Re: legacy-bios and uefi boot usb stick

[Pascal Hambourg]

Le 14/05/2017 à 13:12, John Frankish a écrit :
> > > I've made a couple of dual legacy-bios/uefi boot usb sticks using grub-2.00.
> > >
> > > Both of the usb sticks will uefi boot linux, but there appears to be a problem 
> > > with legacy-bios boot of linux.
> > >
> > > One of the usb sticks gives an "invalid partition table!" error
> > What displays the message ? GRUB or the BIOS firmware ? Do you get the GRUB 
> > rescue prompt ?
> > Some BIOS firmwares require that a primary partition has the boot flag.
> It seems as though it is grub displaying the message.
>
> In one case I get the "invalid partition table!" message and have to cycle the 
> power

If the message was displayed by GRUB, I believe that you would at least 
get the GRUB rescue prompt.

> It is true that the usb stick that boots has the efi partition set as bootable 
> and the usb stick that fails to boot does not. Since both boot uefi I assumed 
> this did not matter.

The boot flag is meaningless for UEFI boot, since boot sectors are not used.

> Can fdisk be used to set the partition as bootable without data loss?

Yes.

> > This looks like a very old version of fdisk. Cylinders are obsolete. Add -u to 
> > use sectors as unit instead.
> It is a recent busybox version of fdisk.

Too bad is still uses obsolete metrics.

> By my calculation and by gparted, there is about 1.27mb before the first 
> partition.

Whatever. A GRUB BIOS core image takes less than 100 kB.