to format a windows pre-formatted hard drive to use on my mac. I watched the video posted here that says to partition it, but my partition button is greyed out, what can I try next? If it successfully unmounts the volumes, the volumes are unmounted and thus should not show up in Finder.

Is there a way to restore the data prior to erasing using the steps above? And what are you trying to do? Get data off the volume before erasing it? Great piece of advice! Worked at first attempt, I was running out of hope after trying several solutions from other forums. Thanks for the post. Yeah, unfortunately, no idea on that. Honestly, since that appears to be an external drive, I would shut down the computer and then just unplug the drive.

Solution Disk Erase Failed with error Couldn't unmount disk mac

I have tried all the methods listed in previous comments. I used to have a boot camp windows 7 that was deleted a year ago If that would effect it. I am not using any external drives.