GRUB2 stuck at rescue console, showing "unknown filesystem" for all partitions

Question

I installed Ubuntu 12.04 on my external USB drive, where I have a 700GB NTFS partition followed by the new 6GB ext4 partition and a swap partition (all primary). The GRUB MBR is also installed to the external hard disk.

Since my BIOS puts the external drive as first disk when booting, I removed my internal hard disk before installation in order to avoid ordering problems.

Now when I boot from the external drive, GRUB is stuck at the rescue console with the error "unknown filesystem".

grub rescue> ls
(hd0) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1)

ls (hd0,<any of them>)/ gives me "unknown filesystem", thus also "insmod normal"

GRUB doesn't seem to be able to read my Linux partition as you can see above?! How can I solve this?

---

Additional info:

bootinfoscript says (this is with the internal drive in again, but that does not make a difference):

Grub2 (v1.99) is installed in the MBR of /dev/sdb and looks at sector 1 of the same hard drive for core.img. core.img is at this location and looks for (,msdos2)/boot/grub on this drive.

sdb1: __________________________________________________________________________

    File system:       ntfs
    Boot sector type:  Windows Vista/7: NTFS
    Boot sector info:  No errors found in the Boot Parameter Block.
    Operating System:  
    Boot files:        

sdb2: __________________________________________________________________________

    File system:       ext4
    Boot sector type:  -
    Boot sector info: 
    Operating System:  Ubuntu 12.04 LTS
    Boot files:        /boot/grub/grub.cfg /etc/fstab /boot/grub/core.img

sdb3: __________________________________________________________________________

    File system:       swap
    Boot sector type:  -
    Boot sector info: 

Solution

I also experienced that issue. But I've found a workaround for this.

My USB drive has first NTFS partition of 430GB (sdg1) followed by Linux partition of 10 GB (sdg2) (all primary). I installed Ubuntu (or afterwards Trisquel) to it and had the same error about unknown filesystem.

It was that grub was unable to "see" Linux partition after such "large" NTFS partition. I don't know the exact limitations of GRUB2, but my 430GB was above it.

Here is the workaround:

1. Install grub to USB HDD with root directory at /dev/sdg1 (NTFS partition). You then will have grub.cfg in /boot/grub/ on that partition.

2. Copy kernel and inirtd image to /boot/ubuntu/ at /dev/sdg1.

3. Change grub.cfg to have root at 'hd0,msdos1' and to load kernel and initrd from /boot/ubuntu/.

Done.

Here is my grub.cfg entry, for example:

menuentry 'Ubuntu' {
    insmod gzio
    insmod part_msdos
    insmod ext2
    set root='hd0,msdos1'
    echo    'Loading Linux'
    linux   /boot/iubuntu/vmlinuz-3.5.0-17-generic root=UUID=erg7659b-ad4c-4f84-9ea0-6e9636768669 ro   quiet splash
    echo    'Loading initial ramdisk ...'
    initrd  /boot/iubuntu/initrd.img-3.5.0-17-generic
}

PS: this workaround won't work with every distro (with ArchBang, for example).

Comments

[Sun Dial]

You will probably find your answer here, this chap (drs305) is an expert on Grub. ubuntuforums.org/search.php?searchid=86421203

[AndiDog]

@SunDial: Thanks for the resource, great tutorials there. But none of them seem to be relevant since GRUB even shows the error for ls (each partition).

[Sun Dial]

OK, is sda your hard drive and sdb the USB??

[AndiDog]

Yes, when I start from the live CD, the internal is /dev/sda and external is /dev/sdb. But when I boot from the external, my bios sets the USB drive as the first disk. That's why I installed with my internal hard drive unplugged. But even if I install Ubuntu with that drive plugged in, same issue...

[AndiDog]

Please refer to this thread on ubuntuforums.org.

[Khurshid Alam]

What would be the root=UUID= in that grub.cfg? sdg1's UUID or sdg2's UUID?