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Old 11-27-2012, 08:23 AM   #1
froff
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Question What is exact grub2 stuff size beyond mbr?


hello
I wonder how many bytes grub2 puts into my hdd starting from MBR.
I found information, that core.img file is put after MBR (at 512 offset).
I found another information that kernel.img file is one of components of core.img.
But how can both be true if my kernel.img file is significally larger than core.img?

I'm asking because I use (with help of grub2tc) dual boot with truecrypted windows7 and truecrypt uses sector 63 (counting from 1) for it's volume header data. Grub2 overwrote this sector and I would like to get known if this area is realy used by it and if it is safe to re-overvrite it again with truecrypt original sector as described here:

http://gitorious.org/grub2tc/grub2tc.../master/README
 
Old 11-27-2012, 02:37 PM   #2
syg00
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I would be most surprised if grub2 uses sectors that far away from the MBR. But it might zero them - I have 20 sectors of zeroes from sector 40.
Should be safe enough to put the tc header back.

core.img would likely just locate kernel.img, not include it, although I haven't checked the code.
 
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Old 11-28-2012, 06:03 PM   #3
froff
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Quote:
Originally Posted by syg00 View Post
I would be most surprised if grub2 uses sectors that far away from the MBR. But it might zero them - I have 20 sectors of zeroes from sector 40.
Should be safe enough to put the tc header back.

core.img would likely just locate kernel.img, not include it, although I haven't checked the code.
Thank You for answer.
I looked into my dumped grub_mbr file and there is a lot of non-zero data at last kilobytes.
I put my tc header to sector 63 and everything looks to work properly but I'm still not sure if I can be sure

BTW: my core.img has about 26kB
 
  


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