RedHat: VFS: Cannot open root device

From: Cédric Pillonel (cedric.pillonel_at_swisscom.com)
Date: 10/17/05 

Date: Mon, 17 Oct 2005 16:44:47 +0200

I have RedHat 9, kernel 2.4.20-31.9.
I have rebuild the kernel to increase the VMALLOC_RESERVE to 256MB. Here are
the steps I have followed:

make mrproper
cp config-2.4.20-31.1 /usr/src/linux/.config
make oldconfig
make dep
make bzImage
make modules
make modules_install
make install

Now I have a new kernel 2.4.20-31.9custom. When I boot this kernel I get the
following error:

VFS: Cannot open root device "LABEL=/" or 00:00
Please append a correct "root=" boot option
Kernel panic: VFS: Unable to mount root fs on 00:00

I use grub as bootloader. Here is my grub.conf file:

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
# all kernel and initrd paths are relative to /boot/, eg.
# root (hd0,0)
# kernel /vmlinuz-version ro root=/dev/hda3
# initrd /initrd-version.img
#boot=/dev/hda
default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
title Red Hat Linux (2.4.20-31.9custom)
         root (hd0,0)
         kernel /vmlinuz-2.4.20-31.9custom ro root=LABEL=/ hdd=ide-scsi
         initrd /initrd-2.4.20-31.9custom.img
title Red Hat Linux (2.4.20-31.9)
         root (hd0,0)
         kernel /vmlinuz-2.4.20-31.9 ro root=LABEL=/ hdd=ide-scsi
         initrd /initrd-2.4.20-31.9.img

If I change the following line like this (replace root=LABEL=/ with
root=/dev/hdc3):
        kernel /vmlinuz-2.4.20-31.9custom ro root=/dev/hdc3 hdd=ide-scsi

It works!
Why the boot option "root=LABEL=/" works for my kernel 2.4.20-31.9 and not
for my kernel 2.4.20-31.9custom?

Thank you.

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