Comments on: UNIX / Linux: Copy Master Boot Record (MBR)

By: Ndoum

Ndoum — Wed, 08 Feb 2012 22:31:51 +0000

I found myself with the MBR on one drive (sda) (which seems to have packed up), Ubuntu 11.04 install (sdb) on another drive and all I have access to is the the 8.04 live disc. I was unable to therefore use things like grub-install since I couldn’t mount my drives (kep getting unrecoginzed file extensions or some such….)

So this seemed the most practical way of doing things since all I wanted to do was create a new MBR where my 11.04 install is with the info from the packed up drive. But a quick check using Boot Info Script:

http://sourceforge.net/projects/bootinfoscript/

shows that core.img is missing from after using dd to replace the MBR on sdb. Mind you I did use 446 since sda is 80Gb and sdb is 160Gb. I assumed I’m dealing with two different sized partitions.

I’d appreciate any insigths…

By: Mike

Mike — Wed, 18 May 2011 15:16:45 +0000

IHi.

I tried this twice to virtualize a physical machine to ESX but each time, on boot, I only have
GRUB _
displayed and no more. I used the 446 bytes size. The partitionning is right and all data have been copied from old to new disk.
I finally startup from a rescue disk, chrooted and used grub-install.

But could grub store data somewhere else ?
(I tried on grub 1 and grub 2 …)

By: Vivek Gite

Vivek Gite — Thu, 17 Mar 2011 17:31:36 +0000

It can be done on both mounted and unmouted file system.

By: Nick

Nick — Thu, 17 Mar 2011 15:58:52 +0000

Hi .. there are numerous info about this nowadays on all sites…
but one thing i never sure of is ….
SHOULD THIS BE DONE ON MOUNTED OR UNMOUNTED FILESYSTEM ????
No sites explain this really…..

By: Vivek Gite

Vivek Gite — Fri, 31 Dec 2010 15:13:54 +0000

Thanks for the heads up!

By: clfapujc

clfapujc — Fri, 31 Dec 2010 10:31:56 +0000

# sfdisk -d /dev/sda > /tmp/sda.bak
# sfdisk /dev/sda < /tmp/sda.out
it should be bak also

By: Niko

Niko — Thu, 02 Dec 2010 15:26:00 +0000

Since this is the first Google result for “linux copy mbr”, please edit original post adding a BIG FAT WARNING about the 512/446 size values.
Thanks

By: Fionn

Fionn — Sun, 21 Nov 2010 00:50:40 +0000

Ash;

If you can use ‘cp’, then you can use ‘dd’; they’re both required for Posix-compliant systems (such as is Debian).

Also, you cannot make a ‘backup’ after the system has crashed. Backups are made before crashes happen so that Recovery may be performed. What you are attempting to do is called ‘salvage’.

By: Ashrock

Ashrock — Mon, 15 Nov 2010 18:52:13 +0000

I am not sure what MBR is until i found this post.
But this is not exactly what i want to do.
I want to copy all the files and directories of a root hard disk with a disk size of 70GB into a external hard drive with a disk capacity of 250GB mounted on /mnt/sda2 .
I can use only cp command as my Debian OS crashed and i want to take immediate backup of all the files.
Is this command useful in any way to do that.
Thanks,

Ash

By: Pavel

Pavel — Mon, 19 Apr 2010 12:31:18 +0000

Very useful comments about 446 bytes. Thanks!

By: Bolo

Bolo — Mon, 21 Dec 2009 20:57:15 +0000

MBR is divided into 3 sections
1. Bootstrap . 446 bytes
2. Partition table. 64 bytes
3. Signature. 2 bytes

By: Brandon

Brandon — Fri, 27 Nov 2009 00:33:29 +0000

MBR is 512 or 446 bytes?

By: Sicarius

Sicarius — Wed, 11 Nov 2009 21:15:04 +0000

Thanks a lot, this was just the kind of short note I was looking for ,)

By: graysky

graysky — Sat, 31 Oct 2009 14:14:36 +0000

Caiken is right! BEWARE of using the above dd line on two discs that don’t have IDENTICALLY sized partitions! You will lose data!

Here’s what I do to copy just the MBR from a hdd:

dd if=/dev/sda of=mbrbackup bs=512 count=1

Now to restore the image to any hdd:

dd if=mbrbackup of=/dev/sdb bs=446 count=1

By: graysky

graysky — Sat, 31 Oct 2009 14:11:51 +0000

Right… be VERY careful with doing this w/ two discs with different size partitions! In fact, the safest way to backup/restore JUST THE MBR:

dd if=/dev/sda of=mbrbackup bs=512 count=1

To restore the MBR (on to the same drive or any drive):

dd if=mbrbackup of=/dev/sdb bs=446 count=1

By: caiken

caiken — Fri, 21 Dec 2007 22:02:16 +0000

This is correct for EXACTLY the same partition sizes. In the case you want the MBR only on a drive that has a root partition of a different size then issue the same command with a smaller block size.

dd if=/dev/sda of=/dev/sdb bs=446 count=1

Thus preserving the partitioning schema.