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I'm trying to fix the MBR using Ubuntu live CD. I already have the ms-sys installed but from the threads that I saw, I'm not completely sure in which /dev I should execute the command:

sudo ms-sys --mbr7 /dev/???

(is it mbr7 the correct option when using Windows 7?)

ubuntu@ubuntu:~$ sudo fdisk -l

Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x1f205b1f

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          38          38           0    0  Empty
/dev/sda2   *        2048      206847      102400    7  HPFS/NTFS/exFAT
/dev/sda3          206848   155854847    77824000    7  HPFS/NTFS/exFAT
/dev/sda4       155854848   625137663   234641408    7  HPFS/NTFS/exFAT
ubuntu@ubuntu:~$ 

Why is /dev/sda1 empty?

I'm trying to fix the MBR because I'm getting a black screen when trying to load the operating system.

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3 Answers 3

First, your partition table appears to have two active partitions, which may prevent your computer from booting even if you fix the problem of the MBR.

Windows's MBR boot is kind of funky because it uses a "default" MBR to load the MBR of the active partition. Before you change the boot records, try unmarking one of the partitions and booting.

If that doesn't work, the package mbr may be worth looking into. It is able to install the "default" MBR to your disk, which just loads the boot code from the active partition.

As per your question, read/follow these bullet points at your own risk. This stuff has the ability to mess up your partition table. Back it up using dd if=/dev/sda of=table.bin bs=512 count=1 first. I would also recommend backing up all your files. If I understand the docs correctly, doing these commands without -w may prevent them from writing anything without additional user intervention.

  • ms-sys /dev/sda will inspect the hard dist partitions
  • Please read the documentation here. From what I gather, ms-sys can be quite dangerous and is designed to obliterate your entire MBR along with the partition table in several situations. It would seem you are using the wrong utility for the job.
  • ms-sys --ntfs /dev/sdaX where sdaX is your partition with Windows 7 on it. This might do what you are expecting, but probably not.

I think you have the wrong utility for the job here. This does not "fix" MBR's, it destroys and creates them. You may get lucky and have the new partition table line up with the new one, but I wouldn't count on it. Try booting a grub CD and typing chainloader (hd0,<win7 partition>)+1 at the prompt and seeing if it boots. This will help diagnose where your problem is. If else fails, use your windows installation dist to fix the MBR.

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To restore the MBR, the accepted method is to use a Windows CD. We didn’t have that luxury. Fortunately we had a Ubuntu Live USB in hand.

The method to fix the MBR is:

  1. Boot the machine using the Live USB/CD.
  2. Install lilo sudo apt-get install lilo
  3. Fix the MBR using lilo using the command: sudo lilo -M /dev/sda mbr

Works like a charm!

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Here are the two solutions that have have worked for me.

Boot Linux and make sure you’ve a working Internet connection and type the following on the terminal.

1. Solution

sudo apt-get install syslinux

If the package got installed, use the following command to write the MBR:

sudo dd if=/usr/lib/syslinux/mbr.bin of=/dev/sda

2. Solution

sudo apt-get install mbr

If the package got installed use following to write the MBR.

sudo install-mbr -i n -p D -t 0 /dev/sda

Common for both

Replace sda if you want to install the MBR to a different drive. Do not put sda1,sda2, or sda3. Just put it as sda for the hard disk. Finally reboot and your Windows should boot.

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