[SOLVED]dual boot-Failed to mount real root device

Question

Hello,
Here is my drives partition info:
/dev/sda1       2,949,122,048 3,907,028,991   957,906,944   7 NTFS / exFAT / HPFS
/dev/sda2               2,048   901,117,951   901,115,904  83 Linux
/dev/sda3    *    901,117,952 1,925,115,903 1,023,997,952   f W95 Extended (LBA)
/dev/sda5         901,120,000   901,439,487       319,488  83 Linux
/dev/sda6         901,441,536   905,648,127     4,206,592  82 Linux swap / Solaris
/dev/sda7         905,650,176 1,925,115,903 1,019,465,728  83 Linux
/dev/sda4       1,925,115,904 2,949,122,047 1,024,006,144   7 NTFS / exFAT / HPFS
/dev/sdb1               2,048     2,099,199     2,097,152  83 Linux
/dev/sdb2           2,099,200    53,299,199    51,200,000  83 Linux
/dev/sdb3          53,299,200    73,779,199    20,480,000  83 Linux
/dev/sdb4          73,779,200   224,673,791   150,894,592   7 NTFS / exFAT / HPFS
I installed Opensuse 12.1 on /dev/sda5. It is booting with Grub, working with no problems. The computer boots directly to Grub menu.
THEN, I installed Arch linux (last release) on both sda and sdb following these mounting points:
/dev/sdb1 mounted as /boot  Ext2
/dev/sdb2 mounted as /   BTRFS
/dev/sdb3 mounted as /usr  BTRFS
/dev/sda2 mounted as /home  BTRFS
Intstallation went smooth until the end. Installed the bootloader.
Now, I am trying to configure GRUB to boot Arch.
Here is what I added on /boot/grub/menu.lst, in sda5 under Opensuse:
title Arch Linux  [/boot/vmlinuz-linux]
    root (hd1,0)
    kernel /vmlinuz-linux root=/dev/sdb1 ro
    initrd /initramfs-linux.img
In Opensuse, i can check that vmlinux and grub/menu.lst are indeed in /dev/sdb1
My /etc/fstab is on /dev/sdb2
=============================== sdb2/etc/fstab: ==========
# /etc/fstab: static file system information
# <file system>    <dir>    <type>    <options>    <dump>    <pass>
tmpfs        /tmp    tmpfs    nodev,nosuid    0    0
/dev/sda2 /home btrfs defaults 0 1
/dev/sdb1 /boot ext2 defaults 0 1
/dev/sdb2 / btrfs defaults 0 1
/dev/sdb3 /usr btrfs defaults 0 1
With this parameters, i got an message error when booting Arch:
Mounting /dev/sdb1 on /new_root failed: no such device.
Error : failed to mount the real root device.
So, at busybox prompt, I tried this command line :
ramfs # mount -t ext2 /dev/sdb1
Got an error : Can't read /etc/fstab
I tried too to give a uuid adress to sdb1 in my menu.lst file, but it didn't change anything, so I am sure partition number is correct.
It seems to me in fact that GRUB can't find fstab.
Two questions :
-Would it be better in fact to use only 1 GRUB file for both systems? If yes, shall I keep only the grub config from Opensuse?
-What do I wrong with Arch booting? Why can't I boot Arch?
EDIT :1- just realised there is no BOOT flag in my partiton table on /dev/sdb.
            2- root is on /dev/sdb2, not sdb1.
1-I toggled my first partition bootable using fdisk
2-changed root to point to /dev/sdb2
Now booting into Arch login
Last edited by gabx (2011-11-22 22:33:09)

Answer 1

It was a very simple problem. I used the wrong uuid for my /
Correct entry in 40_custom is:
#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.
menuentry "Arch Linux uuid" {
insmod part_msdos
insmod ext2
search --fs-uuid --no-floppy --set=root 8516fa60-0d45-4f33-b269-817c5290f6cc
linux /vmlinuz26 root=/dev/disk/by-uuid/9f32e668-2548-4ed4-a10b-3fbea66a6d95 ro vga=775
initrd /kernel26.img
Now the boot is working great. Next thing was that my /home and swap was not detected.
That was simply because /etc/fstab was still using /dev/sda etc naming. changing  that to uuid solved that part as well.
To use uuid all the way and of cause the correct one solved everything
/Christer
Last edited by agkbill (2011-07-15 16:00:30)