Re: Grub 1.99 on external USB disk

[Jordan Uggla]

On Fri, Jun 22, 2012 at 1:50 PM, Nordgren, Bryce L -FS
<address@hidden> wrote:
> Hello,
>
>
>
> I’m trying to get grub 1.99 to boot NixOS from an external USB disk.
> Everything works fine when installed on an internal disk, at least on other
> systems.
>
>
>
> Symptom: System says “welcome to grub”, then “error: prefix is not set”,
> then freezes. No grub rescue prompt. Can’t ctrl-alt-del. Can’t type at all.
> Must power off.
>
>
>
> System (@time of grub-install):
>
> HP2710p laptop
>
> /dev/sda : encrypted internal drive (work)
>
> /dev/sdb: USB flash drive (boot drive) containing NixOS installer
>
> /dev/sdc: 500Gb external USB disk. Two partitions, only /dev/sdc2 is
> relevant (400Gb). The first partition starts at ~1M, leaving room at the
> beginning of the disk. Both partitions are ext3.
>
>
>
> Install command:
>
> grub-install –modules=”ohci uhci usbms ext2” –boot-directory=/mnt/boot
> /dev/sdc

You should pretty much never use the --modules command. If you want
grub to use native drivers, then use "grub-install
--disk-module=native ...".

>
>
>
> Fdisk –l output and grub.cfg are attached. (/dev/sdd is the USB stick used
> to bring these files over to my workstation where I’m writing this email. It
> wasn’t there when grub-install was run.)
>
>
>
> Note that I get a different symptom if the “—modules” option is omitted
> above. It says “welcome to grub”, then “(hd0) out of disk”, then gives me

This indicates that you have a buggy BIOS which can't properly handle
large drives. While having grub use native disk drivers is one
possible way to work around this limitation. you can also try making a
small /boot/ partition near the beginning of the drive.

> the grub rescue prompt. Performing an “ls (hd0,msdos2)/” at the prompt lists
> the first two directories or so, then errors with “(hd0) out of disk”.
> “/boot” is not among the directories listed. Doing “ls (hd0,msdos1)/”
> completes successfully.

That is because the partition starts before your BIOS's limit, and
ends after it. This means that some data (and metadata) will be
readable, and some won't.

>
>
>
> The attached “grub.cfg” attempts to set root and prefix using filesystem
> labels and/or uuid. Neither worked.

$prefix needs to be set properly for the grub.cfg to be read in the first place.

-- 
Jordan Uggla (Jordan_U on irc.freenode.net)