XPost: uk.comp.os.linux, alt.comp.microsoft.windows, alt.comp.os.windows-11   
   From: nospam@needed.invalid   
      
   On Mon, 11/10/2025 7:27 PM, Java Jive wrote:   
   > 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-gru   
   -to-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   
      
   [continued in next message]   
      
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