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?

  • 4
    If I were you, I would make sure I had a Time Machine backup (support.apple.com/kb/ht1427) and erase the entire drive, and then restore from backup. 'Easiest' way to ensure the problem is resolved
    – Josh Hunt
    Commented Mar 12, 2013 at 3:25
  • I agree with @DavidPearce. This shows the dangers of messing with low level elements of your partition scheme if you don't exactly know what you are doing. This is not an area you should be poking into it unless a) you have extensive backups and b) know precisely what you are doing/changing. Trying various tools found on the Internet is not an attractive option here. Use Time Machine and cut your losses. Also, OS X uses GUID and while GPTs have a protected MBR, it's not the same as legacy MBRs.
    – user10355
    Commented Aug 17, 2013 at 17:12
  • I pretty much agree with @DavidPearce as well. What's the output of the following terminal command? diskutil list; echo; diskutil cs list Update the post with it for clarity's sake.
    – njboot
    Commented Jul 2, 2014 at 5:56

2 Answers 2


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.


If you were running Lion or Mountain Lion, you can use rEFInd instead of rEFIt. It's rEFIt refined: http://sourceforge.net/projects/refind/?source=directory

To get back to GUID you'll need a disk with the recovery volume in tact or and install dvd for leopard or lion. You coud also start up from a drive from another mac, anything bootable. Use refind to make it accessible at boot.

Then from the disk utility, you can change it back to guid.

Hope that helps

  • I'll see if this does the trick. When I look at the drive info in Disk Utility it does say it's GUID, Partition Map Scheme : GUID Partition Table
    – nexionly
    Commented Mar 12, 2013 at 15:01

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