hey all,

I'm reading a redhat book and they give an example on how to create a bootdisk and put it on floppy.

dd if=/mnt/cdrom/images/bootdisk.img of=/dev/fd0
mount /dev/fd0 /mnt/floppy
cp ks.cfg /mnt/floppy

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How can they 'dd' the img file onto /dev/fd0 if there is no floppy disk inserted? Could I also 'dd' a file onto /dev/hdc (cdrom) if not cd is inserted?


thanks in advance

It is assumed that a floppy is inserted.

No you can't dd to /dev/hdc because it is a cdrom device which is read only.

ok, the floppy was inserted but was not mounted until the 2nd line.

The dd command can write to the device, so the floppy doesn't need to be mounted.
For example, if you have a 30GB hard disk on your laptop you could created a backup of the hard drive image and save it to a mounted external usb drive. Then if the hard drive goes belly up, you can reverse the process.

dd if=/dev/hda of=/media/usbdrive/hda.img bs=512

This will work even if the drive has partition on it. The image file contains the MBR and the partition table.

dd if=/mnt/cdrom/images/bootdisk.img of=/dev/fd0
The bootdisk.img file contains the image of an entire floppy disk including the filesystem. It might of been created with the mkbootdisk command, or might have been copied from a real floppy disk. The dd command writes this image file to the floppy device. So you can start with a blank disk. The image contains the filesystem, so you don't need to format the disk.

mount /dev/fd0 /mnt/floppy
Now that the floppy image is written, the floppy disk contains a filesystem which can be mounted.

And the last line copies the ks.cfg file to the floppy.
cp ks.cfg /mnt/floppy

Make sure you run "umount /dev/df0" before ejecting the floppy disk. The ks.cfg file may still be written to the cache. Because a floppy is so small, the entire filesystem may be cached to speed things up. You need to umount the floppy to save your changes.

that explains it well, thanks!