how to overwrite the content of a file

[Matthias Apitz]

Hello,

What is the best method to overwrite the blocks of a given file with
bytes of 0x00, i.e. not to O_TRUNC away the blocks to the freelist of the
file system, but overwrite the old blocks?

I've checked

$ dd if=/dev/zero of=file count=4

but dd(1) opens the file with O_RDWR|O_CREAT|O_TRUNC which for sure will
give away the old blocks and adquire new blocks. Any idea?

The background of the question is that I want to make sure, that certain
content is not placed into a dump of the file system before give away
the output of the dump(8).

Thanks

	matthias
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Matthias Apitz
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