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I initially had three bootable partitions:

  • OS X
  • Recovery for OS X
  • Bootcamp (Windows 8)

Now, on Windows, I decided to make my Windows partition smaller, reducing its size using the native Disk Manager. I did, leaving some unallocated space at the end of the disk. Then I restarted my macbook while holding 'alt' and I was surprised to find only one bootable partition:

  • Bootcamp (Windows 8)

Confused, I decided to revert my changes by re-expanding my Windows partition to its original size. The disk mapping looks just the same as before, except I still can't boot on OS X or Recovery for OS X, because they aren't displayed at all on Startup Manager of my macbook.

four partitions on disk

How to fix EFI (or whatever is causing the problem) and boot again on OS X?

[edit: small note, this issue was long time ago... I have reinstalled the whole computer since then]

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3 Answers 3

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Presumably Windows messed up with your OS X boot code. You have to rebuild this code. Since OS X tools can not handle a false flagged partition you have to set the correct partition flag and afterwards rebuild the boot code using OS X Disk Utility.

Since you can't boot from the now unaccessible recovery partition you have to have Linux-tools and a second Mac (accessing your messed up hard disk via target mode 2nd stage) or a OS X install DVD/USB-key by the hand.

Let's go:

Download the latest gParted iso file here: gParted

Burn the iso to a CD or transfer it using the tool of your choice to a USB drive. For help to create a gParted Live-USB look here: Live-USB

Boot your Mac using gParted-Linux.

Go to the gParted-tool. (First window will be opened automagically on the desk.) Select the (probably your first) HFS+ partition and do the right click. Be aware, this is not the first 200 MB EFI-partition!!!

Now edit the partition info.

  • Tick the square for the msft-type.

  • Remove the mark. Do not mark any of the available marks.

  • Write out the changes.

Leave the tool and reboot into a OS X-Install-DVD or prepared OS X install-USB-key (or as forementioned connect your dead Mac-HDD to the other Mac via Firewire or TB now accessing the disk in target mode)

Open OS X Disk Utility.

  • Tick on the Apple HDD, let Disk Utility repair the partition layout.

  • Check the OS X-partition too and reboot into your OS X again.

Hold the alt-key and choose the OS X boot volume. Be happy.

for background stuff from the sources please check search for:

  1. Apple tech notes
  2. steelpangolin

or search for "apple tech notes tn2166" or "steelpangolin invalid-bs_jmpboot-in-boot-block-000000/"

Update:

  1. this is for hdd that has NO hybrid partition only, sorry otherwise this is not for you
  2. please be prepared prior to any further coming desaster

so

  • make a bootable copy of the stock or newly installed OSX (minimum space required ca. 10GB) to an external drive

or

  • create a bootable setup-stick of the setup-image (contained in any OSX Install.app) This will speed up the recovery and makes you more independent from huge downloads esp. over slow lines.
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  • Please specify what you mean with "no hybrid partition"! No hMBR/pMBR or with other words GPT-only?
    – klanomath
    Commented Apr 1, 2015 at 6:03
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May I recommend trying rEFIt? It's a boot loader for EFI partition tables. You can put it on a USB stick and boot from there - it may be able to recognise the OS X partition or otherwise repair your EFI table.

You can download rEFIt here.

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  1. Reboot the Mac into Single User Mode by holding Command+S during boot

  2. At the command prompt, type:

    /sbin/fsck -fy

  3. When fsck is complete, type “exit” or “reboot” to reboot

  4. Boot the Mac as usual, verify the disk again in Disk Utility, and partition as usual

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