Re: Improperly nested partitions, help needed!

[Lennart Sorensen]

On Tue, Sep 21, 2010 at 09:42:14PM +0200, Svante Signell wrote:
> Yes, if I remember correctly, that's what I did some time ago, when
> installing a new disk for /home.
> 
> > If so, then there is a chance that the first sector of sda3 contains
> > the old extended partition table, and grub probe might be detecting that.
> > 
> > One way to check would be to do:
> > 
> > dd if=/dev/sda3 of=/tmp/sda3.mbr bs=512 count=1
> > 
> > Then run 'file /tmp/sda3.mbr'.  If it says partition table, then I think
> > you have found your problem.
> 
> Yes, you are right:
> # file /tmp/sda3.mbr 
> /tmp/sda3.mbr: x86 boot sector; GRand Unified Bootloader, stage1 version
> 0x3, 1st sector stage2 0xdd29b38; partition 1: ID=0x83, starthead 239,
> startsector 63, 35153937 sectors, extended partition table (last)\011,
> code offset 0x48
> 
> # fdisk -lu /dev/sda
> 
> Disk /dev/sda: 160.0 GB, 160041885696 bytes
> 240 heads, 63 sectors/track, 20673 cylinders, total 312581808 sectors
> Units = sectors of 1 * 512 = 512 bytes
> Sector size (logical/physical): 512 bytes / 512 bytes
> I/O size (minimum/optimal): 512 bytes / 512 bytes
> Disk identifier: 0xd568d568
> 
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sda1              63     7575119     3787528+  1b  Hidden W95 FAT32
> /dev/sda2   *     7575120   230640479   111532680    7  HPFS/NTFS
> /dev/sda3       230640480   234541439     1950480   83  Linux
> /dev/sda4       234541440   312575759    39017160    f  W95 Ext'd (LBA)
> /dev/sda5       234541503   240861599     3160048+  83  Linux
> /dev/sda6       240861663   261878399    10508368+  83  Linux
> /dev/sda7       261878463   310413599    24267568+  83  Linux
> /dev/sda8       310413663   312575759     1081048+ 82 Linux swap/Solaris
> 
> > If that is what is happening, then it is a question of whether grub-probe
> > made a mistake when it scanned for partitions in something not marked
> > as a valid place to look for partitions.  Of course the quick workaround
> > in that case is to clear that sector (assuming the filesystem doesn't
> > use the first sector of the partition, which many filesystems avoid
> > since it is a handy place for boot loaders and such).
> 
> You are the Grub developers, you can tell if Grub does the right thing.

I am just a user.

> > If the filesystem does avoid that part of the partition, that would be a
> > good reason an old extended partition table would have survived creating
> > a filesystem.
> 
> So the solution is to blank out the first sector of /dev/sda3,
> 
> dd if=/dev/null of=/tmp/sda3 bs=512 count=1
> 
> to get rid of the warnings? Please confirm the command above is correct.

Not quite.

dd if=/dev/zero of=/tmp/sda3 bs=512 count=1

That should work.  /dev/null is for output.  You need input and a source
of all zeros.

Probably want to save the original you dumped before on some other media
just in case you need to restore it (although I highly doubt it).

-- 
Len Sorensen