IMac 21.5-inch Mid 2010 won’t boot into OS X after installing Ubuntu, will boot into grub rescue

bootcampimacmacosunix

So, as the title says, I have an iMac 21.5-inch Mid 2010 model and I installed Windows 8.1 with Boot Camp. After attempting to uninstall Ubuntu and Windows in Disk Utility (in OS X and Recovery) it would always give me an error,
"Partition failed with the error:
The requested size change for the target disk or a related disk is too small. Please try a different disk or partition, or make a larger change."

What I have tried:

I have tried resetting PRAM/NVRAM with Command + Option/Alt + P+R, nothing.
I have tried holding X to Start up from an OS X startup volume when the Mac would otherwise start up from a non-OS X startup volume. Using Startup key combinations for Mac, still nothing (did work before).
I have done things in grub rescue such as ls (lists partitions and disks) and attempted to boot back into Ubuntu.
I have tried holding Option/Alt to get into the startup manager, still boots to grub rescue.
I have tried holding Command + R to boot into Recovery, worked before, not working now.

What I can't do:

Can't use another Mac to do anything such as target disk mode (no firewire cable).

My iMac Specs:

iMac (21.5-inch, Mid 2010) – Technical Specifications

21.5 inch, 3.06 Mhz, has OSX 10.10 installed with Windows and Ubuntu 14.04.2 LTS.

Best Answer

Fixed after many days. I noticed that the keyboard wasn't initializing during boot so I picked up a new keyboard(something I didn't even think of at the time) and it initialized. I held the Option/Alt key and to prevent this from happening again I installed rEFInd.

Related Solutions

MacOS – Apple recovery partition possibly creating problems in Ubuntu

OS X creates the recovery partition as an alternate boot solution for ease of reinstallation and troubleshooting.

It is not needed for normal operation, and as someone that's familiar with boot technology and options, the simplest option would be to simply delete the partition entirely and patch the partition table if needed.

Here is a stock layout:

Mac:~ me$ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            250.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

You could merge partitions disk0s3 into the partition that precedes it (in this case) to effectively erase and then delete the Apple_Boot partition listed as Recovery HD. In this case, you would need to be booted to some other drive than disk0 to have both disk0s2 and disk0s3 unmountable (which would make them disk1 or higher in all likelihood).

 diskutil mergePartitions JHFS+ "Macintosh HD" disk0s2 disk0s3

Should that not work, you might have to image Macintosh HD to another drive as an img file (or straight partition to partition) and then repartition hdisk0 to have just one partition and restore.

As to the deeper question, my guess is that the "hiding" of the partition isn't compatible with other non Apple tools and is confusing the issue - hence the advice to just remove it and count on alternate options to restore your system or boot externally in stead of the recovery HD.

IMac – How to downgrade a mid-2010 21.5″ iMac from Yosemite to Snow Leopard

Your iMac was delivered with 10.6.6 (somewhat later with 10.6.7). When you have the original (grey) discs that came with it you can use disc 1 to install the Snow Leopard version (not the disc of another machine). Then update it to 10.6.8

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