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Re: Possibly erroneous "device not present" message during boot




On Mon 17 Apr 2017 at 08:48:50 +0000, Curt wrote:

> On 2017-04-17, David Wright <deblis@xxxxxxxxxxxxxxxxx> wrote:
> >
> > Oddly, this ancient laptop (Acer) has a slot that makes the SD card
> > look like a /dev/sdX disk, and the BIOS is happy to boot from it.
> 
> I have an Acer X1430 with an internal "Multi-in-1 Media Card Reader" for
> which an SD card inserted into the reader is recognized by the kernel as
> as a /dev/sdX disk.

You have to be careful here to distinguish between what the OS can
recognise and what GRUB can see. The kernel will be using the Multimedia
Card device drivers to detect the device and assign a name to it.  Check
the modules are loaded with

 lsmod | grep mmc

On the other hand, GRUB can only boot from a device when information
is provided to it by the BIOS [1]. Using the normal GRUB setup [2] that
Debian provides, the command

 ls

at the GRUB command prompt (press "c" within the GRUB menu for this)
will show whether a device equivalent to the kernel's /dev/sdX is
discovered.

[1] Not completely correct, but it will do for the point I want to make.

[2] The "normal" setup does not load GRUB's nativedisk module.

-- 
Brian.