WARNING: Think twice before applying the latest ML update.

[CountBrass]

Update: If you're having a similar problem, try leaving it on on the grey boot screen overnight (ie several hours). In my case that seemed to resolve the issue. What the issue was remains a mystery.


As I , and others have discovered, the latest ML update completely messes up your hard drive layout to the point that Bootcamp/Windows will not start.

To give you an idea how much it screws things up here is my disk layout *after* the update:

gpt show: disk0: mediasize=751277983744; sectorsize=512; blocks=1467339812
gpt show: disk0: Suspicious MBR at sector 0
gpt show: disk0: Pri GPT at sector 1
gpt show: disk0: Sec GPT at sector 1467339811
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 291015616 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
291425256 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
292694792 1272
292696064 1174642688 4 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
1467338752 1027
1467339779 32 Sec GPT table
1467339811 1 Sec GPT header

</sigh>

Short of completely wiping the disks and starting from scratch (but how without ML disks?!?) I have no idea how I am going to fix Apple's monumental **** up.

Don't they test their damn patches? This one was specifically for the rMBP so it's not as if they have a lot of variations test?

 

[AppleFanatic10]

As I , and others have discovered, the latest ML update completely messes up your hard drive layout to the point that Bootcamp/Windows will not start.

To give you an idea how much it screws things up here is my disk layout *after* the update:

gpt show: disk0: mediasize=751277983744; sectorsize=512; blocks=1467339812
gpt show: disk0: Suspicious MBR at sector 0
gpt show: disk0: Pri GPT at sector 1
gpt show: disk0: Sec GPT at sector 1467339811
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 291015616 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
291425256 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
292694792 1272
292696064 1174642688 4 GPT part - EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
1467338752 1027
1467339779 32 Sec GPT table
1467339811 1 Sec GPT header

</sigh>

Short of completely wiping the disks and starting from scratch (but how without ML disks?!?) I have no idea how I am going to fix Apple's monumental **** up.

Don't they test their damn patches? This one was specifically for the rMBP so it's not as if they have a lot of variations test?

My BootCamp partition boots up fine.

 

[flipnap]

No problems here

 

[\-V-/]

Short of completely wiping the disks and starting from scratch (but how without ML disks?!?) I have no idea how I am going to fix Apple's monumental **** up.

You can make a bootable Mountain Lion installer using a USB flash drive: https://www.macrumors.com/2012/07/25/create-a-bootable-mountain-lion-usb-key-installer/

You just need to download the Mountain Lion installer.

You can also use the recovery partition by holding the alt/option key at boot up.

 

[PhoenixMac]

Mine works fine, and plus one for having backups and a ML USB.

 

[murphychris]

As I , and others have discovered, the latest ML update completely messes up your hard drive layout to the point that Bootcamp/Windows will not start.

Well, having lurked around the Apple forums and hearing about this, I haven't seen a before and after upgrade output of the GPT and MBR, from those having problems. So I don't know what happened to their systems. I've seen hybrid MBRs that have been replaced with PMBRs, but there's no good reason for Apple's installer to do this at all, and obviously most people aren't having the problem. So I don't know what's happening, let alone the trigger for it.

To give you an idea how much it screws things up here is my disk layout *after* the update:

Yeah and, what's the problem? I see four partitions in the usual order: EFI System, Mac OS, Recovery HD, Windows.

Short of completely wiping the disks and starting from scratch (but how without ML disks?!?) I have no idea how I am going to fix Apple's monumental **** up.

Yeah I'm not exactly happy with the lack of a Live CD/DVD image (which could be written to a USB stick as well as burned). This has been standard on linux for many years and it's beyond redonkulous that Apple doesn't do it.

Anyway so long as you can boot Mac OS X, this is repairable there, most likely without starting from scratch. But I can't tell what you think is wrong with the GPT, what your symptoms are, and you also haven't included the hybrid MBR. Please use the following command:

sudo fdisk /dev/disk0

Don't they test their damn patches?

Umm?? Yes. Except yours. They intentionally did this just to you. Is that better?

 

[CountBrass]

So.

I left my machine on over night on the grey boot screen (clutching at straws) and this morning everything works again.

Something strange was going on, no idea what, but simply leaving on the grey boot screen seems to have resolved whatever the issue was.

Weird.

 

[PhoenixMac]

Did you have Bootcamp partition made prior to upgrading to Mountain Lion or after?

 

[murphychris]

So.

I left my machine on over night on the grey boot screen (clutching at straws) and this morning everything works again.

Something strange was going on, no idea what, but simply leaving on the grey boot screen seems to have resolved whatever the issue was.

Weird.

Sounds like possible NVRAM corruption or confusion. I'd zap the PRAM, and reselect the Mac OS and Windows disks in System Preferences > Startup Disk.