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/dev/sda contains GPT signatures indicating that it has a GPT table. However, it has a fake msdos partition table as it should. Perhaps it was corrupted? Is this a GPT partition table?

So, that's the error message and this is during my first OS install of Ubuntu. Can close the message box. Can't click yes and can't click no. What do I do?

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Could you provide the error message that you received? – Kevin Bowen Jan 31 '13 at 4:19
    
just says i may have deleted the table or a program may have corrupted it for me – user127455 Jan 31 '13 at 4:39
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The error message you reported makes no sense, because the two conditions (GPT signature present and "fake" MS-DOS table) are in fact consistent with a valid GPT disk. I therefore suspect you've omitted a "not" or "doesn't" somewhere. Please check again. – Rod Smith Jan 31 '13 at 23:31
up vote 0 down vote accepted

I've seen a similar problem on my disk when I had a leftover partition from my windows 7 system. Went back to windows 7, and took all the partitions off using disk manager.

Also, make sure the disk is not "dynamic" in disk manager.

After that, I was able to do a clean install of ubuntu 12.1o :)

In case you don't have a system running windows 7, you can boot with a windows 7 dvd and run setup. Choose "advanced" when you get to choosing partition for the installation, and erase all partitions there.

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I am answering because the answers here are inadequate. I don't want future viewers of this question to destroy their windows partitions just to install Ubuntu.

To fix your problem, follow these steps:

  1. Boot the emergency disk (Ubuntu or other linux Live CD) and open a text-mode shell.
  2. Type gdisk /dev/sda (change /dev/sda to whatever is appropriate to access your hard disk, if necessary). The program is likely to complain that it's found both MBR and GPT data, and will ask which to use. It doesn't matter which you tell it to use.
  3. At the Command prompt, type x to enter the experts' menu.
  4. At the Expert command prompt, type z to zap (destroy) the GPT data.
  5. Type y in response to the confirmation about destroying the GPT.
  6. Type n in response to the query about blanking the MBR. Caution: If you answer y here, you'll destroy your Windows partition(s)!
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Jesus Christ, thank you! – Joe Jun 22 '14 at 4:13
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Same as above! jaja You saved me man! Thanks! – Pablo Aug 8 '14 at 23:16
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Obviously, this should be the accepted answer. – w0lf Mar 6 '15 at 14:39
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"The program 'gdisk' is currently not installed" Please let me know what to do? – shan Apr 5 '15 at 6:01
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Everyone who has Windows 8 in UEFI mode with gpt partitions and then reinstalls Windows in BIOS boot mode has this issue. Windows does not correctly convert from gpt to MBR(msdos). It leave backup gpt table. Better to use fixparts as a bit easier, but gdisk is good. Or better still just install Windows in UEFI mode, you may have to modify installer slighter if older version of Windows to have it work in UEFI mode. rodsbooks.com/fixparts – oldfred Apr 9 '15 at 19:42

NO NEED FOR A EMERGENCY DISK!!

Simply boot with ubuntu live CD or USB (I did with USB).

Then open the Terminal. Type: sudo gdisk (hit enter) Type: /dev/sda (change /dev/sda to whatever is appropriate to access your hard disk, if necessary). Then you will probably see that there are MBR and GPT. Tell the computer you want to use the MBR Then: At the Command prompt, type x to enter the experts' menu. At the Expert command prompt, type z to "zap" (destroy) the GPT data. Type y in response to the confirmation about destroying the GPT. Type n in response to the query about blanking the MBR. Caution: If you answer y here, you'll destroy your Windows partition(s)!

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I do not know why, however if this is a fresh install without ANY data being retained on the HDD boot up as the livecd then use gparted to clear the GPT table and make an msdos partition table.

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1  
can i do this on windows 7? – user127455 Jan 31 '13 at 4:14

I would like to answer about one of the causes that could lead to this complex situation.

I had a GPT system with Ubuntu 14.04, no Windows. I was unable to install Windows without wiping my disk. So, I took the necessary BACKUP (always do that no matter what simple thing you are doing) and wiped the disk using bootable Windows USB.

Now, the catch is, even if this automatically converts from GPT to MBR, somehow, it keeps signatures of GPT. So, any tool for managing the hard disk (like Gparted) gets confused as it founds GPT and MBR both. So, this will show all the disk space as unallocated as if you do NOT have Windows. But, if you check in your media, it will show the mountable drives, even, it will show all the data that your drive has.

Solution to this is - make a bootable USB with any Linux version. Live boot it and once the Linux starts, open the terminal and use gdisk utility to remove all corrupted GPT entries or Signatures.

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To add to the answer given by PitaJ (and improved by Roxy)

It's possible that using Live disk, you will be asked to open terminal as a root and it will give you an error on gdisk command. To do that you will need to do the following:

1) Open terminal

2) type sudo passwd root, it'll ask you to enter new password, enter any password

3)Type SU and enter password that you just used above.

Now you are in terminal as root, everything listed by PitaJ will work from here on.

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