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I have a SATA hard drive with an MS DOS MBR partition table, an ext4 Linux-based OS, an NTFS Windows 7, and an extended partition. I was happily using my ext4 partition for quite some time, but grew anxious to return to my extensive Steam games collection. So, I then made the mistake of installing Microsoft Windows 7. Now, the system loads the MS bootloader instead of GRUB, and when I try to change the default OS, it only registers Windows as being an OS on the computer. I would hate to think that in all of their "expertise" the MS crew couldn't even write something to recognize that ext4 partitions exist. So, how can I change the main bootloader back to GRUB? I could always load both OS's with GRUB before, but now I don't know what is going on.

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Possible duplicate of Repair grub mbr and /boot using ubuntu 9.04 live CD, How to fix GRUB after Windows breaks it, and how to edit the GRUB menu etc. MS can accommodate Linux but chooses not to, since it probably doesn't want to facilitate the usage of other OSes. It is Linux that has always had to figure out how to play nice with Windows, NTFS etc., never the other way round. Anyway, you messed up the bootloader and it's an easy fix. This is why Linux should preferably be installed after Windows always. – Karan Jun 4 '13 at 21:04

Use the tool Boot-Repair.

Boot-Repair lets you fix these issues with a simple click, which (generally reinstalls GRUB and) restores access to the operating systems you had installed before the issue.

enter image description here

The easiest way to use Boot-Repair is to burn one of the following disks and boot on it.

  1. Boot-Repair-Disk is a CD starting Boot-Repair automatically.
  2. Boot-Repair is also included in Linux-Secure-Remix.

Remark : you can also install the ISO on a live-USB (eg via UnetBootin or LiliUSB or Universal USB Installer).

Video demonstrating the use:

SourceForge page:

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Easiest option, in my opinion, would be to boot a live Linux disc (Ubuntu may be the easiest) and run Boot-repair.

As a summary:

Install Boot-Repair in Ubuntu

  • boot your computer on a Ubuntu live-CD or live-USB.

  • choose "Try Ubuntu"

  • connect internet

  • open a new Terminal, then type:

sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update

  • Press Enter.

  • Then type:

sudo apt-get install -y boot-repair && (boot-repair &)

  • Press Enter
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