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Re: Official way of enabling USB on grub 2.02?

From: adrian15
Subject: Re: Official way of enabling USB on grub 2.02?
Date: Sat, 10 Jan 2015 06:14:02 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.2.0

El 09/01/15 a las 07:10, Andrei Borzenkov escribió:
В Fri, 09 Jan 2015 02:45:40 +0100
adrian15 <address@hidden> пишет:

I'm having problems using my old commands (from grub 2.00) for enabling
USB when using grub 2.02. I also think that in grub 2.00 they did not
work completely ok.

Anyways, the question is:

    How one is supposed to enable Grub2's USB support when using: 2.02?

I'm currently doing my tests with Debian Jessie: 2.02~beta2-19 version.

These were the original commands:
      insmod ohci
      insmod uhci
      insmod usbms

The first one says:
error: disk `hd96' not found

USB drivers work with hardware directly and so conflict with BIOS
for hardware access. For this reasons as soon as you load any driver
that does it grub will stop calling into BIOS. As by default grub is
using BIOS for hard drive access, those devices no more work.
Ok. I can understand it.

But why every command at grub shell (even: echo $grub_prefix) after running: "insmod ohci" always says:

error: disk `hd96' not found.

As I say, this is in grub shell, not running commands from a menu. Although originally I have come to the shell from a menu thanks to 'c' key.

and I cannot longer use my custom grub menues (The Super Grub2 Disk menus).

Thank you for any clue on how to enable USB support in the correct way.

grub2 has command "nativedisk" that will try to switch from platform
firmware driver (BIOS) to native hardware disk drivers. This may give
you back your disks, but under different names. Note that some commands
will not function, e.g. there is no way to chainload something unless
using BIOS.
nativedisk in my virtualbox test also gives me:

error: disk `hd96' not found.

With Grub 2.00-22 (from Debian) I think that USB did not work as I was expecting (just adding a new drive for usb devices detected. I know that you are explaining right now that the current devices are being replaced by new ones. But in 2.00-22 version, at least, I did not give that: error: disk `hd96' not found error.).

Could you give more details what exactly are you trying to do?

As you might imagine what I wanted to achieve in first place is to add usb based devices as grub additional devices so that I can loop between usual grub devices and the usb ones in order to find OSes to boot.

If, as you explain, the cdrom which it's accessed via BIOS is no longer there, then, I guess that I would have to convert (I mean to build it in first place and boot it) the SG2D disk into a memdisk device which I hope it does not get disconnected when "insmod ohci" is run.

And then, well, try to load the usb grub devices.


Given a grub shell, who am I supposed to load usb drives and its devices?

What should it happen when I do it? If there is an usb hard disk. And if there is not?

Can I, somehow, unload or undo the usb drives, without having to reboot?

And how's the best way to keep the original grub device intact? memdisk device?

By the way, we have other commands for enabling raid devices, lvm devices, luks, etc,... and these sort of drives disappearing thing does not happen. Just it helps you.

I'm using Virtualbox 4.3.20 r96996.

Thank you!

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