07-26-2016
/dev/random has a limitation - a good one. When the entropy pool is empty, it will not return values. It blocks on read(). /dev/urandom is the same as /dev/random except that when the entropy pool has no more values it will return a value anyway.
The entropy pool is a kernel-only readable object.
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rand(3UCB) SunOS/BSD Compatibility Library Functions rand(3UCB)
NAME
rand, srand - simple random number generator
SYNOPSIS
/usr/ucb/cc[ flag ... ] file ...
int rand()
int srand( seed);
unsigned seed;
DESCRIPTION
rand() uses a multiplicative congruential random number generator with period 2**32 to return successive pseudo-random numbers in the range
from 0 to "2**31 -1."
srand() can be called at any time to reset the random-number generator to a random starting point. The generator is initially seeded with a
value of 1.
SEE ALSO
drand48(3C), rand(3C), random(3C)
NOTES
Use of these interfaces should be restricted to only applications written on BSD platforms. Use of these interfaces with any of the system
libraries or in multi-thread applications is unsupported.
The spectral properties of rand() leave a great deal to be desired. drand48(3C) and random(3C) provide much better, though more elaborate,
random-number generators.
The low bits of the numbers generated are not very random; use the middle bits. In particular the lowest bit alternates between 0 and 1.
SunOS 5.10 12 Feb 1993 rand(3UCB)