Code for Concinnity

A couple of years back I blogged about how I solved the frustrating and notorious “BOOTMGR is missing” error in Windows. Today I encountered it again and this time it seems to be more tenacious but I still tamed it after numerous trials. Here I document exactly what went wrong, why it happened and how to solve it.

Background information — how does Windows boot?

Here is a quick rundown. Every step below could possibly go wrong:

1. The BIOS loads the MBR of the booting disk by handing over control to the code residing there. MS’s MBR code will then load the boot sector of the active partition. (If something is wrong here, we need bootsect /nt60 X: /mbr).

2. The boot sector looks for \Boot\BCD and loads boot information from there. The BCD contains where BOOTMGR resides. If this step is wrong, you will see the infamous “BOOTMGR is missing”. To fix this, we need to correct the BCD by bcdedit (see below).

3. Finally BOOTMGR loads winload.exe. If the device or osdevice is set to the wrong partition, Windows may report that winload.exe is corrupt. Normally you fix this by bcdedit. In the rare events that winload.exe is really corrupt, you may need to do a Windows Repair.

Why did it happen?

The base case for this to happen is a multi-hard disk computer. Variations may include changing hard disks after installation, but the principle is the same.

Suppose we have a computer with 2 hard disks:

1. HDD1 (SATA 1/IDE 1)
2. HDD2 (SATA 2/IDE 2)

That is, HDD1 comes before HDD2 in BIOS.

Since Windows cannot determine your boot order from BIOS, it will always configures the MBR in HDD1, and configures the boot sector of the first partition of HDD1 and also put Boot\BCD in the first partition of HDD1. It will always be HDD1, no matter which disk you decide to install Windows on.

Suppose you have the following boot order in BIOS:

1. HDD2
2. HDD1

And suppose you have installed Windows so that:

• HDD1 — bootloader code
• HDD2 — actual Windows installation

Then booting will fail and you will see the notorious BOOTMGR is missing error. Another reason you may see this is that you remove HDD1 after some time, thinking that your Windows installation is nicely contained in HDD2.

Why is Windows Repair not enough?

If you use Winodws repair it will install the boot code in HDD1 and you are forced to adjust the BIOS to boot HDD2 through HDD1. For me, it was a purist’s reason to want to move everything to HDD2.

So here is how exactly I tacked it.

How to fix it

The following steps are assumed to be done in the Windows Recovery environment command line. Boot up your Windows CD and press Shift+F10 to call up the command prompt. We will assume:

• E: to be where Windows is installed.
• F: to be where BCD is set up.
• X: to be the Windows installation CD

1) First, make sure you set the Windows partition as active. You can do this using various partition software or just Google how to do it. Here is an example session using diskpart. You need to replace 99 with the correct numbers:

    > diskpart
    > list disk
    > select disk 99
    > list partition
    > select partition 99
    > active
    > exit

2) Now we gotta make sure the MBR of HDD2 is good to go:

    > cd /d X:\Boot
    > bootsect /nt60 E: /mbr

3) Now migrate BOOTMGR and Boot from F: to E:

    > cd /d F:\
    > attrib -s -e -h bootmgr
    > move bootmgr E:\
    > move Boot E:\
    > cd /d E:\
    > attrib +s +e +h bootmgr

4) Now use bcdedit to fix up the BCD

> cd /d E:\Boot
> bcdedit /store BCD /set {bootmgr} device partition=E:
> bcdedit /store BCD /set {default} device partition=E:
> bcdedit /store BCD /set {default} osdevice partition=E:

5) That’s it!

How to fix it from scratch (what I actually did)

If in the process you think you have screwed up so bad that you want to start over, you don’t have to reinstall Windows:

• It is save to wife out both BOOTMGR and the Boot directory. You can find BOOTMGR in the Windows install CD.

• To recreate the Boot directory, run bootrec /rebuildbcd. Windows will insist on creating it in the first partition in HDD1. You can apply the above techniques to patch up the newly created BCD and then move it to E:. Alternatively you can create BCD from real scratch by using the UUIDs from bcdedit /enum all.

• You should be able to get Windows booted with just the two files E:\BOOTMGR and E:\Boot\BCD. If that worked you will find that Windows boots with Vista style’s green bar. To fix it:

> bcdedit /store E:\Boot\BCD /set {bootmgr} locale en-US
> xcopy /e /h X:\Boot\en-us\ E:\Boot\en-us\

That should be it. Enjoy!