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Date: Sat, 23 May 2009 20:59:06 -0400 From: Bill Davidsen <davidsen@....com> To: Jon <jg@...k.org> CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, linux-kernel@...r.kernel.org Subject: Re: dd if=/dev/random of=data.bin bs=512 count=1 Jon wrote: > Hello KOSAKI, > > Thank you for your reply. > > KOSAKI Motohiro wrote: >>> Hello >>> >>> Issuing this command, I expected to get a file 4096 bytes in size. >>> Could someone let me know if I have missed something..? Or is there a >>> problem with using /dev/random this way? >>> >>> if I have a count=10 it hangs forever (several hours). >>> >>> Changing to use /dev/urandom and it generates the file ok. >> >> you already have the answer. /dev/random might blocked, /dev/urandom >> doesn't. > > Is this a "feature" of /dev/random ? ..it does not seem very useful to > have it able to block for so long. > Of course. /dev/random generates better random numbers (in the sense of less predictable), while /dev/urandom gives you some pseudo-random bits, which mat or may not be appropriate for your task. For timing disk speed /dev/zero is faster and less overhead. > Please include my email address in replies, as I'm not a member of this > list. > > Best regards, Jon -- Bill Davidsen <davidsen@....com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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