unable to mount root fs on unknown--block(0,0)

On Fri, Feb 02, 2007 at 10:14:13AM -0800, Tong Sun wrote:
> Hi,
>
> Does anybody happens to know what might cause this,
> which is what I get when booting my USB disk via grub?
>
> Kernel panic - not syncing: VFS: Unable to mount root
> fs on unknown-block(0,0)
>
> I searched for the answer, but seems most of them
> suggested bad disk, eg,
>
> http://www.mail-archive.com/linux-newbie@vger.kernel.org/msg06843.html
> http://www.linuxforums.org/forum/installation/40167-kernel-panic-not-syncing-vfs-unable-mount-root-fs-unknown-block-8-18-a.html
>
> but my disk fsck fine, mount fine, boot to grub fine,
> just can't mount root. I want to know what other check
> points I should do...
>
> Here is my grub/menu.lst
>
> title GRML Live
> root (hd0,1)
> kernel /boot/vmlinuz
> root=UUID=b53f0a8b-deab-40b3-a84c-0779cb8b7772 ro
> boot
>
> title From grml.live
> root (hd0,1)
> kernel /boot/vmlinuz root=LABEL=grml.live ro
> boot
>
> Note, that although the USB disk is (hd0) during grub
> boot, it will become sdb when Linux starts (tested
> with DSL). would that be an issue?

sure, if the initrd was created without the usb stick then it is
possible that the initrd naming the disks differently and thus can't
find root. watch your boot carefully and see how it names the disks
(scroll-lock helps here).

for example. I was doing some tweaking on my system and had 4 disks
installed.

hda - 4.3 G western digital / partition here on hda3
hdc - 160 G seagate lvm stuff
hde - 160 G seagate lvm stuff
hdg - 160 G seagate lvm stuff

at some point, something changed in the initrd and I got kernel panics
-- can't mount root. I watched the boot and the initrd was assigning
the drives differently so that the drive names were mapped differently

hda --> hde
hdc --> hdg
hde --> hda
hdg --> hdc

so when initrd goes looking for hda3 it points to an lvm partition and
panics. the thing I had to figure out was to get all the disks setup
the way I wanted them at boot and then make a new initrd.

I know its not much help, but might get you down the right path to
solve your problem

hth

A

I ran into this same problem. I'd compiled in all the appropriate modules, so I knew that wasn't the problem. But my USB drive still wasn't listed in the "possible options" list that gets spit out before the kernel panic.

The solution for me was to add rootdelay=10 to my kernel options line. It takes several seconds for my USB drive to initialize. So, it wasn't present by the time the kernel attempted to make it the root device.

The full grub.conf entry:

title=linux usb
root (hd0,0)
kernel /2.6.24-r7/testing/kernel rootdelay=10 root=/dev/sdb2