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RE: legacy-bios and uefi boot usb stick

From: John Frankish
Subject: RE: legacy-bios and uefi boot usb stick
Date: Sun, 14 May 2017 11:12:52 +0000

> > 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, in the other case it quickly shows an error message and then passes to 
the normal grub menu.

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.

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

> > $ fdisk -l /dev/sdb
> > 
> > Disk /dev/sdb: 62.2 GB, 62209916928 bytes
> > 118 heads, 22 sectors/track, 46804 cylinders Units = cylinders of 2596 
> > * 512 = 1329152 bytes
> >
> >    Device Boot      Start         End      Blocks  Id System
> > /dev/sdb1               2       46000    59706702  83 Linux
> > /dev/sdb2           46001       46804     1043592  ef EFI (FAT-12/16/32)
> > 
> 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.

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

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