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Guytas avatar Ubuntu

How to prevent DISK from changing MBR to an Hybrid MBR

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Guytas

I had a problem with the EFI partition after I installed Ubuntu on an external drive. I deleted the EFI partition and rebuilt it. Then when I ran boot-repair, it revert back to MBR mode instead of GPT. I changed that using gdisk.

But since then, every time I modify a partition (like increasing its size), DISK updates the MBR (or the boot sector). Not sure how it is supposed to be called. But it sounds like it might think I should be in MBR mode. So it writes the first three partitions to the MBR and it becomes an Hybrid MBR. Windows cannot boot with Hybrid MBR.

I fix this by using gdisk in expert mode to "create a new protective MBR". What I understand, this protective MBR is supposed to tell the software not to update the boot sector with the partitions.

After this, the MBR data look like this

Disk size is 1953525168 sectors (931.5 GiB)
MBR disk identifier: 0x00000000
MBR partitions:

Number  Boot  Start Sector   End Sector   Status      Code
   1                     1   1953525167   primary     0xEE

This is fine but if I change any partition with DISK, it will convert back the MBR into an Hybrid MBR. How can I fix this?

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guiverc avatar
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guiverc
MBR is the first sector the disk (sector 0); called the *Master Boot Record*. It's a standard going back to 1982, with the sector being reserved for that purpose; and sits outside of the Partition Table (be it *legacy* or DOS/MBR or GUID/GPT) as they start at sector 1.
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Super Lite avatar
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Super Lite
Same issue here. This thread is almost a year old and I find many mentions on the internet about the issue but nobody has had success in almost a decade. It still exists in certain circumstances. I have spent 3 days trying to get windows and Ubuntu to play nice together on a GPT disk but Ubuntu keeps breaking the boot capability of windows because it keeps changing the disk to "hybrid mbr." Why would Ubuntu force users to have only hybrid disks.
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