RE: Create legacy bios/uefi dual boot usb stick

[John Frankish]

>>> > ..there is no error message, uefi boot works fine, but legacy bios 
>>> > boot fails with an "invalid partition table" error
>>> >
>>> Where this error comes from? I do not see this string in GRUB sources 
>>> and it really does not care; it would stop in rescue mode then
>>>
>> I guess the error message comes from the machine's bios - the legacy boot 
>> doesn't get as far as starting grub.
>>
>>> Recently someone reported problem with booting rescue image on legacy 
>>> BIOS
>>>  - it would refuse to consider medium bootable unless medium has
>>> *msdos* partition table with active partition. This sounds like it could be 
>>> the reason.
>>>
>> I'm not sure I understand - I thought the "EF02 BIOS boot partition" 
>> achieved this aim?
>>
>
> BIOS boot is still GPT partition.
>
>> If not, what would the gpt partition table above look like including an 
>> *msdos* partition table with active partition?
>>
>
> You can start with creating standard MSDOS partition table.
> 
> EFI should be able to boot from it as well; and there is MSDOS partition type 
> reserved for ESP (0xef).
> Install grub in MBR. If booting still fails, try to mark second partition 
> bootable.
>
Thanks, this works:

$ sudo fdisk /dev/sdc
...
   Device Boot      Start         End      Blocks  Id System
/dev/sdc1   *           2         128     1020127+ ef EFI (FAT-12/16/32)
/dev/sdc2             129        3797    29471242+ 83 Linux
...
$ sudo x86_64-grub-install --target=x86_64-efi 
--boot-directory=/mnt/sdc1/EFI/BOOT --efi-directory=/mnt/sdc1 --removable
Installation finished. No error reported.

$ sudo x86_64-grub-install --target=i386-pc --boot-directory=/mnt/sdc1/EFI/BOOT 
/dev/sdc
Installation finished. No error reported.

..and both legacy-bios and uefi boot work.

I still don't see why this doesn't work on gpt formatted media, but fine..

...and now (eventually) for the legacy-bios/uefi boot cd/iso ;)