XPost: uk.comp.os.linux, alt.comp.microsoft.windows, alt.comp.os.windows-11   
   From: java@evij.com.invalid   
      
   On 2025-10-31 12:56, Java Jive wrote:   
   >   
   > As per subject, as I now have on the same PC some OSs  -  Ubuntu24,   
   > Windows7/10  -  installed on an MBR disk and Windows 11 installed on a   
   > GPT/UEFI disk, I'd like if possible to find a way of booting any of   
   > them, and MBR/GPT USB sticks, without constantly having to change the   
   > BIOS settings on the PC.   
   >   
   > Research into whether this is possible seems to produce mixed results,   
   > mostly not, but a few suggesting it's possible, but I haven't yet found   
   > anything with clear and understandable instructions on how to achieve it.   
   >   
   > My own gut feeling is that it should be possible, but, while I have a   
   > good understanding of how a PC boots an MBR disk, I have less   
   > understanding how one boots a GPT/UEFI disk.   
   >   
   > Has anyone here been able to achieve this?  Does anyone know of good   
   > reliable sources of information about this?   
      
   Thanks for the earlier responses, I have now some success to report ...   
      
   You may recall the disk layout I was trying to achieve success with:   
      
   Disk 1:  256GB (nominal) SSD - MBR partitioning   
        P1:  Win  7 Pro, NTFS   
        P2:  Win 10 Pro, NTFS   
        P3:  Win  7 32-Bit Pro, NTFS   
                (for old scanner with only 32-bit drivers)   
        P4:  Ubuntu 24, ext4   
      
   Disk 2:  2TB (nominal) HD - MBR partitioning   
        P1:  Windows Data, NTFS   
        P2:  Linux Data, ext4   
      
   Disk 3:  128GB (nominal) MiniSSD - GPT partitioning   
        P1:  128MB UEFI Boot, FAT32   
        P2:  Win 11 Pro, NTFS   
      
   Before I started this work, when booted via MBR and Disk 1, Grub gave   
   access to all the OSs except W11P, while when booted via UEFI/GPT and   
   Disk 3, only W11P could be booted, whereas obviously I wanted to have   
   just one method of booting every OS.   
      
   Therefore the question was, should I try to find a way of booting W11P   
   via UEFI from the legacy Grub installation on D1, which would have   
   required some sort of forward compatibility of the legacy MBR   
   installation, or should I attempt to load all the other OSs via UEFI via   
   a new Grub installation on D3, which would require backward   
   compatibility?  I felt the chances of forward compatibility were less   
   than the chances of backward compatibility, so, despite the extra work   
   involved, and certainly it was a great deal of work, I chose the latter.   
      
   However, as it has turned out, I've only been able to achieve partial   
   backward compatibility in that all the 64-bit OSs can now be booted from   
   D3, but not the 32-bit OS, I've not been able to find a way of booting   
   Win 7 Pro 32-Bit from UEFI.  Further, I have not been able to find a way   
   of booting *ANY* 32-Bit OS, not even a UEFI boot Win 8 Pro 32-Bit   
   installation USB, when using UEFI on that particular PC (so probably   
   none of the others either, because they're all identical or nearly so),   
   so I suspect that this is a firmware limitation with this range of PCs.   
      
   FTR, this is how I got the other 64-Bit OSs to boot from Grub on the GPT   
   disk, even though they themselves are on an MBR disk ...   
      
   1)  I renamed MS' D3P1:/Boot folder to 'boot', ie all lower case.   
      
   2)  I copied the previous MBR grub installation from D1P4:/boot/grub to   
   D3P1:/boot/grub.   
      
   3)  Similarly, I copied the UEFI grub installation from an Ubuntu 24   
   installation USB over the previously copied files in D3P1:/boot/grub.   
      
   4)  In the PC's firmware, I set up a new boot option named 'Grub' to   
   boot ...   
   	D3P1:/EFI/Boot/grubx64.efi   
      
   As as result I was now able to boot into Grub displaying the previous   
   menu from the MBR disk (because in step 2 I'd copied the grub.cfg across   
   with everything else and taken steps to prevent it being lost in step   
   3), but of course most of the options didn't work.   
      
   However, the existing Ubuntu 24 installation was able to boot from this   
   new Grub menu, the only discernible difference being that an additional   
   initial message is displayed briefly, it reads ...   
      
   EFI stub: Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path   
      
   ... and thereafter the boot proceeds apparently as normal.   
      
   5) Next, I thought it should be possible somehow to boot via UEFI into   
   Ubuntu and simply run 'update-grub' to complete the setup, as per this   
   advice ...   
      
   https://askubuntu.com/questions/831216/how-can-i-reinstall-grub-   
   o-the-efi-partition   
      
   ... but this proved a complete waste of time.  First I tried doing it   
   from the existing Ubuntu 24 installation; when booted via UEFI, the EFI   
   system is available, but when doing a chroot to perform update-grub, the   
   EFI subsystem and its associated variables were lost.  So next I tried   
   booting via EFI from an Ubuntu 24 installation USB, but the same thing   
   happened.  Finally, after much machination I installed a separate UEFI   
   Ubuntu 24 on a spare disk and booted from that, and finally succeeded in   
   getting the EFI subsystem available within the chroot, but update-grub   
   didn't find the other OSs on the MBR disk anyway, although it did now   
   complete without error and so create a working entry for the W11P   
   installation on the GPT disk, which reads (beware unintended line-wrap):   
      
   5a) menuentry 'Windows Boot Manager (on /dev/sdc1)' --class windows   
   --class os $menuentry_id_option 'osprober-efi-1043-DB71' {   
   	savedefault   
   	insmod part_gpt   
   	insmod fat   
   	set root='hd2,gpt1'   
   	if [ x$feature_platform_search_hint = xy ]; then   
   	  search --no-floppy --fs-uuid --set=root --hint-bios=hd2,gpt1   
   --hint-efi=hd2,gpt1 --hint-baremetal=ahci2,gpt1 1043-DB71   
   	else   
   	  search --no-floppy --fs-uuid --set=root 1043-DB71   
   	fi   
   	chainloader /EFI/Microsoft/Boot/bootmgfw.efi   
   }   
      
   But for the others I had to wing it, using little clues from various   
   researches online, none of which gave a complete template or revealed a   
   crucial extra step to get Windows 7 & 10 to boot, which is that you need   
   to load the module 'ntfscomp'  -  I guess comp is short for 'compatible'   
   or some related word.  Also, you can't use drivemap but anyway don't   
   need to, and you have to change the 'chainloader' command, like so ...   
      
   6)  Change a current MBR menu item of this form ...   
      
   menuentry "Windows ... {   
        ...   
        insmod ntfs   
        ...   
        drivemap ...   
        chainloader +1   
   }   
      
   ... to a GPT equivalent of this form ...   
      
   menuentry "Windows ... {   
        ...   
        insmod ntfs   
        insmod ntfscomp   
        ...   
        chainloader /Windows/Boot/EFI/bootmgfw.efi   
   }   
      
   7)  The next thing to be done is to create the BCD files within the   
   relevant Windows installation(s).  This can be done by booting into a PE   
   environment, most probably from an installation media and then choosing   
   Repair ... Command Console.   
      
      
   [continued in next message]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)