How do I restore w10 bootloader? dual boot with ubuntu on separate hdd

whatitdo6 said:

@topgundcp
Thanks for clarifying that. Makes sense.

those partition files that I will download from you; I assume I could access those by placing them on a usb stick on another computer, plugging that into this problem computer, and then access/use them when booted up in that tool from post #11?

Yes. You can also save it to the same USB that you use to create the bootable ISO. It is a small file ~19MB.

The UEFI firmware supports two boot modes: UEFI mode and Legacy BIOS mode.

- UEFI mode starts the Windows 10 boot process directly from the EFI system partition of a hard drive. UEFI mode and the GUID Partition Table (GPT) partition style on the hard drive do not use boot sectors and there is no need to set any partition as active. Note that the "bootrec /fixboot" and "bootrec /fixmbr" commands are not needed at all, if the hard drive has a GPT partition style.

- Legacy BIOS mode starts the Windows 10 boot process at the first sector of a hard drive containing the MBR boot code. Legacy BIOS mode uses the Master Boot Record (MBR) partition style.

1. How to fix the Windows 10 bootloader if the hard drive has a GUID Partition Table (GPT) partition style.

On a GPT disk, Windows Setup will create a Recovery partition, an EFI system partition, a Microsoft Reserved partition (won't show in Disk Management) and a primary Windows partition.

   Information

The EFI system partition is a FAT32 formatted partition from where the UEFI firmware launches the UEFI bootloader and application. If the EFI system partition has been corrupted, you can use BCDBoot to recreate the EFI system partition boot files by using new copies of these files from the Windows partition.

bcdboot <source>

Examples:
bcdboot c:\windows
bcdboot d:\windows

BCDBoot Command-Line Options

   Information

How to create an Extensible Firmware Interface (EFI) system partition on a GUID Partition Table (GPT) disk.

create partition efi [size=<n>] [offset=<n>]

size=<n> The size of the partition in megabytes (MB). If no size is given, the partition continues until there is no more free space in the current region.

offset=<n> The offset in kilobytes (KB), at which the partition is created. If no offset is given, the partition is placed in the first disk extent that is large enough to hold it.

Examples:
create partition efi
create partition efi size=100
create partition efi size=260 (for "Advanced Format 4Kn" drives)

UEFI/GPT-based hard drive partitions

Boot from the Windows 10 USB/DVD in UEFI mode (marked UEFI in the boot menu). Press either SHIFT+F10 to bring up the command prompt or at the "Install now" screen click "Repair your computer" > "Troubleshoot" > "Command Prompt".



Option 1 - Recreate the EFI system partition boot files.

diskpart
list volume (note the volume letter where the Windows 10 is installed)
exit

bcdboot c:\windows (if "C" is the volume letter of your Windows 10 partition)

BCDBoot copies the boot files from the Windows 10 partition to the EFI system partition and creates the Boot Configuration Data (BCD) store in the same partition.

If the volume letter is incorrect or if you boot from the Windows 10 USB/DVD in Legacy BIOS mode (not marked UEFI in the boot menu), you will receive the following error message: Failure when attempting to copy boot files.



Option 2 - Format the EFI system partition and add boot files to the EFI system partition.

diskpart
select disk 0
list partition
select partition # (make sure to select the EFI system partition)
format quick fs=fat32
exit

bcdboot c:\windows (if "C" is the volume letter of your Windows 10 partition)



Option 3 - How to delete and recreate the EFI system partition, if you do not have unallocated space.

diskpart
select disk 0
list partition
select partition # (make sure to select the EFI system partition)
delete partition override
create partition efi
format quick fs=fat32
exit

bcdboot c:\windows (if "C" is the volume letter of your Windows 10 partition)



Option 4 - How to delete and recreate the EFI system partition, if you have unallocated space.

Note: If your unallocated space is immediately to the right of the EFI system partition.
- step 3: list partition (check the current size of your EFI system partition)
- step 6: create partition efi size=<n> (the size of the partition in megabytes (MB))

Note: The unit in the offset parameter (offset=<n>) is kilobytes (KB), not megabytes (MB) or gigabytes (GB).
1 MB = 1024 KB - MB to KB Conversion Megabytes to Kilobytes Calculator
1 GB = 1048576 KB - GB to KB Conversion Gigabytes to Kilobytes Calculator
Example: Offset is 451 MB > 451x1024=461824 > create partition efi offset=461824

diskpart
select disk 0
list partition (check the current offset of your EFI system partition)
select partition # (make sure to select the EFI system partition)
delete partition override
create partition efi offset=<n> (you need to use kilobytes (KB) instead of megabytes (MB) or gigabytes (GB))
format quick fs=fat32
exit

bcdboot c:\windows (if "C" is the volume letter of your Windows 10 partition)



2. How to fix the Windows 10 bootloader if the hard drive has a Master Boot Record (MBR) partition style.

On an MBR disk, Windows Setup will create a System Reserved partition and a primary Windows partition.

Boot from the Windows 10 USB/DVD in Legacy BIOS mode (not marked UEFI in the boot menu). Press either SHIFT+F10 to bring up the command prompt or at the "Install now" screen click "Repair your computer" > "Troubleshoot" > "Command Prompt".

bootrec /fixboot (writes a new boot sector to the system partition)
bootrec /fixmbr (writes a MBR to the system partition but does not overwrite the existing partition table)

diskpart
list volume (note the volume letter where the Windows 10 is installed)
exit

bcdboot d:\windows (if "D" is the volume letter of your Windows 10 partition)

BCDBoot copies the boot files from the Windows 10 partition to the system partition (active partition) on the primary hard drive and creates the Boot Configuration Data (BCD) store in the same partition. If the System Reserved partition exists, it is the system partition, if not, the Windows 10 partition is the system partition.

If the volume letter is incorrect or if you boot from the Windows 10 USB/DVD in UEFI mode (marked UEFI in the boot menu), you will receive the following error message: Failure when attempting to copy boot files.



If the System Reserved partition exists
- System Reserved partition (System, Active, Primary Partition)
- Windows OS partition (Boot, Page File, Crash Dump, Primary Partition)

If the System Reserved partition does not exist
- Windows OS partition (System, Boot, Page File, Active, Crash Dump, Primary Partition)

This naming convention is confusing. The "System" partition on a Windows computer is where the files needed to "boot" the computer are located. It is normally the first partition on the first hard drive enumerated by the computer's BIOS. The "Boot" partition of a Windows computer can be located on any other hard drive and contains the files for the Windows operating system.

Note: If you receive the error message "Element not found" when you run the "bootrec /fixboot" command, then you have to first mark the System Reserved partition as active. If the System Reserved partition does not exist, then mark your Windows 10 partition as active. There can be only one active system partition at a time on the primary hard drive.

diskpart
select disk 0
list partition
select partition # (if the System Reserved partition does not exist, then select the Windows 10 partition)
active
exit

If you activate the wrong partition, then use the "inactive" command to de-activate it.

You can check whether the partition is active or not, for example: diskpart > select disk 0 > select partition 1 > detail partition > The output will have: Active: Yes/No.

---

How to use BCDBoot to add or repair the boot menu on a dual-boot PC.
Look at post #3 in this thread: EasyBCD Dual Boot management for Win10 and Win7 on separate drives

For more info about UEFI mode and Legacy BIOS mode.
Look at post #5 in this thread: Cant install Windows 10 because of GPT partition error message

Avocado said:

Boot from the Windows 10 USB/DVD in UEFI mode (marked UEFI in the boot menu).



STEP 1:

- recreate the EFI System partition boot files

bcdboot c:\windows

Attachment 115189

STEP 2: (if the above instructions do not work)

- format the EFI System partition and add boot files to the EFI System partition

diskpart
select disk 0
list partition
select partition # (make sure to select the EFI System partition)
format quick fs=fat32
exit

bcdboot c:\windows

STEP 3: (if the above instructions do not work)

- recreate the EFI System partition and add boot files to the EFI System partition

diskpart
select disk 0
list partition
select partition # (make sure to select the EFI System partition)
delete partition override
create partition efi
format quick fs=fat32
exit

bcdboot c:\windows

THANK YOU. This solved it. I think this was mentioned earlier by you or someone else perhaps but I've messed around with it enough now where I vaguely understood what the commands were doing. I actually had to delete the partition, recreate it, and re write the BCD as you suggested in Step 3.

Shoutout to @topgundcp I'm sure that last method you suggested would have worked too, but now I understand how to do it manually, so I learned something.

Also, thank you @NavyLCDR for your help as well.

I have ONE last question, any SAFE way to remove the old ubuntu EFI entries that are present in my UEFI as boot options?

edit: Nvm, figured it out. For anyone else wanting to know how to remove old EFI boot entries, use "EasyUEFI" it is super easy. Took like 10 seconds after install. I DID have two identical looking EFI's for my samsung ssd, one of them, in the details, showed that it had no file path. I assumed that was my old broken one and deleted it, must have been correct bc my computer boots up perfect.

Thanks!!!