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.\" $OpenBSD: random.4,v 1.33 2017/11/10 23:29:09 naddy Exp $
.\"
.\" Copyright (c) 1996, 1997 Michael Shalayeff
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: November 10 2017 $
.Dt RANDOM 4
.Os
.Sh NAME
.Nm random ,
.Nm urandom
.Nd random data source device
.Sh SYNOPSIS
.In sys/types.h
.In dev/rndvar.h
.Sh DESCRIPTION
The
.Nm 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.
.Pp
The
.Nm urandom
device is intended to be used in scripts.
In C programs, use the
.Xr arc4random 3
family of functions instead, which can be called in almost all
coding environments, including
.Xr pthreads 3 ,
.Xr chroot 2 ,
and
.Xr pledge 2 ,
and which avoids accessing a device every time.
.Pp
Never use
.Pa /dev/random .
On
.Ox ,
it does the same as
.Pa /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.
.Sh FILES
.Bl -tag -width /dev/urandom -compact
.It Pa /dev/urandom
.El
.Sh SEE ALSO
.Xr arc4random 3 ,
.Xr amdpm 4 ,
.Xr glxsb 4 ,
.Xr pchb 4 ,
.Xr arc4random 9
.Sh HISTORY
A
.Nm
device first appeared in Linux in 1994.
The
.Nm random
and
.Nm urandom
devices have been available since
.Ox 2.0 .
.Sh BUGS
No randomness testing suite provided.
|
