Linux Delete / Remove MBR

by nixCraft on August 12, 2011 · 8 comments· LAST UPDATED May 27, 2013

I've installed an usb image on Pen drive along with MBR. Now, I need to use this USB pen for other purpose. Is there a way in Linux to delete the mbr (just like dos fdisk /mbr command)?

You can delete the mbr (master boot recored) using the dd command itself. A master boot record (MBR) is the 512-byte boot sector that is the first sector of a partitioned data storage device of a hard disk.

Understanding MBR size

The mbr size is as follows in bytes:

Tutorial details
Difficulty	Advanced (rss)
Root privileges	Yes
Requirements	dd
Estimated completion time	N/A

Where,446 + 64 + 2 = 512

446 bytes - Bootstrap.
64 bytes - Partition table.
2 bytes - Signature.

Warning examples may crash your computer

WARNING! These examples may crash your computer if executed. The following command will completely delete your MBR including all your partition information. So make sure you use the correct device name and block size in bytes.

Option #1: Command to delete mbr including all partitions

Open a terminal and type the following command command to delete everything:
# dd if=/dev/zero of=/dev/sdc bs=512 count=1
Sample outputs:

1+0 records in
1+0 records out
512 bytes (512 B) copied, 0.00308483 s, 166 kB/s

Where,

if=/dev/zero - Read data from /dev/zero and write it to /dev/sdc.
of=/dev/sdc - /dev/sdc is the USB drive to remove the MBR including all partitions.
bs=512 - Read from /dev/zero and write to /dev/sdc up to 512 BYTES bytes at a time.
count=1 - Copy only 1 BLOCK input blocks.

Option #2: Command to delete mbr only

The following command will erase mbr, but not your partitions:
# dd if=/dev/zero of=/dev/sdc bs=446 count=1
Where,

bs=446 - Read from /dev/zero and write to /dev/sdc up to 446 BYTES bytes at a time.

IIrc, fdisk /mbr does not “delete” your MBR. Instead, it overwrites it with a fresh one. Pasting zeroes on your MBR means it’s no longer a valid boot device (no 55AA signature at the end), it no longer has a bootstrap code on it (typically, it wont say “not bootable partition” if left in a booting computer), and has no structure to welcome new partitions.

Maybe that still does the trick to ensure another tool will not complain that “there is already something installed on this device”, but I remain skeptic over the actual benefit of this step.

2 Jidifi September 16, 2011 at 6:55 am: Sylvainulg,
Linux has a perfect and very easy tool for partitionning anything, fresh devices
without mbr for instance : cfdisk (see: man cfdisk).
Reply

3 angry_user June 23, 2012 at 12:51 pm

This command delete ALL THE DISK, not just MBR. If you have no idea about what are you writing, better STOP writing.
For you fault I’ve lost all my disk. This blog is a shit.

4 AlexC August 27, 2012 at 10:02 pm

I could understand why you are upset. however, you should have read, its pretty clear to me: “The following command will completely delete your MBR, which contains all your partition information….”. BTW, you could have restore your partition. Lastly, there is a link you could have used to delete only the bootstrap part. Don’t get angry after people because you execute command without reading and understanding them first. Again, there is no error in the information provided.

5 Chris February 23, 2013 at 10:13 am

I loll’d

6 nigra May 27, 2013 at 12:50 pm: LOL
Reply

7 creatron October 14, 2012 at 5:08 pm

Indeed the above comments is valid , you could (shall) destroy the partition info, alias everything, leaving many readers in a very unpleasant condition.

dd if=/dev/zero of=/dev/sdc bs=446 count=1
to clear the MBR
and
dd if=/home/dd-mbr.raw of=/dev/sdc bs=446
to restore it from a backup.

Note: To create a backup, one indeed need bs=512, then the partition info is also saved.

Please update the page as this is totally unclear

8 nixCraft May 27, 2013 at 3:57 pm