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(grub.info)Device map

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The map between BIOS drives and OS devices
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   When you specify the option `--device-map' (Note: Basic usage),
the grub shell creates the "device map file" automatically unless it
already exists. The file name `/boot/grub/device.map' is preferred.

   If the device map file exists, the grub shell reads it to map BIOS
drives to OS devices. This file consists of lines like this:

     DEVICE FILE

   DEVICE is a drive, which syntax is the same as the one in GRUB
(Note: Device syntax), and FILE is an OS's file, which is normally a
device file.

   The reason why the grub shell gives you the device map file is that
it cannot guess the map between BIOS drives and OS devices correctly in
some environments. For example, if you exchange the boot sequence
between IDE and SCSI in your BIOS, it mistakes the order.

   Thus, edit the file if the grub shell makes a mistake. You can put
any comments in the file if needed, as the grub shell assumes that a
line is just a comment if the first character is `#'.