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Thread: Dual Booting Understanding of what's going on.

  1. #1
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    Default Dual Booting Understanding of what's going on.

    Hi,

    I have just added Tumbleweed to a drive with Windows 8.1 on it and created a good dual boot drive. All went well and the installer sorted it all out for me with no issues. I even have a VHD on the Windows partition and can boot that VHD too at the Windows boot loader as I have added it to the BCD; so all is working solidly.

    I want to understand a bit more about what happened with the boot loaders and where things were installed, and wondering if someone can either explain or point me the appropriate documentation.

    My configuration is as follows:
    I am working in a legacy environment and no EFI stuff.
    Partition 1 is for windows
    Partition 2 is Tumbleweed
    Partition 3 is linux swap
    There is no other partition like you get with windows 10 as a reserved partition at the beginning of the drive.

    So where are the various boot loaders stored etc, and how are they chained? What does the MBR point to? And any other questions I have failed to ask

    Thanks in advance.

    PS And, Yes, I have disabled Fast Startup on Windows before the whole disk gets corrupted

  2. #2
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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by JulinaB View Post
    What does the MBR point to?
    Active partition assuming you are using generic code. Otherwise you need to start with describing your boot configuration that we do not know.

  3. #3
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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by arvidjaar View Post
    Active partition assuming you are using generic code. Otherwise you need to start with describing your boot configuration that we do not know.
    I think this maybe a bit chicken and egg here. I just added Tumbleweed to an existing Windows booting disk and I am trying to work out what it has done so I get a better understanding of how it all works.

    Going into YaST Boot Loader Module, it indicates that the boot code location is set to MBR (/dev/sda), or at least that is what is selected. So presumably this means that GRUB was installed on the drive at the top level and not on an individual partition. What I am trying to work out is how Windows is booted and what GRUB does to transfer control to the windows bootloader which it does as I get the windows screen up offering me a choice of Win 8 or native boot into a VHD on the windows partition.

  4. #4
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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by JulinaB View Post
    Going into YaST Boot Loader Module, it indicates that the boot code location is set to MBR (/dev/sda), or at least that is what is selected. So presumably this means that GRUB was installed on the drive at the top level and not on an individual partition.
    Yes.
    What I am trying to work out is how Windows is booted
    I do not know. How do you boot Windows now?

  5. #5
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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by JulinaB View Post
    ...

    I want to understand a bit more about what happened with the boot loaders and where things were installed, and wondering if someone can either explain or point me the appropriate documentation.
    I personally started with

    https://en.wikipedia.org/wiki/Master_boot_record

    and worked through it; i.e. followed the links especially the ones given in the section "See also".

    Regards

    susejunky

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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by JulinaB View Post
    I am working in a legacy environment and no EFI stuff.
    Partition 1 is for windows
    Partition 2 is Tumbleweed
    Partition 3 is linux swap
    This is too generic a description. Reports from disk partitioning tools provide the detail required to describe what you have, e.g. fdisk -l or parted -l run by root or using sudo, complete with the exact command preceding output as you see on screen, and enclosed within code tags. To really learn a lot, you could run bootinfoscript. From its output you might learn all you want just examining it, no need for us.

    My guess is Grub2 was installed on the MBR to load a Grub menu from the TW filesystem, and a Windows selection has been included in Grub's menu for Grub to chainload the Windows bootloader.
    Reg. Linux User #211409 *** multibooting since 1992
    Primary: 15.2, +TW, 15.3, 15.1 & 13.1 on Haswell
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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by mrmazda View Post
    run by root or using sudo,
    Just a small off-topic.
    I saw you say so somewhere else also. And while it will not lead to anything going wrong, it may lead to misunderstanding when people read this.

    sudo is just one way of starting a root owned process. Thus it is not "run by root or using sudo,", but "run by root e.g. by using sudo,"
    Henk van Velden

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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by mrmazda View Post
    This is too generic a description. Reports from disk partitioning tools provide the detail required to describe what you have, e.g. fdisk -l or parted -l run by root or using sudo, complete with the exact command preceding output as you see on screen, and enclosed within code tags. To really learn a lot, you could run bootinfoscript. From its output you might learn all you want just examining it, no need for us.

    My guess is Grub2 was installed on the MBR to load a Grub menu from the TW filesystem, and a Windows selection has been included in Grub's menu for Grub to chainload the Windows bootloader.
    bootinfoscript was a great help and I think I have worked out what is going on. Yes, GRUB2 is installed in the MBR and I can see how the bootloaders are chained (GRUB -> Windows). What I really want is to have them chain the other way round and have Tumbleweed available as a boot option in the Windows boot menu which should launch first. Looks possible provided I can make a FAT32 /boot partition, as Windows can't see ext4.

    https://wiki.archlinux.org/title/Dua...s_before_Linux

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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by hcvv View Post
    it is not "run by root or using sudo,", but "run by root e.g. by using sudo,"
    The implication as I wrote it was run (directly) by (logged in) root or (root indirectly) by using (the) sudo (shortcut).
    Reg. Linux User #211409 *** multibooting since 1992
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    Default Re: Dual Booting Understanding of what's going on.

    Quote Originally Posted by JulinaB View Post
    What I really want is to have them chain the other way round and have Tumbleweed available as a boot option in the Windows boot menu which should launch first. Looks possible provided I can make a FAT32 /boot partition, as Windows can't see ext4.
    There's no FAT32 requirement. Grub must be installed to a partition. Generic MBR code must be installed. A boot flag must be set on only the Windows primary responsible for booting. Subsequently, Windows' bootloader can be configured to chainload to Grub. I used to do it long ago, before Vista, on multiboot installations for other people not yet comfortable with Linux. I would make the Windows primary small (400MB or less), and its system partition on the slow end of the HDD, after everything Linux.

    What's nice about the way you want Windows first is the Windows update process won't waste your time doing/undoing/redoing/undoing/... updates because it doesn't find a boot flag where it expects one to be. Using Windows' own MBR code, there must be one and only one boot flag per bootable disk's MBR table. Boot flags on logical partitions IME doesn't get it flustered, but since I never have any, I can't be sure.
    Reg. Linux User #211409 *** multibooting since 1992
    Primary: 15.2, +TW, 15.3, 15.1 & 13.1 on Haswell
    Secondary: eComStation (OS/2) &15.2 on i965P w/ Radeon
    Tertiary: Mageia,Fedora,Debian,more on Kaby Lake,iQ45,iQ43,iG41,iG3X,i965G,AMD,NVidia&&&&&

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