GRUB2 Rescue Mode “error: unknown filesystem”

I’ve recently added a second disk to my server, created a single partition /dev/sdb1 and put a ReiserFS filesystem on it. After system reboot I was presented with the grub rescue shell. 

Grub Rescue Shell

That was a bit unexpected, as no GRUB2 related changes were made on the /dev/sda disk that day.

GRUB loading.
Welcome to GRUB!

error: unknown filesystem
Entering rescue mode...

If you get a rescue shell, this usually means that GRUB2 failed to load the “normal” module. Live CDs are good, but a rescue shell is sometimes all we need. Sometimes.

Let’s see what disks and partitions are accessible:

grub rescue> ls
(hd0)(hd0,msdos1)(hd1)(hd1,msdos4)(hd1,msdos3)(hd1,msdos2)(hd1,msdos1)

Since I have just one partition created on the new disk, it must be (hd0,msdos1).

In this case hd1 should be my primary disk. Having figured out that, the rest becomes more of less straightforward. My /boot partition is on (hd1,1), and / is on (hd1,2). Other partitions include /var and swap.

Let’s check if kernel and initrd images are visible:

grub rescue> ls (hd1,1)/
./ ../ lost+found/ System.map-3.2.0-4-686-pae config-3.2.0-4-686-pae grub/ vmlinuz-3.2.0-4-686-pae initrd.img-3.2.0-4-686-pae

Set prefix and root to the correct values and load linux module:

grub rescue> set prefix=(hd1,1)/grub
grub rescue> set root=(hd1,2)
grub rescue> insmod (hd1,1)/grub/linux.mod
grub rescue> normal

Once booted into the OS, I mounted my /boot partition and re-installed GRUB2:

# grub-install /dev/sda
# update-grub

However, after system reboot I was returned to the same rescue grub shell with “unknown filesystem”.

BIOS

It turned out to be a BIOS boot order setting, which was set to boot from the second disk. Having changed the boot order in BIOS, the problem disappeared.

Note to myself: drive ordering in an operating system may not be the same as the boot drive ordering used by a firmware.

35 thoughts on “GRUB2 Rescue Mode “error: unknown filesystem”

  1. I have fedora and Windows 7 what to do ib grub rescue it is showing :-

      Grub loading
    Welcome to GRUB!
    
    Error:unknown filesystem
    entering rescue mode...
    Grub rescue >

    And I followed the same steps given by you but I doesnt works.it shows:-

    Error: hd1 cannot get C/H/S values.
    Grub rescue >
  2. Hey guys I have a little problems.
    First of all sorry for my bad english. And it’s first one. :D
    Lets begin. I had two OS on my laptop /Lenovo G580/ Ubuntu 14.04 and Kali Linux 1.0.8.
    I formatted all sectors were located Ubuntu /in NTFS/.
    My grub was on Ubuntu.
    So…when i reboot laptop i saw the next sentence:

    "error: unknown filesystem
    Entering rescue mode..."
    ls output;
    "(hd0) (hd0,msdos6) (hd0,msdos5) (hd0,msdos4) (hd0,msdos3) (hd0,msdos2)"
    set output:
    cmdpath=(hd0)
    prefix=(hd0,msdos5)/boot/grub
    root=hd0,msdos5"

    I tried to change grub direction to Kali linux file, but it does not work.
    Help me.

  3. not any hd partition works visible….every partition shows “UNKNOWN FILESYSTEM” please tell me what to do now

    • What happens when you try to use the grub rescue mode? Are you able to see your disks and partitions? Can you post the output of ls?

    • hey tom I am also facing same problem .i have installed Ubuntu and windows 8.1….all things were working well last night but today I got this error …have done nothing ;(

      out put is:
      when I presspower button
      error:unknown filesystem
      Entering rescue mode…
      grub rescue > _(and when I type ls)
      (hd0) (hd0,msdos5) (hd0, msdos3) (hdo,msdos2) (hdo, msdos1)
      and grub rescue > ls (hd0)/
      error: unknown filesystem.
      same error with other commands (I installed Ubuntu on same hard drive by formatting a drive partition to Ubuntu related filesystem means not ntfs etc) so help plz what to do now

  4. Boa noite,
    erro: unknown fillesystem.
    Entering rescue mode…
    grub rescue> ls
    (hd0) (hd0,msdos6) (hd0,msdos5) (hd0,msdos3) (hd0,msdos2) hd0,msdos1)
    grub rescue> set
    prefix=(hd0,msdos1)/grub2
    root=hd0,msdos1
    grub rescue

  5. salut;
    error: unknown filesystem debian
    grub rescue> set prefix=(hd0,msdos8)/grub
    grub rescue> set root=(hd0,msdos5)
    grub rescue> insmod (hd0,msdos8)/grub/linux.mod
    error:file not found
    comment faire

  6. Ubuntu 14.04
    error: unknown filesystem
    Entering rescue mode…
    Grub rescue>

    When i do
    grub rescue> ls
    Grub rescue> (hd0) (hd0,msdos1)
    grub rescue> ls (hd1,1)/
    grub rescue> hd1 cannot get C/H/S values.

    Please help me with this.

  7. GRUB loading.
    WELCOME to GRUB!

    error: unknown filesystem.
    Entering rescue mode….
    grub rescue>ls
    grub rescue>(hd0) (hd0,msdos5) (hd0,msdos2) (hd0,msdos1) (hd1) (hd1,msdos1)

    I tried root,prefix command for all partition (hd0,msdos5) (hd0,msdos2) (hd0,msdos1) (hd1,msdos1)
    I still get
    error:unknown filesystem

    Pls provide me solution ..

    THANKS

  8. i have the same problem:
    have a grub rescue> prompt.. ls
    (hd0) (hd0,gpt3) (hd0,gpt2) (hd0,gpt1)
    when i do ls for each, i get “error: unknown filesystem”
    i am running a single boot ubuntu 14.04LTS on a macbook pro.

    thanks for any help that you can provide

    • You’re using GPT, so try the following:

      set prefix="(hd0,gpt1)/boot/grub"
      insmod part_gpt
      insmod linux
      insmod initrd
      boot
  9. I have same Problem. Unknown filesystem Entering rescue mode.. ls (hd0) (hd0,msdos5) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1) (hd1) please help me

  10. Hello
    I had 2 os.. Windows 7and boss linux. I had removed boss now i cannot on my laptop.it aksing me the grub rescue command..whatever i give i shows me the unknown filesystem pls help me..my ls
    (hd0)(hd0,msdos6)(hd0,msdos5)(hd0,msdos2)(hd0,msdos1)

  11. i give ls (hd0,msdos1)
    unknown file system i check all that all could be unknown file system
    what can i do plzz help

  12. Hello. How to solve= error no such partition problem pls?
    ls
    (Hd0)(hd0,msdos5)(hd0,msdos3)(hd0,msdos2)(hd0,msdos1)

  13. Set is cmdpath=(hd0)
    Prefix=(hd0,msdos6)/boot/grub
    Root=hd0,msdos6

    Pls help me to solve the peoblm. Even i could not reinstall another software.

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