I recently heard that in Linux, /dev/random and /dev/urandom are pseudo random number generators but not true random number generator.

So I am curious to know the difference between pseudo & true random number? In other words What is the difference between pseudo-randomness & true-randomness?

  • 7
    $\begingroup$ This could largely be answered by a Google search. Do you have a more specific question about this related to computational science? $\endgroup$
    – horchler
    Mar 25, 2016 at 15:07
  • $\begingroup$ @horchler If this question is more suitable on other (SE) site (example-Unix & Linux) then tell/suggest me $\endgroup$
    – Pandya
    Mar 29, 2016 at 5:09
  • $\begingroup$ Wikipedia article Pseudorandom number generator $\endgroup$
    – Steve
    May 26, 2016 at 10:51

1 Answer 1


Most random numbers are in fact pseudo-random: they use a seed that is fed to a perfectly deterministic algorithm which can then generate series of numbers which are periodic but with a very large and complicated period so they usually appear random.

This has drawbacks of course since it's not really random, but also advantages, among which is reproducibility: if you store the seed, using this seed again will give you the exact same list of "random" numbers...

Here are a few links as well as another to a source of real random numbers

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    $\begingroup$ Conversely, for certain applications (generation of cryptographic keys, picking winning lottery numbers, etc.) it's very important that the output of a random number generator be unpredictable. In cryptographic applications it's common to combine actual physically random numbers with a pseudorandom number generator to produce unpredicatable output. $\endgroup$ Apr 26, 2016 at 2:24

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