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Thread: [SOLVED] How to determine which Linux partition w/ Grub controls the MBR?

  1. #21
    Join Date
    Mar 2008
    Beans
    4,715
    Distro
    Ubuntu 9.10 Karmic Koala

    Re: [SOLVED] How to determine which Linux partition w/ Grub controls the MBR?

    Thanks once again meierfra..
    I don't actually know what bootloader is installed on the MBR -- the system had Ubuntu pre-installed. I'm guessing that it is the original Windows MBR.

    Code:
    % sudo dd if=/dev/sda   bs=512  count=1| hexdump -c
    1+0 records in
    1+0 records out
    512 bytes (512 B) copied, 2.8015e-05 seconds, 18.3 MB/s
    0000000   3 300 216 320 274  \0   | 216 300 216 330 276  \0   | 277  \0
    0000010 006 271  \0 002 374 363 244   P   h 034 006 313 373 271 004  \0
    0000020 275 276  \a 200   ~  \0  \0   |  \v 017 205 020 001 203 305 020
    0000030 342 361 315 030 210   V  \0   U 306   F 021 005 306   F 020  \0
    0000040 264   A 273 252   U 315 023   ]   r 017 201 373   U 252   u  \t
    0000050 367 301 001  \0   t 003 376   F 020   f   ` 200   ~ 020  \0   t
    0000060   &   f   h  \0  \0  \0  \0   f 377   v  \b   h  \0  \0   h  \0
    0000070   |   h 001  \0   h 020  \0 264   B 212   V  \0 213 364 315 023
    0000080 237 203 304 020 236 353 024 270 001 002 273  \0   | 212   V  \0
    0000090 212   v 001 212   N 002 212   n 003 315 023   f   a   s 036 376
    00000a0   N 021 017 205  \f  \0 200   ~  \0 200 017 204 212  \0 262 200
    00000b0 353 202   U   2 344 212   V  \0 315 023   ] 353 234 201   > 376
    00000c0   }   U 252   u   n 377   v  \0 350 212  \0 017 205 025  \0 260
    00000d0 321 346   d 350 177  \0 260 337 346   ` 350   x  \0 260 377 346
    00000e0   d 350   q  \0 270  \0 273 315 032   f   # 300   u   ;   f 201
    00000f0 373   T   C   P   A   u   2 201 371 002 001   r   ,   f   h  \a
    0000100 273  \0  \0   f   h  \0 002  \0  \0   f   h  \b  \0  \0  \0   f
    0000110   S   f   S   f   U   f   h  \0  \0  \0  \0   f   h  \0   |  \0
    0000120  \0   f   a   h  \0  \0  \a 315 032   Z   2 366 352  \0   |  \0
    0000130  \0 315 030 240 267  \a 353  \b 240 266  \a 353 003 240 265  \a
    0000140   2 344 005  \0  \a 213 360 254   <  \0   t 374 273  \a  \0 264
    0000150 016 315 020 353 362   + 311 344   d 353  \0   $ 002 340 370   $
    0000160 002 303   I   n   v   a   l   i   d       p   a   r   t   i   t
    0000170   i   o   n       t   a   b   l   e  \0   E   r   r   o   r    
    0000180   l   o   a   d   i   n   g       o   p   e   r   a   t   i   n
    0000190   g       s   y   s   t   e   m  \0   M   i   s   s   i   n   g
    00001a0       o   p   e   r   a   t   i   n   g       s   y   s   t   e
    00001b0   m  \0  \0  \0  \0   b   z 231  \0  \0  \0   H  \0  \0  \0 001
    00001c0 001  \0 336 376   ? 006   ?  \0  \0  \0  \b 267 001  \0  \0  \0
    00001d0 001  \a  \v 376 277 223   G 267 001  \0   M 022 240  \0 200  \0
    00001e0 201 224 203 376 377 377 224 311 241  \0 364 242   D   $  \0 376
    00001f0 377 377 005 376 377 377 210   l 346   $   9   j   \  \0   U 252
    0000200
    Your prediction was once again right on the money.
    Lines 17-19 say "GRUB Geometry Hard Disk Read Error":

    Code:
    % sudo dd if=/dev/sda3  bs=512  count=1| hexdump -c
    1+0 records in
    1+0 records out
    512 bytes (512 B) copied, 2.7703e-05 seconds, 18.5 MB/s
    0000000 353   H 220  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
    0000010  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
    *
    0000030  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0 003 002
    0000040 377  \0  \0 200 024   C 346  \b  \0  \b 372 220 220 366 302 200
    0000050   u 002 262 200 352   Y   |  \0  \0   1 300 216 330 216 320 274
    0000060  \0     373 240   @   |   < 377   t 002 210 302   R 276 177   }
    0000070 350   4 001 366 302 200   t   T 264   A 273 252   U 315 023   Z
    0000080   R   r   I 201 373   U 252   u   C 240   A   | 204 300   u 005
    0000090 203 341 001   t   7   f 213   L 020 276 005   | 306   D 377 001
    00000a0   f 213 036   D   | 307 004 020  \0 307   D 002 001  \0   f 211
    00000b0   \  \b 307   D 006  \0   p   f   1 300 211   D 004   f 211   D
    00000c0  \f 264   B 315 023   r 005 273  \0   p 353   } 264  \b 315 023
    00000d0   s  \n 366 302 200 017 204 352  \0 351 215  \0 276 005   | 306
    00000e0   D 377  \0   f   1 300 210 360   @   f 211   D 004   1 322 210
    00000f0 312 301 342 002 210 350 210 364   @ 211   D  \b   1 300 210 320
    0000100 300 350 002   f 211 004   f 241   D   |   f   1 322   f 367   4
    0000110 210   T  \n   f   1 322   f 367   t 004 210   T  \v 211   D  \f
    0000120   ;   D  \b   }   < 212   T  \r 300 342 006 212   L  \n 376 301
    0000130  \b 321 212   l  \f   Z 212   t  \v 273  \0   p 216 303   1 333
    0000140 270 001 002 315 023   r   * 214 303 216 006   H   |   ` 036 271
    0000150  \0 001 216 333   1 366   1 377 374 363 245 037   a 377   &   B
    0000160   | 276 205   } 350   @  \0 353 016 276 212   } 350   8  \0 353
    0000170 006 276 224   } 350   0  \0 276 231   } 350   *  \0 353 376   G
    0000180   R   U   B      \0   G   e   o   m  \0   H   a   r   d       D
    0000190   i   s   k  \0   R   e   a   d  \0       E   r   r   o   r  \0
    00001a0 273 001  \0 264 016 315 020 254   <  \0   u 364 303  \0  \0  \0
    00001b0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
    *
    00001f0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0   U 252
    0000200

  2. #22
    Join Date
    Apr 2008
    Beans
    3,317
    Distro
    Kubuntu 9.10 Karmic Koala

    Re: [SOLVED] How to determine which Linux partition w/ Grub controls the MBR?

    Did some googeling. Your MBR is the typical Vista MBR:
    http://www.multibooters.co.uk/mbr.html

    For some reason the output of hexdump swaps the order in each of the four letter blocks: Your output starts with

    c033 d08e


    the web page has it as

    33c0 8ed0

  3. #23
    Join Date
    Mar 2008
    Beans
    4,715
    Distro
    Ubuntu 9.10 Karmic Koala

    Re: [SOLVED] How to determine which Linux partition w/ Grub controls the MBR?

    I don't understand why, but if I type

    Code:
    sudo dd if=/dev/sda  bs=512  count=1 | hexdump -C
    rather than

    Code:
    sudo dd if=/dev/sda  bs=512  count=1 | hexdump
    I get the Vista MBR signature exactly, without the pairs of hex digits swapped.

  4. #24
    Join Date
    Apr 2008
    Location
    Southern California, USA
    Beans
    Hidden!
    Distro
    Ubuntu Development Release

    Re: [SOLVED] How to determine which Linux partition w/ Grub controls the MBR?

    Quote Originally Posted by unutbu View Post
    I don't understand why, but if I type

    Code:
    sudo dd if=/dev/sda  bs=512  count=1 | hexdump -C
    rather than

    Code:
    sudo dd if=/dev/sda  bs=512  count=1 | hexdump
    I get the Vista MBR signature exactly, without the pairs of hex digits swapped.
    Here's a footnote from this Wiki
    ^ 1. On all IBM PC, PC compatible or any other little-endian computers, hexadecimal numbers of two or more bytes are always stored on media or in memory in reverse order (for more efficient CPU processing). Thus, the hex number 0xAA55 (or AA55h) will appear in a disk editor as the sequence: 55 AA.

    Mine are not swapped either.

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