RE: Create legacy bios/uefi dual boot usb stick

[John Frankish]

> > I've been trying, without success, to create a legacy bios/uefi dual 
> > boot usb stick.
> >
> > If I partition the usb stick using gdisk, like this:
> >
> >
> > $ sudo gdisk /dev/sdc
> > ...
> > Number  Start (sector)    End (sector)  Size       Code  Name
> >    1            2048         2097152   1023.0 MiB  EF00  EFI System
> >    2         2099200         2103295   2.0 MiB     EF02  BIOS boot partition
> >    3         2103296        61013982   28.1 GiB    8300  Linux filesystem
> >
> > If I then try:
> >
> > $ sudo x86_64-grub-install --target=i386-pc 
> > --boot-directory=/mnt/sdc3/boot /dev/sdc
> >
> >
> That's correct; but why do you use different boot directory?
> The whole point of using multiboot medium is to have *single* /boot grub
> (and whatever configuration, themes etc are there) that is used by every 
> platform.
> 
Good point - I'll do that :)

> > ..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?

If not, what would the gpt partition table above look like including an *msdos* 
partition table with active partition?