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I'd successfully installed Ubuntu 10.04.03 LTS with parallel to existing Window 7 Professional. Both the OSes were booting properly without any problem. After install I needed to do sudo update-grub to be able to get grub loader choices.

My HDD partitioning was as below (before the problem):

System partition (105 MB approx.)
C:\
D:\
Ubuntu partition (120 GB approx.)

Today, I created another partition F:\ from Windows 7 partition manager as follows.

System partition (105 MB approx.)
C:\
D:\
F:\
Ubuntu partition (120 GB approx.)

Also I accidentally assigned a drive letter to the Ubuntu partition as G:. Realizing my mistake I immediately removed the drive letter by hitting the remove menu from "Change Drive Letter and Paths".

After I restarted the PC, I'm getting the following error message screen:

error: unknown filesystem.
Entering rescue mode...
grub rescue> 

on ls at this screen I get following output: (hd0) (hd0,msdos4) (hd0,msdos3) (hd0,msdos2) (hd0,msdos1)

I tried the following commands ranging from

(hd0), (hd0,msdos6), (hd0,msdos5), (hd0,msdos4), (hd0,msdos3), (hd0,msdos2), (hd0,msdos1)

set boot=(hd0,msdos6)
set prefix=(hd0,msdos6)/boot/grub
insmod normal

But I'm getting either following error: error: unknown filesystem.

or: error: no such partition

I don't have windows live cd with me, but I've bootable USB with the same Ubuntu OS I've installed and can boot from that USB.

I want to be able to boot into Window 7 and Ubuntu both. Please let me know what do I need to do.

Any help / suggestion is appreciated.

UPDATE 1
Output of fdisk -l:

ubuntu@ubuntu:~$ sudo fdisk -l

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0xd8680f27

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1              63        2047         992+  42  SFS
Partition 1 does not start on physical sector boundary.
/dev/sda2   *        2048      206847      102400   42  SFS
/dev/sda3          206848   195350527    97571840   42  SFS
/dev/sda4       195350528   976771119   390710296   42  SFS

Disk /dev/sdb: 4023 MB, 4023385600 bytes
255 heads, 63 sectors/track, 489 cylinders, total 7858175 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: 0x9182a35b

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *          63     7858174     3929056    c  W95 FAT32 (LBA)
ubuntu@ubuntu:~$ 

Update 2

You can find the paste bin link below created by boot-repair:
http://paste.ubuntu.com/14678090/

Thanks & BR in advance,
Alkesh

  • Ubuntu is installed with ext4 file system which is not recognised by Windows, so my question is how can you assign its partition a letter? – Edward Torvalds Jan 26 '16 at 16:17
  • second question: did you tried grub repair? – Edward Torvalds Jan 26 '16 at 16:18
  • @edwardtorvalds because I had created the partition fro windows by shrinking the drive. So I could see it as unallocated space at the end. No I didnt try grub repair. Since the commands are not working in grub rescue. Besides I dont have any experience with Ubuntu system much. So If you can elaborate on that it would very be helpful. – iaL Jan 26 '16 at 16:20
  • try this answer askubuntu.com/a/182863/294611 – Edward Torvalds Jan 26 '16 at 16:25
  • @edwardtorvalds Ok thanks. Will try & update with results. – iaL Jan 26 '16 at 16:30
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The fact that GRUB is reporting partitions of the form (hd0,msdos##) means you've got an MBR partition table and are booting in BIOS mode. This means you've run into a big minefield: The Windows partitioning tools are terrible at handling extended and logical partitions on MBR disks. I've seen many posts from people whose disks have been seriously damaged by the Windows partitioning tools, usually because the Windows tools delete or otherwise damage logical partitions. In some cases, Windows converts a standard disk into one that uses the Microsoft-specific Logical Disk Manager (LDM) format. Because you've provided no partition table details, I can't be sure this is what's happened to you, but the odds are pretty good that it is. To be sure, please boot an Ubuntu live disk, run the following command, and post the results back here:

sudo fdisk -l

Be sure to post the results by editing your original question! Also, please add four spaces to the start of each line of the fdisk output; this flags it to preserve the formatting, which will become illegible if you don't do this.

Depending on how bad the damage is, you might be able to correct it with my FixParts program, which is part of the gdisk package in Ubuntu; or you might need to use the TestDisk program. You might even need to resort to more advanced tools or recover everything from a backup.

  • You cannot create more than 4 partitions with Windows without it converting to SFS or dynamic partitions. SFS is not compatible with Linux and does not even work with some Windows tools. Microsoft does not have an undo, just backup, erase drive & restore data. Some third party Windows tools may work But best to house clean down to 4 partitions and still need really good backups. ubuntuforums.org/showthread.php?t=1705481 – oldfred Feb 2 '16 at 18:45
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I tried repairing with boot rescue, but closed in the middle-way because I did not quite understand what it was trying to do. That I guess further worsened the grub and chances of booting into Ubuntu.

After further consulting our system admin, I came to know that the partition disks have been converted to dynamic disks by microsoft windows. And once converted to dynamic disk, you cannot change it back to primary partition. So ultimately had to recreate the partitions, format the PC & reinstall everything.

Thanks for all the help & support.

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