Cannot find root partition

Question

I have a problem with my laptop. I installed Ubuntu 14.04 LTS next to Windows 8.1. It is the first time I am using Ubuntu. I don't know exactly what happened but somehow I damaged the Grub bootloader. So I am trying to recover it now and I am following this tutorial:

English tutorial

They both say, I have to mount my root partition. So I am searching for it via

sudo gparted

which gives me the following:

... seems like I am not allowed to post the pictures here ...

so here is what sudo parted -l gives me:

ubuntu@ubuntu:~$ sudo parted -l
Model: ATA SanDisk SSD U100 (scsi)
Disk /dev/sda: 16.0GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  16.0GB  16.0GB               HFS


Warning: /dev/sdb contains GPT signatures, indicating that it has a GPT table.
However, it does not have a valid fake msdos partition table, as it should.
Perhaps it was corrupted -- possibly by a program that doesn't understand GPT
partition tables.  Or perhaps you deleted the GPT table, and are now using an
msdos partition table.  Is this a GPT partition table?
Yes/No? y                                                                 
Model: ATA ST1000LM024 HN-M (scsi)
Disk /dev/sdb: 1000GB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt

Number  Start   End     Size    File system     Name                          Flags
 1      1049kB  1050MB  1049MB  ntfs            Basic data partition          hidden, diag
 2      1050MB  1322MB  273MB   fat32           EFI system partition          boot, hidden
 3      1322MB  2371MB  1049MB  fat32           Basic data partition          hidden
 4      2371MB  2505MB  134MB                   Microsoft reserved partition  msftres
 5      2505MB  632GB   629GB   ntfs            Basic data partition          msftdata
 6      632GB   742GB   110GB   ntfs            Basic data partition          msftdata
 7      742GB   772GB   30.1GB  fat32                                         boot
12      772GB   943GB   171GB   ext4
13      943GB   951GB   8535MB  linux-swap(v1)
 8      951GB   952GB   472MB   ntfs                                          hidden, diag
 9      952GB   952GB   367MB   ntfs                                          hidden, diag
10      952GB   979GB   26.8GB  ntfs            Basic data partition          msftdata
11      979GB   1000GB  21.5GB  ntfs            Basic data partition          hidden, diag


Model: SanDisk Ultra (scsi)
Disk /dev/sdc: 16.0GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    Type     File system  Flags
 1      98.3kB  16.0GB  16.0GB  primary  fat32        boot, lba

According to the tutorial my root partition should be /dev/sdb12 because it is in ext4-format, right?`

But when I try to mount it via

sudo mount /dev/sdb12 /mnt

it says

mount: special device /dev/sdb12 does not exist

A list of recognized drives and partitions by my system (ls /dev/sd*):

/dev/sda  /dev/sda1
/dev/sdb  /dev/sdb1  /dev/sdb2  /dev/sdb3
/dev/sdc  /dev/sdc1

I really hope you can help me.

score 2 · Accepted Answer · answered Apr 10 '15 at 18:57

Here's your problem:

Warning: /dev/sdb contains GPT signatures, indicating that it has a GPT table.
However, it does not have a valid fake msdos partition table, as it should.
Perhaps it was corrupted -- possibly by a program that doesn't understand GPT
partition tables.  Or perhaps you deleted the GPT table, and are now using an
msdos partition table.  Is this a GPT partition table?
Yes/No? y

I started to write a response telling you how to fix it, but there are just too many decision points to do that without writing a small book. In the meantime, STOP USING THE DISK. Some possible configurations of that disk are DANGEROUS, and you might end up trashing important data if you write more data to the disk.

The simplest fix is to wipe the disk and start over. If you've got important user data, back up first. To do so safely, mount whatever you can read-only.

If you really need to recover it in place, it may be possible, but will require a number of checks and expertise to figure out the correct course of action. If you want to start this, please show the output of:

sudo fdisk -l /dev/sdb

...and also, the same parted output you showed, but use unit s print rather than simply print.

FYI, I expect that you used a GPT-unaware tool to partition the disk, which left you with an MBR disk with leftover GPT data. This configuration confuses parted. Somehow you managed to create new GPT partitions without damaging the MBR data. Windows' partitioning tools are known to create a fresh MBR without wiping GPT data, so installing Windows will sometimes do this.

Cannot find root partition

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