Ubuntu – How to fix a corrupted partition table

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I was running a duel boot windows 8.1 and ubuntu 14.04 when I suddenly could no longer boot my system. After booting into a live usb and run GParted I get this error:

Input/output error during read on /dev/sdb

/dev/sda 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?

Both the primary and backup GPT tables are corrupt. Try making a fresh table, and using Parted's rescue feature to recover partitions.

Is there a way to fix this? I have tried TestDisk which won't run. Is there also a way I can backup my hard drive before I do anything that might damage my computer.

Best Answer

The simplest option is to try to use the backup GPT table. This is stored automatically on the disk. The gdisk utility can do all of this for you. Simply load as normal,

# gdisk /dev/sdb

And enter the recovery and transformation menu (r), and option c to load the backup table. If it's successful you can write the correct table back out again. It won't write anything until you tell it to.

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Ubuntu – Problems Installing Ubuntu 13.10 Alongside Windows 7 – gpart shows unallocated space

It is entirely possible that your disk has stray GUID partition table data (in this case, Windows will actually still boot happily, recognizing the disk as only MBR). Is your Windows installed in legacy BIOS mode?

To confirm this, from the Ubuntu Live Desktop environment, open a Terminal and install gdisk (ensure you have network connectivity):

sudo apt-get install gdisk

Then list partitions that are on the GUID partition table:

sudo gdisk -l /dev/sda

Chances are, it might have come up empty. In that case, you will need to preserve the MBR and drop the stray GUID partition table identifier entirely:

sudo fixparts /dev/sda
w

More information here: http://www.rodsbooks.com/fixparts/

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Chances are your disk originally contained a GUID Partition Table (GPT), but you created a new Master Boot Record (MBR) partition table over that with a tool that doesn't understand GPT. Because GPT takes up more space than MBR, this means that there's leftover GPT data, and parted is becoming confused because of that.

If this analysis is correct, then the easiest solution is to run FixParts on the disk. FixParts will offer to remove the leftover GPT data, and thereafter you should be able to use the disk normally. (You don't need to do anything else in FixParts; just tell it to remove the GPT data when it asks you about this and then exit.)

There is a caveat, though: It's also possible that you had a GPT disk but that something accidentally wrote an MBR partition table to the disk. In this case, you probably want to recover the GPT, not wipe it out! If this is the case, the solution is to run gdisk on the disk. It will detect the problem and ask if you want to use the GPT or MBR data. Tell it to use the GPT data, check that it's correct by typing p and comparing the output to whatever you believe to be correct, and then type w to save the changes.

Both FixParts (fixparts) and gdisk are part of the gdisk package in Ubuntu. It's usually not installed by default, so you may have to install it by typing sudo apt-get install gdisk.

Best Answer

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