Mailinglist Archive: opensuse (1352 mails)

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Re: [opensuse] a little help with Leap 15.0
On 2018-06-02 23:38, Knurpht @ openSUSE wrote:
Op zaterdag 2 juni 2018 22:14:55 CEST schreef Carlos E. R.:
On 2018-06-02 21:39, Knurpht @ openSUSE wrote:
Op zaterdag 2 juni 2018 21:14:59 CEST schreef Carlos E. R.:
On 2018-06-02 01:11, don fisher wrote:
I have been having a lot of trouble with upgrade, so pardon this if
stupid question.


The partition is used by grub boot code. In words from Andrei Borzenkov:

Thanks for elaborating. Note to self: Include "arvidjaar" in searches re.


"It used to store GRUB2 MBR-gap code (as MBR gap does not exist on GPR)".

"bios_boot partition contains grub2 core.img which (for btrfs on BIOS)
is about 40K. Still fits into 2M space but no more into legacy 63
post-MBR sectors."

"core.img is exactly *the* code that locates /boot/grub2 which
contains bulk of grub2. It is effectively copy of what is written into
bios_boot or other location where you chose to install grub2."

(just a quick search, I know he has explained what it is needed for more
than once ;-) )

Thus it is not ever needed mounted on the running system. Just used by
some systems to boot. And has no filesystem, either, thus can not be
mounted. It is "raw".

During Beta phase it was created on some systems that did not need it.


Summarizing: it's holding the machine's boot code which can find the system's
boot loader, like MBR did on MBR partitioned disks.

Correct me if that's not what it is.

Don't ask me... I got this second hand ;-)

I think it is the next stage after the MBR and before grub files stored
in /boot, which were previously stored in disk sectors after the MBR or
PBR. Space that was not officially assigned.

MBR --> core.img --> /boot/grub2/*

(PBR: partition boot record)

If I got this right, XFS partitions do not have this free space, and
thus having root on XFS need a separate /boot partition, or Grub in the MBR.

On GPT partitions there is an EFI partition and here I get lost. I think
that the firmware of the computer (UEFI mode) knows enough to read the
EFI partition FAT filesystem to read at least one file there, which then
decides what to do.

If the GPT disk is booting in legacy or BIOS mode, then there is a
Protective MBR, which may have a syslinux boot code that can boot the
partition marked bootable by loading that partition boot code sector. If
Grub is installed in PMBR then... missing info in my knowledge. I
*think* the bios part is then needed.

I can't fill this gap now, and I'm also hungry, so I'll leave :-)

Cheers / Saludos,

Carlos E. R.
(from 42.3 x86_64 "Malachite" at Telcontar)

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