Grub: Error 21, Selected disk does not exist

Michael msd4824 at yahoo.com
Sun Mar 8 09:52:24 PDT 2009


I tried the following, and it still wouldn't return anything.  After playing around for a bit, I somehow was able to get cd0 and fd0 to appear.  I took a look in the /dev/ folder, and it was pretty much empty.  I'm not sure why I didn't look any sooner.  Running on a laptop, I had to shut down my computer several times during the book when I had to go to work or something.  Apparently, I missed the page when we copied the /dev/ folder from the host system to the build.  Rerunning that command solved all my issues.  Thanks so much for the help!


> 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 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.
> >
> >
> >
> >
> > --
> > http://linuxfromscratch.org/mailman/listinfo/lfs-support
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> 
> 
> 
> --
> ---------------------
> With regards,
> Unni
> 
> "A candle loses nothing by lighting another candle"
> -- 
> http://linuxfromscratch.org/mailman/listinfo/lfs-support
> FAQ: http://www.linuxfromscratch.org/lfs/faq.html
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