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Bliepo 06-16-2009 12:58 PM

LFS will not boot: kernel panic
 
I have recently finished building linux from scratch. However, the system won't boot. I used Ubuntu 9.04 (32 bit) as host and lfsbook version 6.4.

During the boor process, I get this message:
Code:

[  2.186043] VFS: cannot open root device "<NULL>" or unknown-block(8,6)
[  2.186109] Please append a correct "root=" option; here are the availabe partitions:
[  2.186211] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,6)

Because Ubuntu has been installed on an ext4 partition, I use the GRUB that shipped with Ubuntu, because it is able to boot ext4 partitions. My guess is that the error occurs because I am not using the GRUB provided by LFS.

Anyway, here is my menu.lst:
Code:

# menu.lst - See: grub(8), info grub, update-grub(8)
#            grub-install(8), grub-floppy(8),
#            grub-md5-crypt, /usr/share/doc/grub
#            and /usr/share/doc/grub-doc/.

## default num
# Set the default entry to the entry number NUM. Numbering starts from 0, and
# the entry number 0 is the default if the command is not used.
#
# You can specify 'saved' instead of a number. In this case, the default entry
# is the entry saved with the command 'savedefault'.
# WARNING: If you are using dmraid do not use 'savedefault' or your
# array will desync and will not let you boot your system.
default                0

## timeout sec
# Set a timeout, in SEC seconds, before automatically booting the default entry
# (normally the first entry defined).
timeout                10

## hiddenmenu
# Hides the menu by default (press ESC to see the menu)
#hiddenmenu

# Pretty colours
#color cyan/blue white/blue

## password ['--md5'] passwd
# If used in the first section of a menu file, disable all interactive editing
# control (menu entry editor and command-line)  and entries protected by the
# command 'lock'
# e.g. password topsecret
#      password --md5 $1$gLhU0/$aW78kHK1QfV3P2b2znUoe/
# password topsecret

#
# examples
#
# title                Windows 95/98/NT/2000
# root                (hd0,0)
# makeactive
# chainloader        +1
#
# title                Linux
# root                (hd0,1)
# kernel        /vmlinuz root=/dev/hda2 ro
#

#
# Put static boot stanzas before and/or after AUTOMAGIC KERNEL LIST

### BEGIN AUTOMAGIC KERNELS LIST
## lines between the AUTOMAGIC KERNELS LIST markers will be modified
## by the debian update-grub script except for the default options below

## DO NOT UNCOMMENT THEM, Just edit them to your needs

## ## Start Default Options ##
## default kernel options
## default kernel options for automagic boot options
## If you want special options for specific kernels use kopt_x_y_z
## where x.y.z is kernel version. Minor versions can be omitted.
## e.g. kopt=root=/dev/hda1 ro
##      kopt_2_6_8=root=/dev/hdc1 ro
##      kopt_2_6_8_2_686=root=/dev/hdc2 ro
# kopt=root=UUID=b9e51f44-80dc-496b-a669-0e2cb7e79964 ro

## default grub root device
## e.g. groot=(hd0,0)
# groot=b9e51f44-80dc-496b-a669-0e2cb7e79964

## should update-grub create alternative automagic boot options
## e.g. alternative=true
##      alternative=false
# alternative=true

## should update-grub lock alternative automagic boot options
## e.g. lockalternative=true
##      lockalternative=false
# lockalternative=false

## additional options to use with the default boot option, but not with the
## alternatives
## e.g. defoptions=vga=791 resume=/dev/hda5
# defoptions=quiet splash

## should update-grub lock old automagic boot options
## e.g. lockold=false
##      lockold=true
# lockold=false

## Xen hypervisor options to use with the default Xen boot option
# xenhopt=

## Xen Linux kernel options to use with the default Xen boot option
# xenkopt=console=tty0

## altoption boot targets option
## multiple altoptions lines are allowed
## e.g. altoptions=(extra menu suffix) extra boot options
##      altoptions=(recovery) single
# altoptions=(recovery mode) single

## controls how many kernels should be put into the menu.lst
## only counts the first occurence of a kernel, not the
## alternative kernel options
## e.g. howmany=all
##      howmany=7
# howmany=all

## specify if running in Xen domU or have grub detect automatically
## update-grub will ignore non-xen kernels when running in domU and vice versa
## e.g. indomU=detect
##      indomU=true
##      indomU=false
# indomU=detect

## should update-grub create memtest86 boot option
## e.g. memtest86=true
##      memtest86=false
# memtest86=true

## should update-grub adjust the value of the default booted system
## can be true or false
# updatedefaultentry=false

## should update-grub add savedefault to the default options
## can be true or false
# savedefault=false

## ## End Default Options ##

title                Ubuntu 9.04, kernel 2.6.28-11-generic
uuid                b9e51f44-80dc-496b-a669-0e2cb7e79964
kernel                /boot/vmlinuz-2.6.28-11-generic root=UUID=b9e51f44-80dc-496b-a669-0e2cb7e79964 ro quiet splash
initrd                /boot/initrd.img-2.6.28-11-generic
quiet

title                Ubuntu 9.04, kernel 2.6.28-11-generic (recovery mode)
uuid                b9e51f44-80dc-496b-a669-0e2cb7e79964
kernel                /boot/vmlinuz-2.6.28-11-generic root=UUID=b9e51f44-80dc-496b-a669-0e2cb7e79964 ro  single
initrd                /boot/initrd.img-2.6.28-11-generic

title                Ubuntu 9.04, memtest86+
uuid                b9e51f44-80dc-496b-a669-0e2cb7e79964
kernel                /boot/memtest86+.bin
quiet

### END DEBIAN AUTOMAGIC KERNELS LIST

title                Linux from scratch
uuid                ddd93e0b-2ca5-4d49-b7ca-f1a9e1d8f5a0
kernel                /boot/lfskernel-2.6.27.4


# This entry automatically added by the Debian installer for a non-linux OS
# on /dev/sda1
title                Microsoft Windows XP Professional
rootnoverify        (hd0,0)
savedefault
makeactive
chainloader        +1

These are the partitions on my system:
Code:

/dev/sda1 -> ntfs (Windows XP)
/dev/sda2 -> extended
  /dev/sda5 -> ext4 (Ubuntu 9.04)
  /dev/sda6 -> ext3 (LFS)
  /dev/sda7 -> linux-swap

If I need to provide additional information I will be happy to provide it.

vimmex 06-16-2009 02:55 PM

You're not telling grub which partition to mount as root. Add root=/dev/sda6 to the line that starts with kernel, pointing at your lfs partition. You should also re-read the page concerning bootloaders on the LFS book. If you created an initrd, add it there, too.

Just get inspiration from the Ubuntu stanzas in the same file, see what those have and you're missing. And make sure you know what each option means. As far as I can tell, adding the root option should allow you to boot.

jomen 06-16-2009 03:30 PM

adding to that, the line should very probably read:
Code:

kernel /boot/lfskernel-2.6.27.4 root=/dev/sda6
or
Code:

kernel /boot/lfskernel-2.6.27.4 root=UUID=ddd93e0b-2ca5-4d49-b7ca-f1a9e1d8f5a0
provided that the uuid is correct.

You have no separate /boot partition - so you need to copy the lfs-kernel to /boot in Ubuntu like you did - or to copy the Ubuntu kernel(s) to /boot in LFS if you wanted to use its grub installation and configuration instead...


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