Cannot boot into Bootcamp after resizing Mac Partition.

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Level 1

11 points

Cannot boot into Bootcamp after resizing Mac Partition.

Hi all,

My Bootcamp has Windows 7 and it is running low with space so I decided to free up an extra 100G from the Mac partition, hoping to merge the 100G to the Bootcamp later.

However, after resizing the Mac part, boot + option, Windows partition would not even show up.

I searched out the previous posts and saw some solutions with command lines. I was wondering if anyone could walk me through the commands and explain a little bit what each line means. I am eager to learn.

Thank you.

P.S. I called Apple and they told me to reconsolidate the 100G back to Mac, but the problem remained.

Posted on Dec 6, 2016 8:06 AM

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Answer 1

Jan 22, 2017 6:19 PM in response to Loner T

Loner T,

You seem to be our resident expert on this. I've read through several of the forums and I seem to be getting stuck at the same place Macnia is.

I have a mid 2012 macbook air running El Capitan. I boot camped it to run windows 7, then upgraded to Win 10 splitting the 500Gb evenly. I found that I eventually needed more space on the windows partition so I used Disk Utility to shrink the Mac partition. After restarting, and holding option, windows no longer appears as a boot option. I do still see boot camp in disk utility.

I tried running the following commands:

sudo fdisk -e /dev/disk0

p

setpid 4

07

flag 4

p

write

y

When I get to the "write" command, I receive "Operation not permitted".

What am I doing wrong?

Thank you in advance

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Answer 2

Loner T

Level 9

59,513 points

Jan 22, 2017 6:31 PM in response to seeteefun

Updating the MBR is not the appropriate solution for your issue. May I suggest a new discussion and post the output of

diskutil list

diskutil cs list

sudo gpt -vv -r show /dev/disk0

sudo fdisk /dev/disk0

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Answer 3

Rudegar

Level 10

173,958 points

Dec 6, 2016 8:19 AM in response to Macnia@PKU

How to fix Bootcamp after partition resize?

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Answer 4

Loner T

Level 9

59,513 points

Dec 6, 2016 8:34 AM in response to Macnia@PKU

If you need more details than the link that Rudegar has posted, please post back, and I can explain the steps and commands in detail.

The process is to find the current GPT and the Hybrid MBR. Resizing only changes the GPT and the resulting mismatch between the two causes the Windows installation not to work and boot. MBRs are allowed only four (4) entries and are limited to 32-bit numbers so cannot address a partition size larger than 2TB and cannot start outside the 2TB boundary.

If you keep the extra partition, then we use MBR stuffing, otherwise if you need to resize and absorb the disk space into Windows then we use GPT Fdisk and GParted to re-map the updated MBR back to a standard four-entry MBR.

The diskutil and gpt/gdisk commands are used to review/manipulate the GPT and MBR. This is valid for legacy BIOS installations of all versions of Windows (W7/W8.1/W10).

In the EFI Boot case, partitioning should be done before you install Windows, to avoid breaking the BCD if the partition is created after the installation.

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