Questions about the dd command

[Neil]

On Fri, Feb 29, 2008 at 10:24 PM, Karl Larsen <k5di at zianet.com> wrote:
> elmo 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?
>  >
>     There is no point to using dd from a CD-Rom. That is silly.

Even if he is trying to copy the OS? I'd dare to say copying the OS
while that OS is running is a risk at best. If the OS decides to
update something (or do a cron job) your resulting harddisk may have
inconsistencies. Or does Ubuntu protect itself in some strange way?
If I read it correctly he is not trying to do "dd if=/dev/cdrom
of=/dev/sdb2" which would be silly, because the resulting harddisk
would have a iso 9660 file system instead of a filesystem that is
usually found on harddisks.
If he were to copy some other harddisk I'd surely advise him to use
the install version because it's faster.
Please explain why running dd from a cdrom is silly in this case.

Neil


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