Re: Valid grub.conf locations

[Ulrich Sibiller]

Hello,

what exactly does "built to include networking support" mean here?
This non-working bootx64.efi includes many network modules, which can
be included using grub-mkimage (see also
https://github.com/PartialVolume/shredos.x86_64/issues/147#issuecomment-1593733621):
...
grub-mkimage: info: writing 704 bytes of a fixup block starting at 0x10000.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/terminal.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/gettext.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/bufio.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/boot.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/datetime.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/priority_queue.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/net.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/crypto.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/extcmd.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/normal.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/mmap.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/video.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/relocator.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/linux.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/video_fb.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/video_bochs.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/video_cirrus.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/efi_gop.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/efi_uga.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/all_video.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/archelp.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/newc.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/efinet.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/tftp.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/gcry_crc.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/gzio.mod.
grub-mkimage: info: reading /usr/lib/grub/x86_64-efi/part_gpt.mod.
grub-mkimage: info: kernel_img=0x7fd6d998b010, kernel_size=0x1c000.
grub-mkimage: info: the core size is 0xa03d0.
grub-mkimage: info: writing 0xa3000 bytes.

But even with them included the grub.conf is only loaded from the
provided prefix (-p option of grub-mkimage) /EFI/BOOT. So what's
missing?

If you run "make menuconfig in buildroot there's not much to select for grub2:
                                                    [*] grub2
                                                            Platform
(i386-pc)  --->
                                                      (hd0,msdos1)
boot partition
                                                     (boot linux ext2
fat squash4 part_msdos part_gpt normal biosdisk progress) builtin
modules
                                                     ()    builtin config
                                                      [*]   install tools



Uli

On Mon, Jun 19, 2023 at 4:06 PM Andrei Borzenkov <arvidjaar@gmail.com> wrote:
>
> On 19.06.2023 12:46, Ulrich Sibiller wrote:
> > Hello,
> >
> > I am wondering where grub is supposed to look for grub.cfg when booted
> > via PXE as grubx64.efi (or bootx64.efi)?
> >
> > Background: I have been playing around with running shredos
> > (https://github.com/PartialVolume/shredos.x86_64) over the network via
> > PXE. I failed with the bootx64.efi (which is grub2) coming with
> > shredos because it does not find grub.conf when booted via PXE/tftp.
> > It just checks /EFI/BOOT/grub.conf in this case. The grub in shredos
> > is built via GNU's buildroot using the official grub sources.
> >
> > So I tried with grubx64.efi as delivered by Centos7 and succeeded.
> > This grubx64.efi loads grub.conf - amongst other locations - from the
> > same path where the .efi file has been found:
> >
> > Jun 15 14:10:33 server in.tftpd[31076]: RRQ from 192.168.11.15
> > filename cluster/shredos/bootx64.efi
> > Jun 15 14:10:33 server in.tftpd[31076]: Client 192.168.11.15 finished
> > cluster/shredos/bootx64.efi
> > ...
> > Jun 15 14:10:40 server in.tftpd[31097]: RRQ from 192.168.11.15
> > filename cluster/shredos/grub.cfg
> > Jun 15 14:10:40 server in.tftpd[31097]: Client 192.168.11.15 finished
> > cluster/shredos/grub.cfg
> >
> > I think that the centos7 build works because it is patched to check
> > the fw_path variable. The official sources seem to not contain fw_path
> > at all.
> >
> > (if you want to know more details all this is described in some length
> > at https://github.com/PartialVolume/shredos.x86_64/issues/147)
> >
> > So is there a way to make the official grub look for grub.conf at the
> > same dir as the efi file when booting via PXE?
> >
>
> That is exactly what the official grub does when booted via PXE - as
> long as it was built to include networking support in the first place.
> And if $prefix is not hardcoded in core.efi. Without knowing how your
> grub binary is built it is hard to guess what could be wrong.
>