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Date: Thu, 11 Nov 2010 21:02:53 +0100
From: Matthias Apitz <guru@unixarea.de>
To: freebsd-questions@freebsd.org
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Subject: how to overwrite the content of a file
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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
-- 
Matthias Apitz
t +49-89-61308 351 - f +49-89-61308 399 - m +49-170-4527211
e <guru@unixarea.de> - w http://www.unixarea.de/