Grub: Error 21, Selected disk does not exist

Michael msd4824 at
Fri Feb 27 03:46:12 PST 2009

> > 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.



More information about the lfs-support mailing list