can't boot Grub2 with Win10 BCD boot manager

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  1. Posts : 13
    Windows 10 Pro
       #1

    can't boot Grub2 with Win10 BCD boot manager


    For years, I've been able to switch back and forth between Ubuntu's Grub boot manager and Windows 7's boot manager on my laptop's SSD before actually selecting one or the other OS to boot. When I selected Windows on the Grub menu, the Win7 boot manager would present its menu which included Ubuntu. If I then selected Ubuntu, Grub would bring up its boot menu which included Windows. But now, with Win10, selecting Ubuntu from the Windows boot menu doesn't launch Ubuntu's Grub2, but instead results in a BIOS POST. (My laptop doesn't have UEFI.) With Grub, I am still able to select either to launch Ubuntu 18.04 or to launch Windows 10's boot manager, so I can thereby run either OS. The aesthetic objection is the asymetry, and the problem is almost certainly with Windows 10's BCD operation.

    Running "bcdedit /v" in Win10's Powershell, the Ubuntu entry seen is:

    Real-mode Boot Sector
    ---------------------
    identifier {916e05e4-d073-11e8-a243-001e4ce02067}
    device partition=C:
    path \mbr.bin
    description Ubuntu 18.04

    where \mbr.bin is a copy of the SSD device MBR after Ubuntu was installed. It presumably is fine because as the 1st 512 bytes of the SSD, it gets control from the BIOS and causes Ubuntu's Grub2 boot manager to launch, from which I can select either Ubuntu or Windows. But for some reason, \mbr.bin doesn't seem to work. When I run "dir" on Powershell, it shows the attributes of \mbr.bin to be -a---- . Is that enough attribute to allow the system to run it? Or should I add some other file attribute(s) to allow it to run?

    TimDaniels
      My Computer


  2. Posts : 31
    Win10 Home 64-bit, MX-Linux
       #2

    Windows 10 also broke my "symmetric" Windows/Linux dual boot setup. I repaired it by using the EasyBCD program to install
    an "AutoNeoGrub.mbr" in the Windows filesystem. That file also has only the A attribute, so I don't think that's your problem.
      My Computer


  3. Posts : 13
    Windows 10 Pro
    Thread Starter
       #3

    Win10 seems harsher on dual-booting Linux


    kreemoweet said:
    Windows 10 also broke my "symmetric" Windows/Linux dual boot setup. I repaired it by using the EasyBCD
    Verrry eeenteresteeeng . . . Win10 seems to be harsher than previous Windows versions on dual-booting other OSes. EasyBCD seems to have figured it out, but I've been studiously avoiding that crutch since Win7, and I'm trying to set up the dual-boot to Ubuntu without resorting to EasyBCD. I expect that the solution is elegantly simple, but no one is telling what it is . . . , although someone intimately familiar with Win10 would know, and you'd think this would be a good place to start.
    . . . to install an "AutoNeoGrub.mbr" in the Windows filesystem. That file also has only the A attribute, so I don't think that's your problem.
    I agree. I checked out Windows' \windows\system32\winload.exe, the Windows boot loader, and it doesn't have any more in the way of attributes or permissions than what the copy of the Ubuntu-altered MBR has.

    Thanks for your reply. It at least tells me that I haven't done something uniquely stupid.

    TimDaniels
      My Computer


  4. Posts : 13
    Windows 10 Pro
    Thread Starter
       #4

    kreemoweet said:
    Windows 10 also broke my "symmetric" Windows/Linux dual boot setup. I repaired it by using the EasyBCD program . . .
    Kreemo! Would you please run bcdedit on Powershell with admin privileges and show us what is displayed below the line "Real-mode Boot Sector"? It might show an instruction line that EasyBCD has added since earlier versions of BCD/Windows.

    TimDaniels
      My Computer


  5. Posts : 31
    Win10 Home 64-bit, MX-Linux
       #5

    Here's what I have:
    Real-mode Boot Sector
    ---------------------
    identifier {5a9f4b25-2e2f-11e8-bdf5-001d6032e6cc}
    device partition=C:
    path \NST\AutoNeoGrub0.mbr
    description GRUB Menu
    locale en-US
    custom:250000c2 0

    That custom element 250000c2 business is explained here: Boot menu policy - set text or graphical style boot menu Windows 8
      My Computer


  6. Posts : 25,637
    Windows 11 Pro 22621.1
       #6

    When I Dual booted Win 10 with Linux I just used Grub2 to manage it.
      My Computer


  7. Posts : 13
    Windows 10 Pro
    Thread Starter
       #7

    kreemoweet said:
    Here's what I have:
    Real-mode Boot Sector
    ---------------------
    Thanks for the posting, KreemOWeet. I added the "locale" and "custom:250000c2" parameters, and I changed the MBR file name and the "path" so that "mbr" was the name extension, but POST still appears instead of Grub2. I'll continue experimenting with bcdedit parameters and with re-installing Ubuntu for a while, though.

    TimDaniels
      My Computer


  8. Posts : 13
    Windows 10 Pro
    Thread Starter
       #8

    Josey Wales said:
    When I Dual booted Win 10 with Linux I just used Grub2 to manage it.
    The whole point of this effort is to use BOTH Grub2 and Windows boot managers, each having the other as one of the options on its menu, allowing one to continually switch back and forth between boot managers before finally settling on an OS to launch. That's what KreemOWeet meant by "symmetry". Just one of several reasons is that Grub's boot menu is ugly, and by resetting the MBR to boot Windows, the pretty Windows graphical menu always appears after POST, which is especially fine if one usually wants to launch Windows (as I do). But currently, I have to suffer Grub's ugly text-only menu after every POST <shiver> if I am to continue dual-booting.

    TimDaniels
      My Computer


  9. Posts : 5,478
    2004
       #9

    TimDaniels said:
    Thanks for the posting, KreemOWeet. I added the "locale" and "custom:250000c2" parameters, and I changed the MBR file name and the "path" so that "mbr" was the name extension, but POST still appears instead of Grub2. I'll continue experimenting with bcdedit parameters and with re-installing Ubuntu for a while, though
    This is mine :
    Code:
    Real-mode Boot Sector
    ---------------------
    identifier              {c45cfd20-d133-11e8-bafc-0017f2c2c895}
    device                  partition=C:
    path                    \NST\nst_linux.mbr
    description             Arch
    locale                  en-US
    custom:250000c2         0
    Code:
    PS C:\Windows\system32> ls -l C:\NST\nst_linux.mbr
    
    
        Directory: C:\NST
    
    
    Mode                LastWriteTime         Length Name
    ----                -------------         ------ ----
    -a----       24/05/2018     14:57            512 nst_linux.mbr
    So it looks like the name doesn't matter - other details are same as @kreemoweet .

    This was created by EasyBCD for syslinux (not grub) installed on the partition VBR at /dev/sda4 not the MBR at /dev/sda if that makes a difference.

    If it is going to POST you could check with HxD or similar if your .mbr file has something in it (isn't all zeros)

    can't boot Grub2 with Win10 BCD boot manager-capture.png

    and it doesn't look exactly the same as your Windows loader in sector 0 on your disk.

    can't boot Grub2 with Win10 BCD boot manager-capture2.png
      My Computer


  10. Posts : 13
    Windows 10 Pro
    Thread Starter
       #10

    lx07 said:
    . . .
    If it is going to POST you could check with HxD or similar if your .mbr file has something in it (isn't all zeros)
    I used Notepad to show that the 512-byte file contained "gibberish", not all zeroes. I assume that since the MBR at sector 0 of the device (a Corsair Neutron 240GB SSD) leads to execution of Grub2 after POST, the copy of it as executed by the Windows boot manager should do the same thing, i.e. launch Grub2.
    and it doesn't look exactly the same as your Windows loader in sector 0 on your disk.
    What currently is in sector 0 leads to execution of Grub2, since Ubuntu was installed after Windows, and the sector 0 MBR was modified so that would happen. If I'm able to get the Windows boot manager to launch Grub2 (as I used to be able to do with Win7 Pro), I'll restore the sector 0 MBR with "bootrec /fixmbr" so the standard boot manager to get control after POST would be the Windows boot manager. But so far, no luck.

    TimDaniels
    Last edited by TimDaniels; 26 Nov 2018 at 02:05. Reason: typo
      My Computer


 

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