Re: Create files with specific sizes?

Simon Valiquette
2004-12-17T21:15:25Z

SVisor a écrit :
>
>>> I wanted a file of garbage, not zeroes.
>>> So I tried: dd if=/dev/random of=file bs=1k count=1024
>
> Nope I did not abort it, I just moved the mouse to generate more random
> numbers (with dd running in X terminal). What dd says is:
>
> 0+1024 records in
> 0+1024 records out
>

You have read and written 1024 partial blocks (ie. not complete).
Why? I don't know.

You did'nt say if the produced file is always the same size, or
differents but always bigger (or smaller) than 4K? Please give the
exact value(s) as it can hint at what the problem is. I have the
impression that you get only 4 bytes per block readed. You can
experiment with different values to try to find a patern.

Also, check if the produced file really is random data.

Try "cp /dev/urandom /tmp/file.cp" and type CTRL-C after waiting a
couple of seconds. If it works (and get a very big file), then the
problem is not related to the random devices. I suppose here that you
had the same problem with random and urandom.

By curiosity, try this and report the exact file size produced (and
check if it is random data).

dd if=/dev/urandom of=/tmp/file.cp bs=1 count=1024x1024

> But the file still is just ~4k. Maybe a bug?
>

Maybe, but I would be surprised. I suspect that if you do a
reinstall from scratch (or use a Knoppix disk) you will not see your
problem any more. You did'nt even said which Linux distribution you are
using, so with that little information I can't help much. By the way, I
can't reproduce your problem.

Simon Valiquette