1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)rand.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd April 2, 2013 36.Dt RAND 3 37.Os 38.Sh NAME 39.Nm rand , 40.Nm srand , 41.Nm sranddev , 42.Nm rand_r 43.Nd bad random number generator 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In stdlib.h 48.Ft void 49.Fn srand "unsigned seed" 50.Ft void 51.Fn sranddev void 52.Ft int 53.Fn rand void 54.Ft int 55.Fn rand_r "unsigned *ctx" 56.Sh DESCRIPTION 57.Bf -symbolic 58The functions described in this manual page are not cryptographically 59secure. 60Cryptographic applications should use 61.Xr arc4random 3 62instead. 63.Ef 64.Pp 65These interfaces are obsoleted by 66.Xr random 3 . 67.Pp 68The 69.Fn rand 70function computes a sequence of pseudo-random integers in the range 71of 0 to 72.Dv RAND_MAX 73(as defined by the header file 74.In stdlib.h ) . 75.Pp 76The 77.Fn srand 78function sets its argument 79.Fa seed 80as the seed for a new sequence of 81pseudo-random numbers to be returned by 82.Fn rand . 83These sequences are repeatable by calling 84.Fn srand 85with the same seed value. 86.Pp 87If no 88.Fa seed 89value is provided, the functions are automatically 90seeded with a value of 1. 91.Pp 92The 93.Fn sranddev 94function initializes a seed using pseudo-random numbers obtained from the kernel. 95.Pp 96The 97.Fn rand_r 98function 99provides the same functionality as 100.Fn rand . 101A pointer to the context value 102.Fa ctx 103must be supplied by the caller. 104.Pp 105For better generator quality, use 106.Xr random 3 107or 108.Xr lrand48 3 . 109.Sh SEE ALSO 110.Xr arc4random 3 , 111.Xr lrand48 3 , 112.Xr random 3 , 113.Xr random 4 114.Sh STANDARDS 115The 116.Fn rand 117and 118.Fn srand 119functions 120conform to 121.St -isoC . 122.Pp 123The 124.Fn rand_r 125function is as proposed in the POSIX.4a Draft #6 document. 126