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niall_mc Author

Level 1

0 points

Bootcamp partition will not boot

hi there,

I am having an issue with my bootcamp partition on my MacBook.

The windows partition is showing up when I hold down the Option key on startup but it just brings a cursor saying:

A disk Read error occurred.

Press Ctrl+Alt+Del

When I boot into Mac OS X the partition and check Disk Utility the windows partition is greyed out and showing up as disk0s4

From reading other solutions on this site I thought it may be the GPT and the MBr but I am unsure how to fix it.

The results of my fdisk and gpt checks are:

sudo fdisk /dev/disk0

Disk: /dev/disk0 geometry: 60801/255/63 [976773168 sectors]

Signature: 0xAA55

Starting Ending

#: id cyl hd sec - cyl hd sec [ start - size]

------------------------------------------------------------------------

1: EE 0 0 2 - 25 127 14 [ 1 - 409639] <Unknown ID>

2: AF 25 127 15 - 1023 254 63 [ 409640 - 388671872] HFS+

3: AB 1023 254 63 - 1023 254 63 [ 389081512 - 1269536] Darwin Boot

*4: 07 1023 254 63 - 1023 254 63 [ 390352896 - 586420224] HPFS/QNX/AUX

sudo gpt -r -vv show disk0

Password:

gpt show: disk0: mediasize=500107862016; sectorsize=512; blocks=976773168

gpt show: disk0: Suspicious MBR at sector 0

gpt show: disk0: Pri GPT at sector 1

gpt show: disk0: Sec GPT at sector 976773167

start size index contents

0 1 MBR

1 1 Pri GPT header

2 32 Pri GPT table

34 6

40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B

409640 388671872 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

389081512 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC

390351048 1848

390352896 586420224 4 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7

976773120 15

976773135 32 Sec GPT table

976773167 1 Sec GPT header

Any help would be appreciated.

MacBook Pro, Mac OS X (10.7.4)

Posted on Oct 7, 2015 11:11 PM

Best reply

Loner T

Level 9

59,477 points

Posted on Oct 8, 2015 3:26 PM

Please post the output of

sudo dd if=/dev/rdisk0s4 count=1 2>/dev/null | hexdump -C

View in context

61 replies

niall_mc Author

Level 1

0 points

Oct 27, 2015 8:00 PM in response to Loner T

Got the same error as before

Loner T

Level 9

59,477 points

Oct 27, 2015 8:20 PM in response to niall_mc

Press Return only once to go back to the previous screen. We need to check Boot (and compare primary and backup boot), the MFTs. (We may need to continue this tomorrow 😉 ).

Here are some example screens.

niall_mc Author

Level 1

0 points

Oct 27, 2015 8:22 PM in response to Loner T

The boot sector is giving a warning and the backup boot sector is reporting as Bad

Loner T

Level 9

59,477 points

Oct 27, 2015 8:40 PM in response to niall_mc

You are still booted in OS X and are running Testdisk with read-only rights to the disk. Your copy may fail. The safest method is to install Testdisk on a separate disk which is also an OS X Boot disk. If we do that, all your Testdisk windows will be lost.

1. Do you have an external disk? USB flash will be slow, but will work if greater than 16GB.

2. You will need to install Testdisk on the external OS X disk and run the Advanced menu to get back to this point.

3. You will need to decide wether to overwrite the backup BS or not. My recommendation is to do that, but you should also have a good backup of OS X and Windows.

4. You can create an Image Backup of the Bootcamp partition as it exists now, from Testdisk directly.

niall_mc Author

Level 1

0 points

Oct 27, 2015 8:58 PM in response to Loner T

Hi Loner T,

I do have an external drive with a fully bootable OS on it.

Am I correct in saying that you want me to power off the machine and boot up from the external USB drive and then run testdisk on the affected disk - which will probably show up as a different Identifier than rDisk0?

Loner T

Level 9

59,477 points

Oct 28, 2015 3:46 AM in response to niall_mc

Yes, and you will need to install Testdisk on that external boot disk.Because you are booted from the same disk - disk0 - which is also where Windows is, we cannot write to it. Booting from an external allows the internal disk to be written to by Testdisk, if necessary. This may be necessary when we do boot sector updates or rebuild the MFT.

niall_mc Author

Level 1

0 points

Oct 29, 2015 5:12 PM in response to Loner T

Hi Loner T,

Sorry about the delay in getting back to you, really appreciate all your help so far. I was having trouble booting from my bootable backup disk so I had tto create a new one.

I have now launched testdisk from the External drive and have gone to Advanced and the boot option:

Loner T

Level 9

59,477 points

Oct 29, 2015 5:24 PM in response to niall_mc

Did you see any messages about read-only or read-write when you started it on your /dev/rdisk0?

niall_mc Author

Level 1

0 points

Oct 29, 2015 5:33 PM in response to Loner T

There was a warning about not having write access but then I un-mounted the drive in Disk Utility and ran TestDisk again and it did not give any error or warning.