Strange booting problem

[jd1008]

On 06/26/2015 05:29 PM, Rick Stevens wrote:
> On 06/26/2015 04:05 PM, jd1008 wrote:
>>
>>
>> On 06/26/2015 04:55 PM, Gordon Messmer wrote:
>>> On 06/26/2015 02:51 PM, jd1008 wrote:
>>>> Just wondering about the bytes in the first sector which
>>>> you thought might be boot code that is confusing BIOS
>>>> to think that my usb drive is bootable.
>>>> The bytes you already saw are obviously not boot code.
>>>
>>> What is obvious to you is not obvious to the CPU, which simply
>>> executes instructions.  Everything in bytes is 0-446 is boot code,
>>> whether it does anything useful or not.
>> Fine! No argument there.
>> Where do device (or partition) labels reside? In the partitions?
>
> fdisk- (dos-) style partition tables do not have partition labels. GPT
> partitions do. They are 72 bytes long, starting at offset 56 in the
> partition's entry in the partition table.
>
> The location of the partition table is given in an 8-byte value
> starting at offset 72 in the GPT header. Generally, they start at the
> second LBA (LBA1) on the disk and are 128 bytes long.
>
> Filesystem labels (regardless of DPT or GPT partitioning) are located
> in the filesystem's superblock(s). They are 16 bytes long starting at
> offset 120 in each copy of the superblock.

OK. So if only GPT partitions have labels,
what does mlabel do (i.e. where does it place the label?).

$ yum provides /usr/bin/mlabel
Loaded plugins: langpacks, refresh-packagekit
mtools-4.0.18-4.fc20.x86_64 : Programs for accessing MS-DOS disks 
without mounting the disks
Repo        : fedora
Matched from:
Filename    : /usr/bin/mlabel