Re: parted boot loader code?

[Chris Murphy]

This is parted-3.1-9.fc18.x86_64



On Dec 10, 2012, at 12:59 PM, Chris Murphy <address@hidden> wrote:

> What is, and why does parted insert ~80 bytes of code to the MBR boot loader 
> region of a disk when that region contains zeros?
> Example:
> 
> address@hidden liveuser]# dd if=/dev/sda count=1 2>/dev/null | hexdump -C
> 00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> *
> 00000200
> 
> ## LBA 0 is all zeros.
> 
> 
> address@hidden liveuser]# parted /dev/sda mklabel msdos
> Information: You may need to update /etc/fstab.
> 
> address@hidden liveuser]# dd if=/dev/sda count=1 2>/dev/null | hexdump -C
> 00000000  fa b8 00 10 8e d0 bc 00  b0 b8 00 00 8e d8 8e c0  |................|
> 00000010  fb be 00 7c bf 00 06 b9  00 02 f3 a4 ea 21 06 00  |...|.........!..|
> 00000020  00 be be 07 38 04 75 0b  83 c6 10 81 fe fe 07 75  |....8.u........u|
> 00000030  f3 eb 16 b4 02 b0 01 bb  00 7c b2 80 8a 74 01 8b  |.........|...t..|
> 00000040  4c 02 cd 13 ea 00 7c 00  00 eb fe 00 00 00 00 00  |L.....|.........|
> 00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> *
> 000001b0  00 00 00 00 00 00 00 00  64 0b 00 00 00 00 00 00  |........d.......|
> 000001c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> *
> 000001f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 55 aa  |..............U.|
> 00000200
> address@hidden liveuser]#
> 
> 
> ## LBA 0 now contains code were there was previously none. The problem with 
> it I'm encountering with a single BIOS so far (Virtual Box) is that this disk 
> is no longer skipped at boot time, the BIOS tries to boot from it and hangs.
> 
> 
> Chris Murphy
>