Failed High Sierra update, can’t mount drives, how to recover files

disk-utilityexternal-diskhigh sierrasoftware-update

The issue is with Apple MacBook Air "Core i5" 1.6 13" (Early 2015).

It had not been backed up in a while but an update to High Sierra was attempted. The update failed and now a regular boot or safe mode boot leads to the "question mark folder". Booting in recovery mode or web-recovery, then attempting to update the OS leads to "Downloading installer information to the target volume failed."

At this point the main concern is to recover the files. In terminal I can see that the files are there, but I can't mount an external drive to copy them. There is power at the USB ports but nothing shows up in Disk Utility ( or "diskutil list").

I made a bootable USB with El Capitan on it, and when I boot from that, the USB ports work. But now the SSD won't mount, so I can't recover anything.
Running "diskutil list" shows the SSD as disk0/disk0s1/disk0s2, but only disk0/disk0s1 can be mounted (of course disk0s2 is the partition I need to access). disk0s2 is APSF, and I don't think its encrypted.

How else can I get one of these disks mounted?

Best Answer

The problem, whatever it was exactly, was solved by having the update completed at an Apple store, connected directly to an update server. Hopefully somebody finds this useful.

Related Solutions

Cannot repair disk0s2 with mavericks utility disk on a SSD

If you have booted from other media and tried Apple's tools then the only thing(s) left are 3rd party tools.

My go-to is Diskwarrior and while some drives with a lot of files will cause it to fail (so I have heard) I've, personally, never had an issue with it. It has always worked and almost always fixed the problem.

Failing that TechTool pro and Prosoft Engineering are a couple of other places to look.

MacOS – Prohibitory sign on boot after Sierra update, can’t mount disk anymore

The Sierra installer messed up with the partition table of disk 1 - probably confused by the custom triple-boot setup and the hybrid MBR on disk1.

Disk1s2 is encrypted with FileVault and got the wrong partition type in the upgrade process somehow.

The partition type of disk1s2 is 48465300-0000-11AA-AA11-00306543ECAC but has to be 53746F72-6167-11AA-AA11-00306543ECAC.

In a TeamViewer session the following was done:

Install wxHexEditor onto "Crucial SSD " to be able to examine the content of disk1
Enable the root user
login as root
examine disk1s2's raw content with wxHexEditor. The type of a volume can be detected by having a closer look at the volume headers and other file system structures (which requires some expertise and/or wikipedia though - examples: HFS+, NTFS).

After removing partition disk1s2 with gpt and re-adding it with the proper type the volume is mountable again:

diskutil list #get all disks and partitions
gpt -r show disk1 #get the partition map of disk1
gpt remove -i 2 disk1
gpt add -i 2 -b 409640 -s 588376248† -t 53746F72-6167-11AA-AA11-00306543ECAC disk1
diskutil verifyDisk disk1

and after unlocking the FileVault volume

diskutil verifyVolume disk2

†: example size

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