Bug#595458: /usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?). [btrfs]

[Nicolas STRANSKY]

On 09/19/2010 02:13 PM, Alexander Kurtz wrote:

Hi Alexander

> Can you contact me directly via Jabber (kurtz.alex at googlemail.com)
> within the next hour or so? This would make debugging a lot easier!
> 
> If not, could you please (in this order):
> 
>  * check wether you use any sorts of RAID/LVM/CRYPTO etc.

Nothing of this sort.
# ls /proc/mdstat
ls: cannot access /proc/mdstat: No such file or directory
# pvs --all
  PV         VG   Fmt Attr PSize PFree
  /dev/ram0           --      0     0
  /dev/ram1           --      0     0
  /dev/ram10          --      0     0
  /dev/ram11          --      0     0
  /dev/ram12          --      0     0
  /dev/ram13          --      0     0
  /dev/ram14          --      0     0
  /dev/ram15          --      0     0
  /dev/ram2           --      0     0
  /dev/ram3           --      0     0
  /dev/ram4           --      0     0
  /dev/ram5           --      0     0
  /dev/ram6           --      0     0
  /dev/ram7           --      0     0
  /dev/ram8           --      0     0
  /dev/ram9           --      0     0
  /dev/sda1           --      0     0
  /dev/sda3           --      0     0
  /dev/sda4           --      0     0
  /dev/sda5           --      0     0
  /dev/sda6           --      0     0

>  * attach the content of /etc/mtab

Attached.

>  * attach the content of /boot/grub/device.map

Attached.

>  * attach the output of these commands
# ls -l /dev/root
ls: cannot access /dev/root: No such file or directory

# stat /
  File: `/'
  Size: 172       	Blocks: 8          IO Block: 4096   directory
Device: bh/11d	Inode: 256         Links: 1
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2010-09-21 23:08:39.886495112 -0400
Modify: 2010-08-30 23:32:19.579626739 -0400
Change: 2010-08-30 23:32:19.579626739 -0400

# stat /boot/
  File: `/boot/'
  Size: 1024      	Blocks: 2          IO Block: 1024   directory
Device: 803h/2051d	Inode: 2           Links: 4
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2010-09-21 23:09:29.000000000 -0400
Modify: 2010-09-20 22:03:33.000000000 -0400
Change: 2010-09-20 22:03:33.000000000 -0400

>  * swap the first and second line of /etc/fstab (/boot and /) 
>    so that / is before /boot, then reboot and try if update-grub works

Unfortunately that didn't work.

>  * try to regenerate /boot/grub by using
>       mv /boot/grub /boot/grub.backup
>       dpkg-reconfigure grub-pc

It didn't work either :(

>  * As I understand /home is also on btrfs. Does
>       grub-probe --target=device --verbose /home
>    work?

Yes!
# grub-probe --target=device --verbose /home
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
grub-probe: info: the size of hd0 is 625142448.
/dev/sda4

>  * Is your root fs maybe a multi-device btrfs?
>  * Did you use
>       btrfs subvolume set-default
>    or similar to change the default subvolume?

It is not.
# btrfs-show
failed to read /dev/sr0
Label: none  uuid: 37ff5f57-832a-4d11-b638-ae1ad0976667
	Total devices 1 FS bytes used 8.48GB
	devid    1 size 39.06GB used 14.79GB path /dev/sda1

Label: /home  uuid: 31cdf12d-c73d-4bc7-a92b-7e8000bbc1a0
	Total devices 1 FS bytes used 140.64GB
	devid    1 size 210.01GB used 191.79GB path /dev/sda4

Btrfs Btrfs v0.19

>  * Can you try the current squeeze kernel (2.6.32) and see
>    if things work with that?

That DID work!
What could my kernel possibly be missing?

Thanks for your help!

-- 
Nico
GPG FBFA4781



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