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RANDOM(4) Device Drivers Manual RANDOM(4)

random, arandom
random data source devices

#include <sys/types.h>
#include <dev/rndvar.h>

The various random devices produce high quality random output data. Entropy data is collected from system activity (like disk, network, and clock device interrupts and such), and then run through various hash or message digest functions to generate the output. All the random devices are expected to provide high quality pseudo-random output data.
The arc4random(3) function in userland libraries seeds itself from this device (or with the sysctl(3) interface), providing a second level of ARC4 hashed data without the need to access these devices every time.

/dev/random
 
/dev/arandom
 

arc4random(3), md5(3), random(3), amdpm(4), glxsb(4), pchb(4), arc4random(9), md5(9)

A random device first appeared in the Linux operating system. This is a cloned interface.
ARC4 routines added by David Mazieres.

No randomness testing suite provided.
January 11, 2011 OpenBSD-5.4