I am using a 2010 27" iMac with Mac OS High Sierra and Windows 10 via Bootcamp. Recently, I have had an issue where every Mac update renders the Windows partition unbootable. This means that after every Mac OS update, I need to use Gdisk to fix the hybrid partition table so I can boot Windows again. Unfortunately, this time after I did the repair the Mac partition will no longer boot. Is there a way of fixing the hybrid partition table from Windows so I can get the Mac Partition to boot again, it doesn't show up in the ALT menu on startup and if I try to boot using Refind, the boot process begins but doesn't complete with a crossed out circle on the screen.
When I open Fdisk and run list partition, I get the following:
DISKPART> LIST PARTITION
Partition ### Type Size Offset
------------- ---------------- ------- -------
Partition 1 Primary 1370 GB 512 B
Partition 2 Primary 14 GB 1370 GB
Partition 3 Primary 478 GB 1384 GB
Partition 4 Primary 16 KB 1863 GB
The Mac OS is installed on Partition 1, Partition 3 is the Boot Camp one.
The Mac OS partition still doesn't show up, even if I try to reinstall High Sierra from a USB drive.
Running the commands suggested below gave the following results, sorry for including them as an image, I could not work out how to save them from the USB boot drive.
What is the procedure to try and restore the Mac Partition? I think I will need to use GDisk from the Boot Camp partition. I think I messed up the last time I used GDisk on the Mac to get Windows working again so I want to be careful this time! Windows is working so how can anyone help me use FDisk/GDisk on Windows to restore the partition table to a working state?
Best Answer
The usual request is for the OP to post the output from the commands
gpt -r show /dev/disk0
andfdisk /dev/disk0
. You can enter these commands while booted to macOS Recovery. Normally, you boot to macOS Recovery by turning on your Mac and immediately pressing and holding Command (⌘)-R key combination. Continue holding until you see the Apple logo. Startup is complete when you see an utilities window similar to what is shown below.Once boot to macOS Recovery, you can select to open a Terminal window from the menu bar.
If you can not boot to macOS Recovery and can boot Windows, then you can download and use GPT fdisk to print the contents of the GPT and MBR partition tables. After downloading and extracting, you will need to enter the command
gdisk64 \\.\PhysicalDrive0
from an "Administrator: Command Prompt" window. To print the tables, enter the following when prompted bygdisk64
.After posting the content of these tables to your question, I would hopefully be able to advise on the next step.
Update:
Here are instructions for using
gdisk
under Windows to fix the MBR partition table.Start by entering the command
gdisk64 \\.\PhysicalDrive0
in an "Administrator: Command Prompt" window. Here, I assume the current directory in the window contains thegdisk64.exe
file downloaded from gptfdisk at SourceForge.Below are the commands to enter in to
gdisk
.Below is sample output. Note: Your output might vary slightly from what is shown below.