Strange booting problem

[jd1008]

On 07/02/2015 10:56 AM, Rick Stevens wrote:
> On 07/01/2015 02:39 PM, jd1008 wrote:
>>
>>
>> On 07/01/2015 03:14 PM, Matthew Woehlke wrote:
>>> On 2015-06-30 19:01, jd1008 wrote:
>>>> So, how can I proceed with a brand new drive,
>>>> dd /dev/zero into the first ... say 4K bytes, partition
>>>> it with fdisk, do not mark any partition bootable, so
>>>> that bios will skip over it ?
>>> Don't know why no one's mentioned this, but... you could always just
>>> install an actual bootloader on the drive that boots from the device
>>> from which you really want to boot. (I think you can do this with
>>> grub...)
>>>
>>> Of course, plugging that drive into any other computer might make 
>>> for an
>>> interesting experience :-).
>>>
>> I am sorry - but ...
>> the design and implementation of the traditional
>> (msdos) scheme and ( from what I understand so far
>> from all the respondents), even gpt, effectively render
>> the disk to have a signature which BIOS interprets
>> as a valid partition table AND as bootable, and thus
>> hangs there looking for what does not exist.
>>
>> Why the design mixed 2 different things into 1, I have
>> no idea. But AFAIAC, it sucks and blows atthe same time.
>>
>> Theoretically, supose I want my PC to have 2 identical drives,
>> partitioned identically, both bootable.
>> Say the boot order is cd-rom, drive A, then drive B.
>> CD-rom is empty, bios moves on to drive A. Somehow
>> drive A's boot code is corrupt (say somehow all nulled).
>> PC will never move on to drive B.
>>
>> So, instead of fixing the issue, we invent new, complex
>> schemes that require even more complex SW like VM's,
>> LVM's, .... etc etc.. to solve a problem created by a very
>> silly error: partitioned means bootable as far as BIOS
>> is concerned. At least, that is what I have come to understand
>> and experience (when I removed the boot signature bytes).
>
> Simply nulling bytes 510 and 511 of the first sector (getting rid
> of the boot signature) should make the BIOS ignore the drive. fdisk
> will complain that the partition table is invalid because of the
> invalid boot signature, but that's all. The rest of the drive should
> be functional and usable--just not bootable.
>
> Tagging a partition as "bootable" only affects Microsoft OSes. The
> boot loader itself doesn't care. What that boot loader loads and
> hands control to--THAT might care about the bootable flag. The Linux
> kernel ignores it.

Will try and get back to you.