Triple boot: “Missing operating system” on Windows 10 partition after Windows update

Solution 1:

How to Fix the Partition Tables

If you have a 2011 model Mac, then you should be using Hybrid partitioning. From linux, you could enter the following commands to restore hybrid partitioning.

sudo gdisk /dev/sda
t
5
0700
r
h
5
y
07
y
n
w
y

If you computer does not boot, then you may need to rebuild the Windows boot files and data. This would require creating a bootable Windows 10 flash drive.

How to Rebuild the Boot Files and Data

After EFI booting from the Windows 10 flash drive, navigate to where you can open a Command Prompt window or just press the shift+F10 key combination. Enter the command given below to determine the drive letter where windows is installed.

echo list volume | diskpart

Here, I will assume the drive letter is C:. If you have a different drive letter then make the appropriate substitutions. To recreate the boot files and data, enter the commands given below.

bootsect /nt60 c: /mbr
attrib -h -s -r c:\boot\bcd
del c:\boot\bcd
bcdboot c:\windows /s c: /f bios

If you do not have a c:\boot\bcd file, then you will get error messages regarding this file. You can ignore these messages.

Note: Since you are EFI booted from the flash drive and Windows 10 is installed on the internal drive to BIOS boot, the command bootrec /rebuildbcd can not be used.