Questions about the dd command

Enils ebashi at
Sat Mar 1 05:15:34 UTC 2008

On Fri, Feb 29, 2008 at 11:09 AM, elmo <elmo at> wrote:
> I've spent literally hours trying to find direct answers on the dozens
>  of websites that discuss 'dd'
>  but the couldn't find what I wanted.
>  A few questions about the ' dd ' command:
>   For example:     sudo dd if=/dev/sda2 of=/dev/sdb2 bs=1440
>   1. Which is preferrable;    execute the command from an installed
>        ubuntu (/dev/sda2) or from a ubuntu CD?
>   2. How do you  modify the example  to show the data as it is being
>  copied?

dd will not show you what kind of data it is copying. If it did, it
would look like a bunch of 0s and 1s. All kidding aside, dd does a bit
per bit copy. It does not care what the data looks like.

>      Would this have a drastic effect on how long it takes to complete
>  the copy
>       compared to just watching a blinking cursor?

If you want to see progress instead of a blinking cursor, I would use
"dcfldd". Is pretty much "dd" on steroids. You can run it as follows:

dcfldd if=<source> of=<dest> status=on
Of course you'd have the install it before you use it

>   3.  What effect on the does the ' bs = ' number have on
>       the time to complete the copy or the accuracy of the copy?  Is
>  there a
>       default number if the the bs=    is omitted from the command?
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