UPDATE: This is for a Mac Pro (Mid-2010) MacPro5,1 with the latest firmware, 6-core 3.46 Intel Xeon, 32GB 1333 Mhz DDR3 memory.

I tried the instructions on this post: Triple Boot: “Missing operating system” on Windows 7 partition after Ubuntu installation on my Mac Pro and I’m getting the following at the end of the gdisk commands:

Warning! Main partition table overlaps the first partition by 26 blocks! Try reducing the partition table size by 104 entries. (Use the ‘s’ item on teh experts’ menu.) Aborting write of teh new partition table.

Any suggestions?

I was able to boot into Windows 10 just fine a few weeks ago. I’m not sure what happened in the interim. The only fixpacks I’ve done were on the Windows 10 side. Nothing on the Mac (High Sierra) side.

The Windows disk is a 1 TB SSD with 320GB used for Windows 10 and the other 680GB used for an Apple HFS+ disk.

*************. Edited to provide the info requested: ***************

The disk/partition in question here is disk0 partition 1

diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *1.0 TB     disk0
   1:               Windows_NTFS BOOTCAMP                319.6 GB   disk0s1
   2:                  Apple_HFS 680GB DISK              680.6 GB   disk0s2

/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *960.2 GB   disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:                  Apple_HFS Secondary SSD 1TB       959.9 GB   disk1s2

/dev/disk2 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                 Apple_APFS Container disk4         1000.0 GB  disk2s2

/dev/disk3 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                 Apple_APFS Container disk5         1000.0 GB  disk3s2

/dev/disk4 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1000.0 GB  disk4
                                 Physical Store disk2s2
   1:                APFS Volume OSX Primary HD          509.8 GB   disk4s1
   2:                APFS Volume Preboot                 66.9 MB    disk4s2
   3:                APFS Volume Recovery                1.5 GB     disk4s3
   4:                APFS Volume VM                      20.5 KB    disk4s4

/dev/disk5 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +1000.0 GB  disk5
                                 Physical Store disk3s2
   1:                APFS Volume Mac 1TB Drive           190.4 GB   disk5s1

/dev/disk6 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        +2.0 TB     disk6
   1:                        EFI EFI                     209.7 MB   disk6s1
   2:                  Apple_HFS Time Machine Backups    2.0 TB     disk6s2

sudo gpt -r show /dev/disk0 Password:

       start        size  index  contents
           0           1         MBR
           1           7         
           8   624130252      1  MBR part 7
   624130260        1836         
   624132096  1329389568      2  MBR part 175
  1953521664        3504         

sudo fdisk /dev/disk0 Disk: /dev/disk0 geometry: 121601/255/63 [1953525168 sectors] Signature:

         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
 1: 07 1023 254  63 - 1023 254  63 [         8 -  624130252] HPFS/QNX/AUX
*2: AF 1023 254  63 - 1023 254  63 [ 624132096 - 1329389568] HFS+        
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
  • A 1GB disk is too small...
    – Solar Mike
    Jan 14, 2019 at 4:50
  • You are going to have to post the output from the commands diskutil list, sudo gpt -r show /dev/disk0 and sudo fdisk /dev/disk0. Some of these command may require SIP to be disabled. What is the model/year of your Mac? Do you know if Windows is installed to BIOS or EFI boot? Jan 14, 2019 at 11:15

1 Answer 1


The gdisk command is for editing GUID partition table (GUID_partition_scheme) drives. The drive (disk0) you are referring to is using a Master Boot Record partition table (FDisk_partition_scheme). The command provided by macOS for editing MBR partition table drives is called fdisk.

The current version of gdisk is 1.0.4. If are using the current version, then you would have encountered this message after entering the command.

GPT fdisk (gdisk) version 1.0.4

Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: not present

Found invalid GPT and valid MBR; converting MBR to GPT format
typing 'q' if you don't want to convert your MBR partitions
to GPT format!

Warning! Main partition table overlaps the first partition by 26 blocks!
You will need to delete this partition or resize it in another utility.

You should have interpreted the above message to mean you were using the wrong command.

I am going to assume your Mac Pro is not the 2013 model. I made this assumption because you appear to have installed Windows to BIOS boot.

I can see the first partition on disk0 is not marked as active. This would be a requirement for a BIOS booting windows 10. You would need to make the entries given below to correct this problem. If you get the message fdisk: /dev/disk0: Operation not permitted, then you will need to either disable System Integrity Protection (SIP) or make the entries while booted to Recovery mode.

Note: When using fdisk to display the contents of the MBR partition table, the active (bootable) partition is flagged with the * letter. In your question, you can see that partition 2 is marked as active.

sudo fdisk -e /dev/disk0
flag 1

Below is an example.

Marlin:~ davidanderson$ sudo fdisk -e /dev/disk0
fdisk: could not open MBR file /usr/standalone/i386/boot0: No such file or directory
Enter 'help' for information
fdisk: 1> f 1
Partition 1 marked active.
fdisk:*1> quit
Writing current MBR to disk.
Device could not be accessed exclusively.
A reboot will be needed for changes to take effect. OK? [y] y
Marlin:~ davidanderson$

The me know if you have any questions.

  • It's for a MacPro5,1 (2010) with all of the current firmware updates. And yes, I did get that exact message when I first invoked gdisk. Jan 14, 2019 at 16:50

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