NAME
random, urandom
— random data source
device
SYNOPSIS
#include
<sys/types.h>
#include <dev/rndvar.h>
DESCRIPTION
The urandom device produces high quality
pseudo-random output data without ever blocking, even immediately after
booting. Entropy data is collected from system activity (such as disk,
network, and clock device interrupts), and then used to key a stream cipher
to generate the output.
The urandom device is intended to be used
in scripts. In C programs, use the
arc4random(3) family of functions instead, which can be
called in almost all coding environments, including
pthreads(3),
chroot(2), and
pledge(2), and which avoids accessing a device every time.
Never use /dev/random. On OpenBSD, it does the same as /dev/urandom, but on many other systems, it misbehaves. For example, it may block, directly return entropy instead of using a stream cipher, or only return data from hardware random generators.
FILES
- /dev/urandom
SEE ALSO
HISTORY
A random device first appeared in Linux in
1994. The random and urandom
devices have been available since OpenBSD 2.0.
BUGS
No randomness testing suite provided.