Harm Yourself with rdev and Superficial Reading

Fast reading technique is good to get the idea from a long document, but the more you use it the more you get accustomed and the more you use it without notice. That’s bad especially when you are dealing with something potentially dangerous – explosives, driving directions, contracts and … man pages. So when reading the rdev man pages I didn’t read it too carefully and missed the difference between kernel image and boot device. It didn’t help that the man page examples are quite misleading using many times the /dev/fd0 as kernel image synonym.
The rdev command (on Linux) works by chaining pairs of bytes at specific offsets in the kernel image. The usage of rdev is deprecated (I read this on man page O:-), since it is based on historical legacy and works only for x86 architectures.
Likely I was thinking about the grub boot code instead of kernel, so I launched rdev on /dev/hda and… it changed two bytes at offset 506,507. What did that two bytes contain? For sure not 0xFFFD since I guess this is the main cause for the boot failure of the notebook.
I hope this evening to verify my theory and eventually restore my notebook health.

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