[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: The backup GPT table is corrupt

On 8/12/25 14:31, mick.crane wrote:

On 2025-08-12 16:20, Thomas Schmitt wrote:

Hi,

mick.crane wrote:

0000000 45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00
0000020 cc c9 67 f5 00 00 00 00 af 4b f9 0d 00 00 00 00
0000040 01 00 00 00 00 00 00 00 22 00 00 00 00 00 00 00
0000060 8e 4b f9 0d 00 00 00 00 b6 c0 c0 ce 33 a9 6a 42
0000100 92 1b 04 bd a9 9e 80 8b 8f 4b f9 0d 00 00 00 00
0000120 80 00 00 00 80 00 00 00 00 00 00 00 00 00 00 00
0000140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00


The CRC "cc c9 67 f5" is indeed wrong. It should be "38 1c d4 e9".

I am quite sure that gdisk can compute the right checksum.
So the riddle is why it did not write it into the last block of the
disk.


Experiment proposal if you have really strong nerves:

You could alter these 4 bytes to e.g. "00 00 00 00" on the disk and
verify that gdisk does not write the bytes "cc c9 67 f5" during a new
attempt to repair the block.
1: I've got another PC and two of those StarTech USB things can attach different disks to. What's the incantation to copy this problem disk to another of similar size and have it boot?
The canonical old-school tool is dd(1). Be extremely careful of typographical and off-by-one errors when specifying device nodes, sector counts, etc.. I wrapped it up in a Perl script to do entire disks for monthly image backups.
Clonezilla is the canonical imaging/ cloning FOSS live (Linux?) distribution. It has many useful features and an console text Ui (ncurses?): 

https://www.clonezilla.org/
2: A decade ago I think I used some hex editor to change numbers on a wireless dongle that apparently were what tied it to one provider. What program to use to edit the backup GPT table? 


STFW hexedit(1) looks like the canonical old-school tool.
I'll try the different entries in the BIOS and see if there is any difference. 

mick



Document all of your Setup settings before you start.
My practice is to reset to factory defaults, find the minimum set of changes needed, make those changes, and document the changes. With EUFI, you will need to add boot entries for whatever OS's you have on disk. 


David
Reply to: