The_dd_command

THE DD COMMAND

This is one of the more complex Linux commands and actually not really suited for new Linux users. But still I would like to give you a little taste of it.

The dd command copies an amount of data block by block. The most basic syntax is:

CODE

# dd if=xxxxx of=yyyyy bs=zzzzzz

( Where if=xxxxx is the source, of=yyyyy is the target and bs= both read and write zzzzz bytes at a time )
But as you might have guessed, the dd command it is much more than that, it can optionally convert data ( ASCII to EBCDIC ), skip blocks, continue after read errors, change uppercase letters to lowercase, etc, etc. ( type "info dd" in a terminal to get the full list of options )

I will now give you a few examples of what dd can do, but I do urge you to have a look at the links posted below to get more detailed information before you really start experimenting with the dd command.

Copy a hard disk partition to another hard disk:

CODE

# dd if=/dev/hda2 of=/dev/hdb2 bs=4096 conv=notrunc,noerror

Cloning an entire hard disk:

CODE

# dd if=/dev/hda of=/dev/hdb conv=notrunc,noerror

Copy a disk partition to a file on a different partition. ( Do not copy a partition to the same partition ! ):

CODE

# dd if=/dev/hdb2 of=/home/bruno/partition.image bs=4096 conv=notrunc,noerror

Restore a disk partition from an image file:

CODE

# dd if=/home/bruno/partition.image of=/dev/hdb2 bs=4096 conv=notrunc,noerror

Copy MBR only of a hard drive:

CODE

# dd if=/dev/hda of=/home/bruno/MBR.image bs=446 count=1

Reverse:

CODE

# dd if=/home/bruno/MBR.image of=/dev/hda bs=446 count=1

Wipe a hard drive of all data ( you would want to boot from a cd to do this ):

CODE

# dd if=/dev/zero of=/dev/hda conv=notrunc

Make an iso image of a CD:

CODE

# dd if=/dev/hdc of=/home/bruno/TEST.iso bs=2048 conv=notrunc

( CD sectors are 2048 bytes, so this copies sector for sector. )

Copy a floppy disk:

CODE

# dd if=/dev/fd0 of=/home/bruno/floppy.image conv=notrunc

You can back up your MBR ( including partition table ):

CODE

# dd if=/dev/hda of=mbr.bin count=1

Put this on a floppy you make with:

CODE

# dd if=boot.img of=/dev/fd0

Boot from the floppy and restore the MBR:

CODE

# dd if=mbr.bin of=/dev/hda count=1

Again, I urge you to be very careful with the DD command . . . switching if= with of= can have catastrophic results.

An extensive how-to of the dd command can be found here: Learn The DD Command Please read it before you start typing "dd" !!

More info: Codecoffee and here Tuxbrothers ( the second section is in English )

Bruno

-- Apr 22 2007 --