How to restore Windows 7 boot sector from Linux

Question

I have a Laptop dual booting Windows 7 and Ubuntu, however it doesn't boot into Windows anymore. I'm pretty sure the boot sector of the windows partition (the beginning of the partition, not the MBR!) is borked. How do I restore it from Linux?

(The laptop doesn't have a DVD drive, and I'd rather not make a Windows installation USB because it took me several tries last time. Also, the windows installer will overwrite not only the boot sector, but also the MBR, killing GRUB, so I'd have to fix Ubuntu afterwards.)

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Details:

The partition layout is as follows:

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1              54   151129367    75564657    5  Extended
/dev/sda2       151129368   302247179    75558906    7  HPFS/NTFS/exFAT
/dev/sda3   *   302247180   312497351     5125086    c  W95 FAT32 (LBA)
/dev/sda4       312497352   312578243       40446   ef  EFI (FAT-12/16/32)
/dev/sda5             108     4194827     2097360   82  Linux swap / Solaris
/dev/sda6         4194882   151129367    73467243   83  Linux

sda1 is an extended partition containing Linux (sda4, sda5 and sda6). sda3 is the recovery partition (a modified Windows XP, it seems). sda2 is the Windows 7 partition (NTFS). I can mount it from Linux, and everything seems to be there.

Grub can't boot into Windows 7. The boot menu contains an entry called “Windows” (note the funny quotation marks), that tries to boot (hd0,1)=sda1, of course unsuccessfully. I can manually boot sda3, but there's not point to that.

When I try to boot sda2 (Windows 7), I get "NTLDR is missing". This is weird, because Windows 7 doesn't use NTLDR, but BOOTMGR. I don't remember how this got borked up (it happened some time ago), but I guess some recovery tool I tried installed the wrong bootsector on that partition. This is what the beginning of the partition looks like:

$ sudo dd if=/dev/sda2 bs=512 count=1 | hd
00000000  eb 52 90 4e 54 46 53 20  20 20 20 00 02 08 00 00  |.R.NTFS    .....|
00000010  00 00 00 00 00 f8 00 00  36 00 d6 00 18 0d 02 09  |........6.......|
00000020  00 00 00 00 80 00 80 00  f3 df 01 09 00 00 00 00  |................|
[...]
00000170  b4 01 8b f0 ac 3c 00 74  09 b4 0e bb 07 00 cd 10  |.....<.t........|
00000180  eb f2 c3 0d 0a 41 20 64  69 73 6b 20 72 65 61 64  |.....A disk read|
00000190  20 65 72 72 6f 72 20 6f  63 63 75 72 72 65 64 00  | error occurred.|
000001a0  0d 0a 4e 54 4c 44 52 20  69 73 20 6d 69 73 73 69  |..NTLDR is missi|
000001b0  6e 67 00 0d 0a 4e 54 4c  44 52 20 69 73 20 63 6f  |ng...NTLDR is co|
[...]

I have to say I tried update-grub and boot-repair to no avail. Grub is installed and working correctly, what's wrong is the Windows loader that is chainloaded by Grub. What I need is something like bootsect /nt60 C: for Linux, or any way to get a clean copy of the bootloader on to my partition. Any ideas?

Answer 1

Funny how I've been trying this for so long, and just after posting here have found a solution. I've stumbled upon a Windows 7 Recovery USB stick.

1. Boot from the stick. I had to do a cold boot with the stick in an usb port, otherwise the PC wouldn't recognize it. Then I had to tell grub to boot from (hd1).

2. The recovery disk might offer to repair stuff, but that didn't work for me.

3. Start a command prompt and do the following:

   Copy the boot loader over. X: is the recovery drive, C: is the partition on the laptop.

   copy x:\windows\boot\pcat\bootmgr c:\bootmgr
   attrib +s +h c:\bootmgr
   

   If that doesn't work, you might have to remove bootmgr first:

   c:
   attrib -s -h bootmgr
   del bootmgr
   

4. Properly install the boot loader. From X:\windows\system32 call:

   bootsect /nt60 c:
   bootrec /fixboot
   

   The second line is for good measure, not sure it's neccessary. Don't do bootrect /fixmbr, as this will overwrite GRUB.

It could work now, but if it doesn't, you have to recreate the boot menu data (the BCD). From the recovery prompt:

attrib -s -h C:\boot
ren C:\boot C:\bootbak
bootrec /rebuildbcd

Now reboot. Tell grub to boot from (hd0,2) or whatever the windows partition is, and it should work. After a grub-update, Windows 7 should be properly in the menu again.

Resources:

• Info on BOOTMGR that helped me: http://cfc.kizzx2.com/index.php/bootmgr-is-missing-totally-demytisfied/
• How to get a Windows 7 (recovery CD) ISO onto an USB stick: http://www.webupd8.org/2010/10/create-bootable-windows-7-usb-drive.html