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

That didn't help.

First off... the step 2... says mount the Mac Volume....

Well - the HD is mounted already, so that doesn't seem to apply. If you mean the partition/volume under the HD should be mounted... well... there is no "child" shown under Macintosh HD.

With step 4, when I tried it I got

umount failed for force

Pretty much got stuck at that point

did your mac mini come with SSD installed? if not then you may not have an Apple SSD ability

(attaching an SSD to some 3rd party sata thing that acts like an HD does not necessarily make it an SSD in Apple's view. all i know about that is for iMac 2015 the SSD support is built-in to the motherboard. i guess this depends on many things - how your motherboard and thus apple drivers "see things")

i'm running a mac min 2010 on high sierra have 0 prolems. i'm convince you people are hacking your boxes 🙂 for example: you didn't change the "partition scheme type" (guid or dos) on your startup disk did you? you didn't install (virus checkers, disk copiers, ugh disk encryption yuk, etc) software that hooks in to "extend Sierra ability" (which likely should be un-installed before attempting an OS upgrade incase any of those hooks activate)

unless a drive controller (ie sata board and any drivers to make that work) are broken you should be able to unmount unless the drive is in use. if you have (weird) software running that is using it, you can't unmount it? well you might see if umount -f (force unmount). but i'm guessing that's not the real issue.

there ARE problem reports on installing the NEW FILESYSTEM APFS on HD which is rumored to be corrected in the future. I'm only assuming you all saw that and did not select to try apfs though it was not automatically selected.

A bit of an update....

Between your steps 3&4 I did a "diskutil list" just to make sure I was dealing with the right drive.

Instead of your 4 step I did "distil amount force /dev/disk0s2" (disk0s2 being what's displayed in both the GUI diskutil and the diskutil list response)

That did successfully unmount the drive.

But the diskutil convert /dev/disk0s2 resulted in an error "exiting conversion operations with error code -69888"

That error code is an unmount error (inability to unmount), so it seems the convert option wants to mount and unmount before converting.

Also tried unmounting again and doing the "diskutil repair volume /dev/disk0s2" command. Which chugged along for a few minutes and reported back everything was fine.

So ya - still back at square one, once the volume is dismounted and them mounted again, it doesn't want to dismount unless "force" is used, claiming it's still in use. Which is really weird since... how? I booted from USB so how can it be in use?

Etinin,

Does your procedure wipe the drive and do a 'clean' install? If so, I could do that before - I was running High Sierra from a clean install just fine. I got the unmount error when I tried to do an 'over-the-top' installation. I desire this route because I don't want to lose any data. I did try to use Migration Assistant to restore my files after the 'clean' install, but that never worked. I suspect it wouldn't let me restore from my Time Machine backup because the backup was made from a different OS --> Sierra. But, that's poppycock, right? Why would it care that I created the backup from a previous OS?!

I'm still at a loss...

Joe

Nope... no hacking here...all original equipment.

As for your software argument... anti-virus etc.... doesn't make a whole lotta sense many of us (myself included) are booting from USB.

But... there is some sort of software thing going on - yes... it's not a hardware issue as the Apple Store told me. But my impression, was that it was some Apple software thing, not third party.

Try umounting it again. Since I waited till installation was complete before posting, I forgot I got this error the first time, but umounting and retrying conversion worked for me.

In my case I had to mount because my drive was encrypted, so it couldn’t be automatically mounted.

Hello,

Step 2 may apply if you have an encrypted hard drive.

Please try umount forcing again (repeat steps 4 to 6).

If this solution fails, you may try to repeat it exactly as I did it:

Install normally till you get the installation failed message.

If you left click click some empty spots at the window with the error, you'll get a Mac menu just like in recovery. You'll then be able to open the terminal and run steps from 4 to 6. I did try conversion once with the volume mounted. It failed. I force umounted. And then conversion worked flawlessly.

This error is very irritating, it took me 2 days to be able to boot my Mac again, nothing I found on the internet helped, so I hope this procedure works for you guys as well.

I have the same problem when trying to install High Sierra on a Mac mini with SSD (actually running Sierra). Installation stops with said Message:

MacOS could not be installed on your computer

Unable to unmount volume for repair

Quit the installer to restart your computer and try again.

I repeatedly tried, from internal drive, from external bootable disk, with new Installer. Always the same message as above. I also tried to unmount and do first aid with the SSD, also without success.

There are two things remaining:

1. Apple delivers a new Installer, fixing the above problem?

2. Reformat the SSD, installing High Sierra on the new formatted SSD disk and import a time machine backup.

Is there a change to be successful with Nr. 2?

Was there somebody already successful with Nr. 2 for the given problem?

Or, is there a chance that Apple will release a fixed new installer?

Thanks in advance!

I finally succeeded, very painfully! Here is what I have to share:

There was absolutely no way to unmount my ssd (not with external bootable drive, not with disk utility, not over the recovery system, nothing, ...) except when I ran the mac mini with the ssd in target mode. There I could use the Terminal and do a diskutility unmountDisk force /diskXXX.

The rest was some work with installing and restoring from time machine backup. Now everything is fine.

But I think there is a problem with unmounting some ssd in OS X, I dont know whether it is a problem with OS X or with the ssd?

ttaallff,

I say, "Welcome to the Party!" 🙂 I tried this already, as I mentioned in a previous post. I also could get High Sierra to run this way, but had problems using Migration Assistant to restore from my Time Machine backup. Additionally, I'm running Server software and may end up with some permissions issues if the account IDs change.

Joe

If deleting the installer in Applications > Install macOS High Sierra fails to allow you to download, use Recovery Drive - use second option below:

Recovery Drive Options:

• command R to reinstall the latest macOS that was installed on your Mac, without upgrading to a later version

• option command R to upgrade to the latest macOS that is compatible with your Mac

• shift option command R to reinstall the macOS that came with your Mac, or the version closest to it that is still available

Since you are having so much trouble, instead of downloading and installing on top of your current data, I would advise you clone your drive first. Boot from the clone and erase your internal drive. Run the High Sierra installer and select destination drive as your internal drive, Macintosh HD.

After booting into High Sierra, you can manually bring over your data or use migration. I wouldn't use migration if you haven't done a clean install for a while.

Software used to Clone:

CarbonCopyCloner http://www.bombich.com/download.html (All options are available free for 30 days)

SuperDuper! http://www.shirt-pocket.com/ (Free forever to do an erase and install. Purchased version allows for smart updates and schedules)

Nope. Doesn't work. There's no installer in my Applications folder. Trash is empty. AppStore app only gives option to "Open", and does nothing on click.

Rebooted and AppStore allowed me to re-download.

Power down machine and boot into single user mode, it will have a black screen and white text, this is loading all systems support files + drivers, once all is processed, type. fsck -f (File System Check -Force), once done reboot and try again...see if all is well. ping back once you are able to.

Booted into recovery (Option+Command+R). Still no joy.

Opened terminal, force unmounted disk, then used Disk Utility to do "first aid" - reported no errors.

When attempting to convert to APFS (using Disk Utility), get the following:

com.apple.DiskManagement error -69888

While in Recovery Drive....

Open Terminal....

Check for the exact name of the disk:

sudo diskutil list

(you will see the list of drives/partitions, take note of which one is the one you are trying to unmount/format, should be something like /dev/disk<number>)

Then to force unmount disk:

sudo diskutil unmountDisk force /dev/disk<number>

You should get a response to the success or failure to the unmount command.

If drives fails to unmount...

Check for an fsck process:

ps -ax | grep fsck

and then killed that process:

sudo kill <process number>

When drive is unmounted, force format the disk:

sudo diskutil erasedisk JHFS+ Untitled /dev/disk<number>

Once you have an empty disk formatted a HFS+ Mac OS Extended Journaled, you can select to install High Sierra and it will convert it to APFS