Grub: Error 21, Selected disk does not exist

unni krishnan unnikrishnan.a at gmail.com
Fri Mar 6 09:11:29 PST 2009


Hi,

  Usually the command

find /boot/grub/stage1

will give the disk were grub stage1 is present

------------------------------------
grub> find /boot/grub/stage1
 (hd0,1)
 (hd0,2)
 (hd0,7)
------------------------------------

Are you able to get that ?

Also in sda I can see only 4 partitions, so there will not be any (hd0,4)

Like :

------------------------------------------
/dev/sda1 (hd0,0)
/dev/sda2 (hd0,1)
/dev/sda5 (hd0,2)
/dev/sda6 (hd0,3)
------------------------------------------

Is root (hd0,3) is working for you ?

On Fri, Feb 27, 2009 at 5:16 PM, Michael <msd4824 at yahoo.com> wrote:
>
> > > I'm going through Linux From Scratch v6.4, and I'm on Chapter 8.4.  Currently,
> > I'm running Linux completely off of an external hard drive, while I'm also
> > building my Linux From Scatch build onto a seperate partition on that disk.  The
> > laptop already has one hard drive in it, but I'm not really touching it.
> > >
> > > Here's what happens:
> > >
> > > grub> root (hd0,4)
> > >
> > > Error 21: Selected disk does not exist
> > >
> > > As I said, we're on the external hard drive, sda.  I'm not really sure what
> > sda2 is, so I've just sorta been ignoring it.  sda5 is the LFS build, while sda6
> > is the host system.  I'm completely ignoring sdb1.
> >
> > your kernel seems to see the usb-disk first, the builtin disk second.
> > thus after booting you have sdA external and sdB internal.
> >
> > don't assume /dev/sda=(hd0) and /sev/sdb=(hd1)!!
> >
> > simple trick to check how grub maps your drives:
> > in the grub console type "root (hd0," and now the TAB key. grub shows
> > all partitions on hd0. now repeat with "root (hd1,"+TAB to see hd1.
> >
> > compare the output with what you get from "fdisk -l".
> >
> > i guess, you'll see you have to use "root (hd1,4)" to specify your
> > external disk.
> >
> > probably your current kernel has builtin support for IDE/ATA only,
> > loading SATA drivers as modules, but AFTER usb support. thus your
> > external usb disk is recognised first, the SATA second.
> >
> > i'd try to fix that first! it's more conveniant to have builtin before
> > external devices.
> >
> >
> > tobias
>
>
> I've tried the tab thing, and I forgot to mention, it isn't working like it's suppose to.  I type root (hd[tab], and nothing appears, it just bumps me down to the next line.  Same thing happens when I even simply type root ([tab].  It's like it doesn't see any disk on my computer.
>
> As for the external being sda...  When I was running the liveCD, the internal was sda, and the external was sdb.  The only flipped when I installed it to the disk.
>
> Thanks.
>
>
>
>
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--
---------------------
With regards,
Unni

"A candle loses nothing by lighting another candle"



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