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So I'm using a board on a ramfs that is pretty much running a barebones Linux kernel that is pretty much just POSIX-compliant (with busybox). For some disk drive testing, I am trying to generate a large (on the order of a Gigabyte) random file.

Currently what I'm doing is as follows:

dd if=/dev/urandom of=./basefile bs=1M count=10
for i in {1..100}; do cat ./basefile >> ./testFile; done

Thus I have a practical solution that meets my needs.

However, on a more academic note, is there an efficient way to generate completely (psuedo-)random files using POSIX utilities only? Openssl is not installed. For the sake of comparison, above command runs in 23.5s, while below command runs in 3m3.179s:

dd if=/dev/urandom of=./testFile bs=1M count=1000
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You know urandom needs its entropy pool filled to be fast right? Don't just leave it idling away. – micke Nov 7 '12 at 21:52
@micke I thought that that was random (and urandom just looped over whatever random data it had or something like that). – Ross Aiken Nov 7 '12 at 21:54
@micke urandom doesn't care about entropy, you're confusing with /dev/random. – Renan Nov 7 '12 at 21:59

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