Strange booting problem

[jd1008]

Here is what happened after the 2 bytes at offset 511 and 512 were null'ed:

fdisk /dev/sdb

Welcome to fdisk (util-linux 2.24.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.

Created a new DOS disklabel with disk identifier 0x2c945747.

Command (m for help): p

Disk /dev/sdb: 1.8 TiB, 2000398933504 bytes, 3907029167 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 33553920 bytes
Disklabel type: dos
Disk identifier: 0x2c945747


So, you see, those 2 bytes must have also been encoded to contain
something about the partitions.

So, with this kind of change, it destroys the partition table.



On 06/30/2015 04:19 PM, Rick Stevens wrote:
> On 06/30/2015 03:17 PM, jd1008 wrote:
>> The link you refer to
>> talks about the 2 bytes past byte 255, they they are
>> bytes 256 and 257.
>
> No, you set the block size to 2, so you are seeking (2 * 255) or 512
> bytes into the disk.
>
>> But I already indicated the 466 bytes are null... in another usb drive I
>> tested,
>> thus no boot signature - and yet, bios hung forever because that disk
>> was 2nd
>> in boot order after cd/dvd drive, and before internal HD.
>>
>> So, the laptop's BIOS is executing what? A good code for moving from 
>> disk
>> to disk until it finds the bootable drive in the boot sequence 
>> specified?
>> Clearly in this case - it does not do so.
>> And yet, you insist it is not a flaw.
>>
>>
>> On 06/30/2015 03:47 PM, Gordon Messmer wrote:
>>> On 06/30/2015 02:28 PM, jd1008 wrote:
>>>> I already explained to you
>>>> 1. The disk is partitioned using fdisk.
>>>> 2. I cleared the 446 bytes to nulls.
>>>> 3. None of the partitions have a boot signature.
>>>
>>> The boot signature is at bytes 511 and 512, and you indicated that it
>>> is present:
>>> https://lists.fedoraproject.org/pipermail/users/2015-June/462295.html
>>>
>>> Those bytes indicate to BIOS that the disk contains boot code.  I
>>> tested wiping those bytes and verified that SeaBIOS, at least, will
>>> not attempt to run the boot sector of a disk after they are wiped.
>>>
>>>> You comment "bug" is not a word for "something I don't understand" or
>>>> "something I don't like."
>>>> is so totally irrelevant to what I have already reported wrt the
>>>> drive at hand and the BIOS at hand.
>>>> Such comments are sounding more and more like coming from an a*al
>>>> attitude!!
>>>
>>> Computers are just machines that execute instructions.  They don't
>>> reason.  They don't make decisions.  Their design may not always be
>>> the one you like, but that's not the same as being "buggy".
>>>
>>> I'm trying to reasonably explain and demonstrate that you can predict
>>> and control the computer's behavior, while you rant about Dell
>>> "f***ing up."  I think your anger is unjustified, both toward your
>>> system's vendor and toward me.  Maybe mellow out a little.
>>
>
>