MacOS – Resetting MBR on iMac

bootbootcampmacospartition

I installed Ubuntu on my iMac (partially successfully) I had rEFIT installed but it did not recognize the Ubuntu installation.

I removed the partition and rEFIT and now when I attempt to install Windows on a new partition created using BootCamp, pressing OPTION does not show the Windows USB created with Boot Camp, nor is the Apple Recovery or whatever partition that was available before.

It seems that my MBR is messed up or something?

I came across OSX86TOOLS and it seems to be able to install EFI and what not, however I'm not certain hat's exactly what I need to do.

Below is from Partition Inspector from rEFIT:

* Report for internal hard disk *

Current GPT partition table: # Start LBA End LBA Type 1
40 409639 EFI System (FAT) 2 409640 624880263 Mac
OS X HFS+

Current MBR partition table: # A Start LBA End LBA Type 1
1 625142447 ee EFI Protective

MBR contents: Boot Code: None

Partition at LBA 40: Boot Code: None (Non-system disk message) File
System: FAT32 Listed in GPT as partition 1, type EFI System (FAT)

Partition at LBA 409640: Boot Code: None File System: HFS Extended
(HFS+) Listed in GPT as partition 2, type Mac OS X HFS+

OSX86TOOLS -> https://code.google.com/p/osx86tools/

Any ideas/advice?

Best Answer

Boot from an install DVD or USB key (If you have one).

From the first installer page choose Disk Utility from the Tools menu.

Check to see if it finds your partition.

Verify/Repair it.

Then, from Tools, choose Startup Disk, and see if you can set your system partition.

If you don't have an install DVD or USB key there are plenty of instructions around on how to do it.

iPartition can change partition schemes without wiping the disk if it comes to that. It's a great tool to have, I've used it a lot for various disk activities over the years, with Linux, Windows, and OSX partitions.

You need a GUID disk to boot OSX normally, not sure how you had it working with an MBR. Disk Utility will normally tell you what you have and how to correct it, if it can.

This is similar: HD accidentally reformatted to MBR, how to get back to GUID?

Long story short - make sure you back up your disk, you're probably going to be reformatting it.

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