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Thread: Reinstalling Windows on dual boot system

  1. #1
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    Reinstalling Windows on dual boot system

    I have a laptop on which were windows on the hard drive and ubuntu on an internal SSD.

    Windows has been completely trashed and I am in the process of re-installing it.

    I am told that the ubuntu instance is intact and not disturbed.

    I have a live ubuntu of the same ilk.

    How do I start the ubuntu again when windows has trashed grub?

  2. #2
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    Re: Reinstalling Windows on dual boot system

    Why would Windows do that? "Trashed Grub", I mean.

    What is your problem exactly?

  3. #3
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    Re: Reinstalling Windows on dual boot system

    If installation of windows does mess up grub, just boot to your Ubuntu USB install boot repair and install grub. It is possible that windows will leave grub alone.

  4. #4
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    Re: Reinstalling Windows on dual boot system

    That shouldn't be a problem at all in any modern UEFI system, hence my question.
    Most of the times is users not understanding how UEFI boot process works, not understanding that bootloaders co-exist in the ESP (EFI System Partition) and that they can be booted independently.
    Unlike what happens with BIOS/MBR, removing one OS does NOT warrant re-installation of the other's bootloader in the vast majority of cases.

  5. #5
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    Re: Reinstalling Windows on dual boot system

    There are still plenty of legacy (i.e., uefi in legacy mode or simple bios) computers around. Basically every computer that originally came with preinstalled Windows 7 or before, which are most computers older than 8 years. Given that computers tend to last for 10–15 years, that could be around 30% of computers still in use.

  6. #6
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    Re: Reinstalling Windows on dual boot system

    Yes, but those UEFI machines that had the preinstalled Windows 7 in Legacy mode shouldn't count because that can and should be installed in UEFI mode. Why they were sold like this has to do with vendors' laziness in updating drive images. Windows 7 could have been installed in UEFI mode easily. One redeeming factor could have been the "downgrade to Windows XP" option some of those machines came with.

  7. #7
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    Re: Reinstalling Windows on dual boot system

    Windows is installed and on boot the machine boots into windows.

    I assume therefore that grub has been overwritten in the bootloader and grub needs to be reinstalled.

    My question becomes, on which drive do I install grub and how?

    The machine will normally boot the hard drive so I expect grub should be installed there?

  8. #8
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    Re: Reinstalling Windows on dual boot system

    I assume therefore that grub has been overwritten in the bootloader and grub needs to be reinstalled.
    Correct assumption for BIOS systems; totally incorrect for UEFI.
    Please check UEFI settings > Boot and where "Windows bootloader manager" is set it back to "Ubuntu". Then boot Ubuntu and run 'sudo update-grub' in terminal.

    https://help.ubuntu.com/community/UEFI
    This ^^^ page has been up for many years now.

  9. #9
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    Re: Reinstalling Windows on dual boot system

    If it is windows 8.1 or 10 then fast boot is on, disable it in windows. Boot to you ubuntu USB install boot repair and use pastebin to paste output, no repair yet. Let these people see what you are working with first. https://help.ubuntu.com/community/Re...tallingWindows

  10. #10
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    Re: Reinstalling Windows on dual boot system

    The machine will normally boot the hard drive so I expect grub should be installed there?
    Again, this is textbook example of the "not understanding UEFI" problem.
    In UEFI any OS is booted from the ESP (EFI System Partition) - the link above also explains this - no matter where any given OS is installed. Although "boot the hard drive" would have make more sense in BIOS times, even then it wasn't true either. This again reveals a misunderstanding of the boot process.

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