# Make OS X Partition active from Windows

I have recently noticed, that I needed more space on my Bootcamp drive, so I unallocated 10 GiB in macOS using DiskPart. After that I rebooted into Windows and used "MiniTool Partition Wizard" to assign that space to the Windows partition. It rebooted and expanded the partition as I expected, but afterwards I wasn't able to boot into my macOS again. It is cleary still there, but it seems, that I have to set a flag to make it bootable again. Also booting into Recovery Mode doesn't work anymore - it's loading very, very slowly and gets stuck at 100% (I even left my notebook over night).

Does anyone know, how to set this flag using Windows?

• Your first mistake was to let Windows change the partitioning - it really doesn't understand how it's fooled into thinking it's in charge. See apple.stackexchange.com/questions/251860/… – Tetsujin Sep 17 '16 at 14:38
• Please add the versions of Windows and OS X are you using. What is the model/year of your Mac? Booted to Internet Recovery Mode could you run the following Terminal application commands and add the output to your question: diskutil list, gpt -r show /dev/disk0 and fdisk /dev/disk0. – klanomath Sep 17 '16 at 15:33
• @klanomath, Maybe some guidance might be in order, especially how the gathered info is going to get from Internet Recovery Mode to Windows where dieTasse can add it to the post. – user3439894 Sep 17 '16 at 15:37
• OSX doesn't use something like a MBR active/boot flag. The problem is that the tools you used don't understand GPT and/or macOS, destroying it's required layout in the process. The easiest way to fix it is by running disk utility and set the startup disk afterwards, that should fix the partition layout and the efi boot volume. – John Keates Sep 17 '16 at 20:24

I have fixed this issue myself, using a tool called gdisk. I converted the partition table back to GPT. The only problem now is, that i can see the recovery partition from the normal system and i can't really boot to it. No big deal for me, because I can use my mac normally again.

1. Boot to Internet Recovery by holding option-command-r on boot until the globe is shown.
2. In Terminal within Recovery, run the following:

INPUT=$(printf "e 1\nee\n\n1\n\nq\ny") diskutil unmountdisk /dev/disk0 fdisk -e /dev/disk0 <<<"$INPUT"  &>/dev/null


For more information, see the source of the commands and other answers to try in Accidently deleted some small sized partitions when installing Windows. OSX Partition wont boot.