XPost: uk.comp.os.linux, alt.comp.microsoft.windows, alt.comp.os.windows-11   
   From: nospam@needed.invalid   
      
   On Fri, 10/31/2025 8:56 AM, 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?   
   >   
      
   It depends on whether this is a BIOS-mediated plan or a Pop-Up Boot   
   mediated plan.   
      
   The BIOS has a list of hard drives. If a drive   
   was not plugged in, maybe the BIOS moves on to   
   a new disk menu entry and considers it. But this does not   
   give much in the way of control, except if the user   
   is very confident that they know which disk   
   would be selected by the automation.   
      
   Whereas the Popup boot key, offers everything, on a UEFI/CSM BIOS.   
   The menu contents are determined by the ~25 second scan (for an HGST boot   
   drive which is slow).   
      
   I press F11 on this MSI motherboard computer, to access PopUp Boot. When the   
   scan is finished.   
   I press F8  on the Asus motherboqrd computer, to access PopUp Boot. When the   
   scan is finished.   
      
       CSM  First disk   
      
       UEFI Second disk    # This could be a hybrid entry, or a hybrid DVD   
       CSM  Second disk   
      
       UEFI Third disk   
      
       Windows Boot Manager # That's a UEFI, and it lists some sort of disk   
   identifier   
                            # The BIOS does not like multiple Windows Boot   
   Managers, and   
                            # it especially does not like them, if on TWO   
   IDENTICAL DISKS :-)   
                            # You can cursor one drive, and it selects the other   
   drive.   
      
       UEFI USB stick   
      
   I don't know if Secure Boot can be enabled, without forcing the menu   
   to only consider UEFI disks. UEFI/CSM mode might be with no Secure Boot.   
   Once Secure Boot is enabled, only the UEFI disks should be listed (two entries   
   in example).   
      
   In the PopUp Boot, you can cursor down to the item desired, and hit    
      
   This situation is most likely to occur, when the disks don't   
   know anything about one another, and you have slid the drive in   
   as desired to achieve a result. The BIOS scans the drive set it finds at   
   startup and puts entries for everything it finds. An entry that   
   hides a multiboot GRUB or Windows menu, would only occupy   
   one slot at this level, and once in a Windows tile menu, you could   
   select from a set of Windows OS partitions. Some of the partitions,   
   could even be on the other disk drives. If a disk drive is missing   
   and a Windows multiboot has entries, it is not fussed about a disk   
   drive gone missing... unless you hit  there and there is   
   no disk fitting that description present. The boot sub-menu in that   
   case is not validated on the fly.   
      
   I could see a boot sequence, using as many as three levels of menu.   
   For those of us who must be different.  BIOS --> GRUB --> WindowsTiles   
   I think I accidentally did that at least once (not intentional).   
      
   *******   
      
   If you have a "control disk" that directs all booting on subtending   
   disks, then GRUB would be best for that, as it handles both its   
   own kind of OS, plus using OS-Prober it can include Windows OSes.   
   That's why the last paragraph has that example. I know I can get   
   an additional menu level, but putting the GRUB in the middle   
   of the sandwich.   
      
   *******   
      
   Ubuntu24, Windows7/10  -  installed on an MBR disk   
   Windows 11                GPT/UEFI disk   
      
   USB Stick                 ???   
      
   OK, how I'd do that, is I make the first disk the "control disk".   
   As you likely installed Ubuntu24043 as a GRUB item and it was   
   installed second and GRUB now shows this when we perpetually   
   select the first disk so it steers the boot of other disks.   
      
        Ubuntu2404   
        Windows7   
        Windows10   
      
   If I do a    sudo update-grub   and OS-Prober is present while   
   Ubuntu2404 is running, and the Windows 11 disk drive is present,   
   then the GRUB may add the Windows to the menu during the update-grub run.   
   Now my control disk (the first disk) controls two disk drives.   
      
        Ubuntu2404   
        Windows7   
        Windows10   
        Windows11   
      
   In the BIOS, I set the BIOS to boot from the first (MBR) disk.   
   The GRUB comes up, I cursor down and select one of the four targets.   
      
   To launch the USB stick, I use the PopUp Boot key, and I select   
      
        UEFI USB           # some of mine are showing up without the namestring   
           USB             # for the USB hardware. The second one is CSM.   
      
             # I would select this to get to the four entry GRUB   
   menu   
      
   Some BIOS designs are just plain nasty, and follow no rules at all.   
   I've even had one report of a BIOS "that went nuts". I could not   
   make any sense whatsoever, out of the symptom description. The description   
   makes as much sense as my mall elevator (I pressed "5" yesterday, the door   
   closed, the elevator didn't move -- I pressed the "5" again, even though the   
   "5" was already lit, and... off we went).   
      
   While you can wave hands about these things, YMMV.   
      
   Just a guess,   
      Paul   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)