Question about the dd command

Question about the dd command

[Eric Tchepannou]

Hi all,

I am trying to build a boot image in order to boot from a CD device. I have
already created all the parts ( Kernel, Lilo and Rootfs ) and try to bring
them together. I first copied it on a floppy in order to see wether I could
boot from it and  it worked. In the Linux-Bootdisk-HOWTO It is said that on
should transfer the rootfs with the following command

dd if=rootfs of=/dev/fd0 bs=1k seek=KERNEL_BLOCKS 

I calculated the KERNEL_BLOCK value in my case and applied the command. It
is supposed to transfer the rootfs file into the same floppy containing the
kernel. I am surprised to see that with a ls-command the rootfs.gz is invisible
on the floppy, though the boot process from floppy works properly. Later i
created an image of the floppy ( dd if=/dev/fd0 of=boot.img bs=10k count=144
as in the Linux-Bootdisk-HOWTO ), created an iso file from it with mkisofs and
copied it on CD. Now I can't boot the image from this CD!

I hope I am in the appropriate ML, I hope someone can help me with this
issue,

Regards.

Eric

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Re: Question about the dd command

[jbradford]

Hi,

> I am trying to build a boot image in order to boot from a CD device. I have
> already created all the parts ( Kernel, Lilo and Rootfs ) and try to bring
> them together. I first copied it on a floppy in order to see wether I could
> boot from it and  it worked. In the Linux-Bootdisk-HOWTO It is said that on
> should transfer the rootfs with the following command
> 
> dd if=rootfs of=/dev/fd0 bs=1k seek=KERNEL_BLOCKS 
> 
> I calculated the KERNEL_BLOCK value in my case and applied the command. It
> is supposed to transfer the rootfs file into the same floppy containing the
> kernel. I am surprised to see that with a ls-command the rootfs.gz is invisible
> on the floppy, though the boot process from floppy works properly. Later i
> created an image of the floppy ( dd if=/dev/fd0 of=boot.img bs=10k count=144
> as in the Linux-Bootdisk-HOWTO ), created an iso file from it with mkisofs and
> copied it on CD. Now I can't boot the image from this CD!

I'm assuming that you're trying to create a bootable CD for an X86 machine.

In that case, this is not how bootable CDs work.  You need to look up the 'El-Torito' bootable CD specs, and take it from there.

John.

Re: Question about the dd command

[Bourne]

Eric Tchepannou wrote:
> 
> Hi all,
> 

> dd if=rootfs of=/dev/fd0 bs=1k seek=KERNEL_BLOCKS
> 
I am surprised to see that with a ls-command the rootfs.gz is invisible
> on the floppy, though the boot process from floppy works properly. 

That's Obvious. you do not have a filesystem on /dev/fd0 and hence 'ls'
wont work.

>Later i
> created an image of the floppy ( dd if=/dev/fd0 of=boot.img bs=10k count=144
> as in the Linux-Bootdisk-HOWTO ), created an iso file from it with mkisofs and
> copied it on CD. Now I can't boot the image from this CD!
> 
Try using xcdroast. 

-- 
The art of life is drawing sufficient conclusions from insufficient
premises