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Unable to boot BIOS/GPT system.

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  Unable to boot BIOS/GPT system. Daniel Fishman <quantera@gmail.com> - 2018-11-22 19:30 +0100
    Re: Unable to boot BIOS/GPT system. Daniel Fishman <quantera@gmail.com> - 2018-11-22 20:10 +0100
      Re: Unable to boot BIOS/GPT system. Georgi Naplatanov <gosho@oles.biz> - 2018-11-22 20:40 +0100
        Re: Unable to boot BIOS/GPT system. Daniel Fishman <quantera@gmail.com> - 2018-11-22 21:40 +0100
    Re: Unable to boot BIOS/GPT system. Georgi Naplatanov <gosho@oles.biz> - 2018-11-22 20:10 +0100
    Re: Unable to boot BIOS/GPT system. Steve McIntyre <steve@einval.com> - 2018-11-22 20:30 +0100
      Re: Unable to boot BIOS/GPT system. Daniel Fishman <quantera@gmail.com> - 2018-11-22 21:30 +0100
        Re: Unable to boot BIOS/GPT system. Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-11-23 07:40 +0100
          Re: Unable to boot BIOS/GPT system. "Thomas Schmitt" <scdbackup@gmx.net> - 2018-11-23 09:20 +0100
            Re: Unable to boot BIOS/GPT system. Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-11-23 21:10 +0100
      Re: Unable to boot BIOS/GPT system. Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-11-23 00:10 +0100

#202685 — Unable to boot BIOS/GPT system.

Hello,

I am trying to install Debian on a 4TB external HDD. Since I want
to boot the HDD (also) on old systems which support only BIOS,
and since the HDD is larger than 2TB, I decided to go with GPT
partition table and BIOS boot (or, in other words: BIOS/GTP).
I partitioned the HDD accordingly (see the details below), and
installed Debian. During a pre-installation configuration the
installer recognized BIOS boot partition, I configured the root
partition as ext4 and installed grub into the disk's MBR. But
when (after an installation) I am trying to boot the HDD, I receive
an error message: 'error: unknown filesystem' and drop into a
grub rescue mode.

What is the problem here and how it can be solved? It seems as
though grub's Stage 1.5 loader (that is - core.img, which is
supposed to be embedded in BIOS boot partition) doesn't contain
modules needed to read ext4 filesystem, which seems very strange.


Following are a bit more details about the partitions:

I used the following command to partition the HDD:

parted -s /dev/sdb mklabel gpt mkpart BIOS_boot ext2 1MiB 2MiB \
   mkpart swap linux-swap 2MiB 16000MiB mkpart data ext2 16000MiB 100% \
   set 1 bios_grub

[root@arch]# parted /dev/sdb unit MiB print
Model: WD Elements 25A1 (scsi)
Disk /dev/sdb: 3815415MiB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags:

Number  Start     End         Size        File system     Name  Flags
  1      1.00MiB   2.00MiB     1.00MiB                           bios_grub
  2      2.00MiB   16000MiB    15998MiB    linux-swap(v1)
  3      16000MiB  3815414MiB  3799414MiB


Debian's installation was done on x64 BIOS-only system.

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#202688

> 
> Hi Daniel,
> 
> in case of BIOS and GPT you have to create a partition for second stage
> of GRUB. If I can remember correctly its size should be less than 50MB.
> 
> HTH
> 
> Kind regards
> Georgi

I created it - this is the first partition (the one with bios_grub flag).
I did things similarly to the description here: https://bit.ly/2utVdNr

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#202691

On 11/22/18 9:08 PM, Daniel Fishman wrote:
> 
>>
>> Hi Daniel,
>>
>> in case of BIOS and GPT you have to create a partition for second stage
>> of GRUB. If I can remember correctly its size should be less than 50MB.
>>
>> HTH
>>
>> Kind regards
>> Georgi
> 
> I created it - this is the first partition (the one with bios_grub flag).
> I did things similarly to the description here: https://bit.ly/2utVdNr

Can you try to create all the partitions through Debian's installer. I
have a suspicion that partition type may be wrong for BIOS partition.

You have specified ext2 as file system for BIOS grub which may mean
Linux partition instead of BIOS grub partition (ef02 BIOS boot).

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#202697

> Can you try to create all the partitions through Debian's installer. I
> have a suspicion that partition type may be wrong for BIOS partition.
> 
> You have specified ext2 as file system for BIOS grub which may mean
> Linux partition instead of BIOS grub partition (ef02 BIOS boot).
> 

In the end, it was actually the lack of /boot partition that caused
the problem (as Steve McIntyre explained in another message in this thread).

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#202689

On 11/22/18 8:24 PM, Daniel Fishman wrote:
> Hello,
> 
> I am trying to install Debian on a 4TB external HDD. Since I want
> to boot the HDD (also) on old systems which support only BIOS,
> and since the HDD is larger than 2TB, I decided to go with GPT
> partition table and BIOS boot (or, in other words: BIOS/GTP).
> I partitioned the HDD accordingly (see the details below), and
> installed Debian. During a pre-installation configuration the
> installer recognized BIOS boot partition, I configured the root
> partition as ext4 and installed grub into the disk's MBR. But
> when (after an installation) I am trying to boot the HDD, I receive
> an error message: 'error: unknown filesystem' and drop into a
> grub rescue mode.
> 
> What is the problem here and how it can be solved? It seems as
> though grub's Stage 1.5 loader (that is - core.img, which is
> supposed to be embedded in BIOS boot partition) doesn't contain
> modules needed to read ext4 filesystem, which seems very strange.
> 
> 
> Following are a bit more details about the partitions:
> 
> I used the following command to partition the HDD:
> 
> parted -s /dev/sdb mklabel gpt mkpart BIOS_boot ext2 1MiB 2MiB \
>   mkpart swap linux-swap 2MiB 16000MiB mkpart data ext2 16000MiB 100% \
>   set 1 bios_grub
> 
> [root@arch]# parted /dev/sdb unit MiB print
> Model: WD Elements 25A1 (scsi)
> Disk /dev/sdb: 3815415MiB
> Sector size (logical/physical): 512B/4096B
> Partition Table: gpt
> Disk Flags:
> 
> Number  Start     End         Size        File system     Name  Flags
>  1      1.00MiB   2.00MiB     1.00MiB                           bios_grub
>  2      2.00MiB   16000MiB    15998MiB    linux-swap(v1)
>  3      16000MiB  3815414MiB  3799414MiB
> 
> 
> Debian's installation was done on x64 BIOS-only system.
> 


Hi Daniel,

in case of BIOS and GPT you have to create a partition for second stage
of GRUB. If I can remember correctly its size should be less than 50MB.

HTH

Kind regards
Georgi

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#202690

quantera@gmail.com wrote:
>
>I am trying to install Debian on a 4TB external HDD. Since I want
>to boot the HDD (also) on old systems which support only BIOS,
>and since the HDD is larger than 2TB, I decided to go with GPT
>partition table and BIOS boot (or, in other words: BIOS/GTP).
>I partitioned the HDD accordingly (see the details below), and
>installed Debian. During a pre-installation configuration the
>installer recognized BIOS boot partition, I configured the root
>partition as ext4 and installed grub into the disk's MBR. But
>when (after an installation) I am trying to boot the HDD, I receive
>an error message: 'error: unknown filesystem' and drop into a
>grub rescue mode.
>
>What is the problem here and how it can be solved? It seems as
>though grub's Stage 1.5 loader (that is - core.img, which is
>supposed to be embedded in BIOS boot partition) doesn't contain
>modules needed to read ext4 filesystem, which seems very strange.

...

>Number  Start     End         Size        File system     Name  Flags
>  1      1.00MiB   2.00MiB     1.00MiB                           bios_grub
>  2      2.00MiB   16000MiB    15998MiB    linux-swap(v1)
>  3      16000MiB  3815414MiB  3799414MiB

I'd expect that Grub won't be able to reliably work with that setup -
partition 3 goes past the 2TB mark, so the BIOS won't be able to map
it properly. Don't forget, when grub is reading the disk all it can
rely on are BIOS calls. Add yourself a small-ish /boot partition first
and you may be OK.

-- 
Steve McIntyre, Cambridge, UK.                                steve@einval.com
"Further comment on how I feel about IBM will appear once I've worked out
 whether they're being malicious or incompetent. Capital letters are forecast."
 Matthew Garrett, http://www.livejournal.com/users/mjg59/30675.html

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#202696

> 
> I'd expect that Grub won't be able to reliably work with that setup -
> partition 3 goes past the 2TB mark, so the BIOS won't be able to map
> it properly. Don't forget, when grub is reading the disk all it can
> rely on are BIOS calls. Add yourself a small-ish /boot partition first
> and you may be OK.
> 

Thanks, indeed this was the problem - after adding a boot partition
the HDD now boots on BIOS-only machines. Unfortunately, it does not
boot on UEFI machines. Seems that I have to start experimenting with
hybrid UEFI+BIOS boot...

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#202704

Le 22/11/2018 à 21:24, Daniel Fishman a écrit :
>>
>> I'd expect that Grub won't be able to reliably work with that setup -
>> partition 3 goes past the 2TB mark, so the BIOS won't be able to map
>> it properly. Don't forget, when grub is reading the disk all it can
>> rely on are BIOS calls. Add yourself a small-ish /boot partition first
>> and you may be OK.
> 
> Thanks, indeed this was the problem - after adding a boot partition
> the HDD now boots on BIOS-only machines.

So these machines have a broken BIOS implementation.

> Unfortunately, it does not boot on UEFI machines.

Of course not. EFI boot requires a FAT-formatted EFI partition and 
grub-efi-{amd64|ia32} depending on the firmware architecture (not the CPU).

If the EFI firmware can boot in legacy BIOS compatibility mode, it may 
require to set the boot flag on the protective GPT partition entry in 
the protective MBR. Use parted disk_set pmbr_boot or fdisk -t dos.

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#202705

Hi,

Pascal Hambourg wrote:
> If the EFI firmware can boot in legacy BIOS compatibility mode, it may
> require to set the boot flag on the protective GPT partition entry in the
> protective MBR.

According to user reports on grub-devel mailing list about grub-mkrescue
ISOs, the boot flag must not be set on the protective MBR partition.
But some BIOS implementations wont't regard the medium as bootable if there
is no boot flag set at all.

The compromise that finally worked for those who tested, was to create an
MBR partition of type 0x00 starting at LBA 0, having only one block, and
bearing the boot flag.
The tested EFIs and operating systems still recognized GPT if an additional
partiton of type 0x00 was present. But doubts remain. YMMV.

The decision with grub-mkrescue was to omit the boot flag by default
and to leave it to the user whether add-on xorrisofs option
--mbr-force-bootable shall cause the boot flag to be set on a dummy
partition.


Have a nice day :)

Thomas

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#202741

Le 23/11/2018 à 09:11, Thomas Schmitt a écrit :
> 
> Pascal Hambourg wrote:
>> If the EFI firmware can boot in legacy BIOS compatibility mode, it may
>> require to set the boot flag on the protective GPT partition entry in the
>> protective MBR.
> 
> According to user reports on grub-devel mailing list about grub-mkrescue
> ISOs, the boot flag must not be set on the protective MBR partition.

Yes, the protective partition should have the boot flag cleared for 
compliance with the GPT specification. But that's the theory, and there 
is the practice. For example I have come across an UEFI firmware 
implementation on a very old Intel board which required the boot flag to 
be cleared for EFI boot but set for legacy BIOS boot...

> But some BIOS implementations wont't regard the medium as bootable if there
> is no boot flag set at all.

IME, many Dell and HP's are among these.

> The compromise that finally worked for those who tested, was to create an
> MBR partition of type 0x00 starting at LBA 0, having only one block, and
> bearing the boot flag.

Indeed it worked for me too, and even allowed booting either in EFI or 
BIOS mode with the above board. At least until parted (or, I guess, any 
other libparted-based partition manager such as partman, the 
partitioning program part of the Debian installer) is used on the disk 
and resets the partition table to a standard protective MBR. Same if you 
set up a hybrid MBR with gdisk. So make sure to never use parted & Co. 
on such a disk or make sure you set the boot flag again afterwards.

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#202700

Le 22/11/2018 à 20:19, Steve McIntyre a écrit :
> quantera@gmail.com wrote:
>>
>> I am trying to install Debian on a 4TB external HDD. Since I want
>> to boot the HDD (also) on old systems which support only BIOS,
>> and since the HDD is larger than 2TB, I decided to go with GPT
>> partition table and BIOS boot (or, in other words: BIOS/GTP).
>> I partitioned the HDD accordingly (see the details below), and
>> installed Debian. During a pre-installation configuration the
>> installer recognized BIOS boot partition, I configured the root
>> partition as ext4 and installed grub into the disk's MBR. But
>> when (after an installation) I am trying to boot the HDD, I receive
>> an error message: 'error: unknown filesystem' and drop into a
>> grub rescue mode.
>>
>> What is the problem here and how it can be solved? It seems as
>> though grub's Stage 1.5 loader (that is - core.img, which is
>> supposed to be embedded in BIOS boot partition) doesn't contain
>> modules needed to read ext4 filesystem, which seems very strange.
> 
> ...
> 
>> Number  Start     End         Size        File system     Name  Flags
>>   1      1.00MiB   2.00MiB     1.00MiB                           bios_grub
>>   2      2.00MiB   16000MiB    15998MiB    linux-swap(v1)
>>   3      16000MiB  3815414MiB  3799414MiB
> 
> I'd expect that Grub won't be able to reliably work with that setup -
> partition 3 goes past the 2TB mark, so the BIOS won't be able to map
> it properly. Don't forget, when grub is reading the disk all it can
> rely on are BIOS calls. Add yourself a small-ish /boot partition first
> and you may be OK.

The limit of EDD BIOS calls which uses 64 bit LBA addressing is way 
beyond 2 TiB. But that specific BIOS implementation may be broken and 
unable to read beyond that limit. So indeed a boot or root partition at 
the beginning of the disk may help.

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