partition signature !=55AA

B

balanga

In the process of trying to create a DOS bootable USB stick I ended up with the above mentioned error msg.

Has anyone seen such a thing? I'm assuming that the problem is that the mbr does not end with 55AA.

If that is the case can I just copy the mbr to a file, change the last two bytes, and copy it back?
 
balanga said:
If that is the case can I just copy the mbr to a file, change the last two bytes, and copy it back?
Click to expand...
What makes you think that the damage is exactly the last two bytes? Given that the MBR is written as a 512-byte sector, it's actually likely that the other 510 bytes are also damaged. Do you have any idea how this happened? Do you even know what you were doing when it happened? Can you verify that the rest of the MBR is OK, before messing with the signature?
 
It’s a while since I’ve done things like this but I don’t think that tools like fdisk will work on the partition table unless they see the 55aa signature.
 
ralphbsz said:
What makes you think that the damage is exactly the last two bytes? Given that the MBR is written as a 512-byte sector, it's actually likely that the other 510 bytes are also damaged. Do you have any idea how this happened? Do you even know what you were doing when it happened? Can you verify that the rest of the MBR is OK, before messing with the signature?
Click to expand...
When you are trying achieve something and it doesn't work out as planned you try various things, so can't say for sure exactly how it happened, but it may have been when I tried running (DOS) sys.com create a bootable system on another device.

In the end I found a solution to sort out the above error:

Bash: 
gpart set -a active -i 1 da0

I can't explain how or why it worked but I stopped getting this error.

However, shortly afterwards, the same USB stick became completely unusable. It shows up on the BIOS boot menu and FreeBSD reports its existence when bootinfg but gpart doesn't see it, although camcontrol devlist shows it as (da0,pass1) so have no idea what is wrong with it or if it can be fixed.
 
Cath O'Deray said:
Lazy guess: an intermittent or worsening hardware issue with the drive.
Click to expand...
That's what I thought initially because it is pretty old, but by chance I ran

gpart create -s mbr da0

on the drive and I was able to access it again. Windows was completely unable to see it previously, so I thought it must have become damaged.
 
balanga said:
on the drive and I was able to access it again. Windows was completely unable to see it previously, so I thought it must have become damaged.
Click to expand...
In Windows, you can try to fix it:
open the cmd, run as administrator;
then run the command diskpart;
list disk;
select disk (select the disk you need);
clean.
Then, you create a new partition. Now, you can create again a bootable usb stick.
 
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