RE: Cannot boot from dual bios/uefi boot CD

[John Frankish]

> > > > > > > >> >> >> > On Wed, Jan 28, 2015 at 10:30 AM, John Frankish 
> > > > > > > >> >> >> > <address@hidden> wrote:
> > > > > > >> > >> >> > Hi,
> > > > > >> > > >> >> >
> > > > > >> > >> > >> > I'm trying the create a dual bios/uefi boot iso 
> > > > > >> > >> > >> > to burn
> > > > >>>  >> > > >> > to CD/DVD and boot both bios and uefi.
> > > > >> >> > > >> > >
> > > > > >> >> > > >> And your grub version is?
> > > > > >> >> > >> >
> > > > > > >> >> > > 2.00
> > > > > > > >> >> >
> > > > > >> > >> Current is 2.02~beta2.
> > > > > > > grub-mkrescue creates ISO that is bootable by all platforms 
> > > > > > > for which grub support is installed. If your system has grub 
> > > > > > > for i386-pc and > x86_64-efi (and may be i386-efi) installed 
> > > > > > > under standard directory, grub-mkrescue will build ISO that 
> > > > > > > includes support for all three and is bootable on all three 
> > > > > > > platforms. If not, this is a bug. Which is one more reason 
> > > > > > > to use it :)
> > > > > > >
> > 
> > Grub-mkrescue does indeed make a legacy bios/efi boot cd that works (I 
> > note that it invokes grub-mkimage) :)
>
> You can now start with this invocation and extend it; at least you have 
> something that is known to work.
>
> > 
> > The trouble is that it copies all of the pc and efi modules to the iso 
> > making it larger than necessary.
>
> All modules take ~2M, so for two platforms it will be ca. 4MB if you skip all 
> fonts, locales and themes. What are you going > to do with this image if 4MB 
> is too much?
> >
My feeling is that linux should always strive to make things as small as 
possible - in some places it takes a long time to download 4MB
> > 
> > I presume I can use "--modules=" to embed only the modules required to boot 
> > a CD. To avoid burning another 20 coasters:
> > 
> > 1. What are the minimum modules required to boot only from CD/DVD and load 
> > a linux OS?
> > 
>
> I do not know. Seriously :)  I would tentatively presume iso9660, biosdisk 
> (for PC BIOS), part_msdos, part_gpt, normal, linux > and whatever 
> dependencies it pulls in. Basically it is whatever grub-mkrescue puts into 
> core.img + normal + loader for your > OS.
>
> > 2. Can I then delete all the modules from the iso and rebuild it with 
> > mkisofs/xorriso or is there a way to prevent grub-> mkrescue copying the 
> > modules?
> > 
>
> Did you try grub-mkrescue --help?
>
> grub-mkrescue --install-modules
>
I ran the following:

$ sudo x86_64-grub-mkrescue --modules="iso9660 fshelp loadbios part_msdos 
part_gpt normal terminal crypto extcmd boot gettext linux video relocator mmap 
font bufio efi_gop video_fb efi_uga gfxterm bitmap_scale bitmap gfxmenu trig" 
-o myiso.iso iso

The iso as-is boots, but still contains copies all of the modules in i386pc and 
x86_64-efi.

I don't see the logic in embedding modules if the same modules will be copied 
to the iso anyway?

If I delete the x86_64-efi folder from the iso, it doesn't boot and complains 
about all of the missing modules for ever.

Wouldn't it make more sense to either embed the modules or copy them to the 
iso, but not both?

In any case if the correct modules are embedded then the boot should not fail 
for the lack of the same modules under x86_64-efi.