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




On Sat 15 Apr 2017 at 23:21:33 (+0100), Brian wrote:
> On Sat 15 Apr 2017 at 16:30:29 -0500, David Wright wrote:
> 
> > On Sat 15 Apr 2017 at 19:57:32 (+0100), Brian wrote:
> > > On Sat 15 Apr 2017 at 13:08:30 -0500, Richard Owlett wrote:
> > > 
> > > > On 04/15/2017 12:24 PM, Brian wrote:
> > > > >
> > > > >Did you overlook this question? You have said your machine does not
> > > > >offer booting from an SD card. Your answer will be interesting.
> > > > 
> > > > Thought I'd answered it elsewhere.
> > > 
> > > Nope. There has been no mention of booting *directly* *from* the SD card
> > > until this subthread.

I think this was answered in 632231ab-5b9f-f22d-0c92-0207280233e9@xxxxxxxxxxx
which is https://lists.debian.org/debian-user/2017/04/msg00468.html
in the other subthread.

> > > > It's on the menu that exists due to the grub on MBR of /dev/sda .
> > > 
> > > So - the card is in its slot on your machine. You do 'update-grub'.
> > > There is now an entry in GRUB's menu. That is fine. This is what you are
> > > booting from? Your grub.cfg looks similar to what you posted before?
> > > 
> > > If GRUB has been installed to the MBR of the SD card it has absolutely
> > > no bearing on the existence of the entry in GRUB's menu. It may as well
> > > not be there when GRUB on the MBR of /dev/sda constructs its grub.cfg.
> > > 
> > > > There is an fschk error of some sort that flies by too fast.
> > > > Otherwise, runs from SD card.
> > > 
> > > I like "simple"; I'm lost.
> > 
> > One can avoid all this messing about with Grub by just copying a
> > netinst ISO onto the SD card instead of a USB stick.
> > 
> > But then you need, as I've pointed out just now, to insert the
> > SD card into the slot _before_ booting, _and_ entering the CMOS
> > Setup Menu to make sure the device has highest booting priority.
> > (This is irrespective of how you wrote the SD card.)
> 
> Nobody in this thread, apart from the OP, has a Lenovo and an SD card.
> He is in the best position to test and report on this suggestion. Less
> than twenty minutes work.

Frustratingly, I can't test this hypothesis, but I'm getting the
impression that whether a PC can boot¹ directly from an SD card in
the PC's SD slot depends² on how the card eventually appears on
the bus.

AFAICT cards that can boot appear later as:

$ ls -l /dev/disk/by-id/ [edited]
usb-General_Combo_CardMMC_SD_000012345678-0:0 -> ../../sdb
usb-General_Combo_CardMMC_SD_000012345678-0:0-part1 -> ../../sdb1
usb-General_Combo_CardMMC_SD_000012345678-0:0-part2 -> ../../sdb2
$ cat /sys/bus/usb/devices/1-4:1.0/uevent
DEVTYPE=usb_interface
DRIVER=usb-storage
PRODUCT=1025/5d/16b
TYPE=0/0/0
INTERFACE=8/6/80
MODALIAS=usb:v1025p005Dd016Bdc00dsc00dp00ic08isc06ip50in00
$ 

whereas those that can't appear as:

$ ls -l /dev/disk/by-id/
mmc-SE32G_0x0109e2ec -> ../../mmcblk0
mmc-SE32G_0x0109e2ec-part1 -> ../../mmcblk0p1
$ cat /sys/bus/mmc/devices/mmc0\:aaaa/uevent
DRIVER=mmcblk
MMC_TYPE=SD
MMC_NAME=SE32G
MODALIAS=mmc:block
$ 

My guess from this is that the former SD card is connected to the
USB bus whereas the latter is connected to a different bus. The
likely candidate from what I've read is the PCIe bus.

My next guess is that the USB bus (sorry about the tautology) can
be run by the OS-less PC (obviously), whereas the other bus can't.
The trade-off is that a PCIe bus would give a much greater speed.

¹ By boot, I mean read the boot sector from the MBR or PBR of a device.
² vice versa really.

Cheers,
David.