Sunday, December 11, 2011

Repair MBR in Windows using mbrfix, fixmbr, bootrec, testdisk, dd and gag

Accidentally rewritten your MBR (or even the partition table) and can't find your old Win9x friend, "fdisk /mbr"? Well, here's a couple of ways on how to fix it:
  • Fixmbr.exe - Repairs the master boot record of the boot disk. The fixmbr command is only available when you are using the Recovery Console. Example: "fixmbr \Device\HardDisk0"
  • Bootrec.exe tool in the Windows Recovery Environment to troubleshoot and repair startup issues in Windows Vista. The /FixMbr option writes a Windows Vista-compatible MBR to the system partition. This option does not overwrite the existing partition table. Use this option when you must resolve MBR corruption issues, or when you have to remove non-standard code from the MBR.
  • MbrFix.exe - Free tool that performs several Master Boot Record (MBR) tasks like backup, restore, rewrite (fix) the boot code in the MBR, etc. Supports Windows NT, Windows 2000, Windows XP, Windows Server 2003, Windows Vista and Windows PE. Both 32-bit and 64-bit x64 edition. Don't use for GUID Partition Table (GPT) disks. Example: "MbrFix /drive 0 fixmbr /vista /yes"
  • TestDisk is a powerful free data recovery softwar designed to help recover lost partitions and/or make non-booting disks bootable again.
  • GAG is an open source graphical boot manager which supports multiple operating systems. The floppy or CD can be used to boot Windows (or any other OS), then use recover tools to recover the MBR.
The MBR resides within the first 446 (0x1BE) bytes , the next 64 bytes are the Partition Table, and the last two bytes in the sector are a signature word for the sector and are always 0x55AA.This means that you can use the "dd" tool to backup, restore or modify your MBR "by hand". Example:

dd if=/dev/YOURDISKHERE of=mymbr bs=446 count=1

Will perform a backup copy that can be later restored using dd :-).

What about Linux or other operating systems? Well, you're probably using GRUB or LiLO, so you can simply boot your partition using (any) LiveCD (or GAG) and restore them. As simple as boot, fsck, mount, chroot, grub - you're set. You can also try using SuperGrubBootDisk.