Re: dd / netcat / md5sums: hashes do not match

From: Mark Hittinger (bugs_at_pu.net)
Date: 09/21/03

  • Next message: punk: "IDS&Firewall" 
    Date: Sun, 21 Sep 2003 03:21:22 GMT

    Casper H.S. *** <Casper.***@Sun.COM> writes:
    >>Casper H.S. *** <Casper.***@Sun.COM> writes:
    >>>>B# nc -l -p 6789 | dd of=./hda1.img bs=512 conv=noerror,sync
    >>>>A# dd if=/dev/hda1 bs=512 conv=noerror,sync | nc <B's IP> 6789

    >But you should *NEVER* use sync on pipes; the above usage is just wrong
    >(that is, the writing with "sync" is wrong as you read from a pipe; reading
    >the "disk" with sync is fine)

    Now thats interesting Casper thanks for mentioning it. In the above
    scenario (lets assume /dev/hda1 has bad spots) can we safely do this:

        dd if=/dev/hda1 bs=512 conf=noerror,sync | nc -->
    --> nc | dd of=./hda1.img obs=512

    When I say safely I'm excluding the damage to the file system from the
    bad spots - safely here means just keeping the good blocks "in order".

    I'm curious because someday I might just need to use such a trick while
    praying that no bad spot is a double indirect block :-)

    Thanks

    Mark Hittinger
    bugs@pu.net

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