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I have a Macbook Pro 2014 with bootcamp partition to Windows 10. I decided to create a partition for data. I created and re-sized the partition in Disk Utility (OSX) but formatted it partition in using Windows, then all the boot options disappeared except for Windows.

The OSX partitions still show up as drives but it no longer shows as a boot option.

Using a ubuntu live disk I was able to get this information:

~$ sudo parted -l
Model: ATA APPLE SSD SM0512 (scsi)
Disk /dev/sda: 500GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt

Number  Start   End    Size   File system  Name                          Flags
 1      20.5kB  210MB  210MB  fat32        EFI System Partition          boot
 2      210MB   141GB  141GB  hfs+         OSX                           msftdata
 3      141GB   142GB  134MB               Microsoft reserved partition
 4      142GB   298GB  156GB  ntfs         NTFS                          msftdata
 5      298GB   298GB  472MB  ntfs                                       hidden, diag
 6      298GB   299GB  650MB  hfs+         Recovery HD                   msftdata
 7      299GB   500GB  201GB  ntfs         Basic data partition          msftdata


Model: Kingston DT 101 G2 (scsi)
Disk /dev/sdc: 7803MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      4129kB  7803MB  7799MB  primary  fat32        boot, lba

How do I get my computer to boot OSX again?

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I suspect your problem is this:

2      210MB   141GB  141GB  hfs+         OSX                           msftdata
6      298GB   299GB  650MB  hfs+         Recovery HD                   msftdata

Both of these HFS+ partitions have the wrong partition type code, which is shown in parted as msftdata. I don't think that parted offers sufficient precision to correct this problem, but gdisk (available in Ubuntu) does. You should change the type code of partition 2 to either AF00 or AF05 (see below) and of partition 6 to AB00. You can use gdisk's t command to make these changes, then type w in gdisk to save the changes to disk.

If you're using a pre-Yosemite version of OS X, the type code for /dev/sda2 should almost certainly be AF00. If you're using Yosemite or later, it could be either AF00 or AF05; the latter is used for OS X's LVM implementation. If you're uncertain, I recommend you try with AF00 and if that doesn't help, try again with AF05.

Incidentally, I don't think you're actually using Boot Camp; I suspect you're booting Windows in EFI mode. Overall this is good, but:

  • Apple's partitioning tools may try to create a hybrid MBR, which will render Windows unbootable. Be wary.
  • Microsoft's partitioning tools will sometimes change the type codes of Apple's partitions. This has already happened to you. Be wary.
  • What do you define Boot Camp to be? Apple reworked the Boot Camp Assistant and the Boot Camp Support Software so most (if not all) Windows 10 installations are done in EFI mode. Furthermore, the newest Macs can install Windows 10 directly from the iso. The these cases there is no need for a DVD for USB flash drive. Older Mac's can install Windows 10 in MBR mode, but this type of installation to not supported by Apple. For example, my 2007 iMac runs 64 bit Windows 10 Pro just fine. (And it was free!) – David Anderson Oct 15 '15 at 18:17

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