High Sierra install fails - "unable to unmount volume for repair"

Hey Andy the link you give does not work, I have a MacBook Pro early 2015 and have completed tried to reformat but when in disk utility I try to first aid it says"unable to unmount volume for repair" I tired everything. I really need help

Hi Andy, so I’ve read thru this thread, and still not grasping this.

I can’t load into OS because it goes straight to the high Sierra install where it wil fail and say restart. So I’m limited to within in recovery mode. I can not do a time machine restore, clean install or anything. Can’t inking the drive. My question is can the commands you got from Apple be used in recover mode in terminal? If so then what. Do I let it restart and do the install or do I stay in recovery and install from there? Appreciate any help from anyone on this

Hi thanks for the reply. I’m aware that is a option. I’d be fine doing a clean install cause backed up the problem with this option is I don’t know how to force homing the drive in terminal in recovery mode. The drive is there and as other people in this thread have had the sand problem but they were able to force it to unmount but I don’t know what I’m doing wrong in terminal. Otherwise I’m not able to erase the drive at all. Even in recovery installing new OS it doesn’t see the drive or to do a time machine restore I can’t skectes my drive. From what people said in this thread it’s something the high Sierra installer screw up with a glitch.

This is so annoying. I still can’t get this thing to unmount. Unmount of disk0 failed: at least one volume could not be unmounted

Can’t do anything. can’t delete my drive, can restore or install in recovery.

Sadly, no joy. Did Andy's suggestion help everyone else here - or are there those who are still stuck, not being able to unmount and erase?

Have dual drives in my 2012 Mac Mini - HDD with Sierra and Server on it (the original start up disk), and a Crucial SSD - installed Sierra on it, and transferred all across.

BOTH drives working as expected - but cannot unmount HDD to erase, and cannot update SSD to High Sierra, on account of both not unmounting.

The suggested Terminal commands (in Terminal on either drives, or in Terminal through Recovery Mode), do not make any difference. Still met with the same error message.

Tried the Internet recovery route as well, and no joy.

That said, I am able to force unmount the drive in Terminal - but since the Installer does not appear to try this, it fails each time.
My concern is that my Mini is the repository of my canonical Photos library - and if I am not mistaken, given the pics that my iPhone 8+ is now taking, it would be preferable if the macOS that my Photos library was being stored on, was running HS...

I might be compelled to nuke and pave everything, upgrade to HS – but then face restoring from a Sierra backup in TM – bit nervous that might give me issues...

Hi - this solution still viable?

Trying to upgrade my new SSD drive to High Sierra (currently sitting on Sierra, as it was transferred over from the original HDD start-up drive using Migration Assistant) - but the installer fails when it tries to erase the drive, since it cannot un-mount it.

The 'force' un-mount command in Terminal does the trick, but since the Installer apparently doesn't try this, it fails.

Would your option possibly work still?

I have this problem on a 2012 i7 Mac Mini with the Apple drive in it and have the same problem. My MBPr 2013 upgraded without issue.

Same problem for me.

Same on my Mac Pro 2013

I have the same problem on:

Currently Running Sierra Version 10.12.6
IMac (Retina 5K, 27-inch, Late 2014)

4 GHz Intel Core i7

Memory 32 GB

Thanks, but this doesn’t work. First Aid from the recovery drive fails to unmount the drive. BUT First Aid from the boot drive sees no errors.

Tried that...

No joy

😟