1.\" $OpenBSD: getentropy.2,v 1.7 2014/12/10 19:19:00 schwarze Exp $ 2.\" 3.\" Copyright (c) 2014 Theo de Raadt 4.\" Copyright (c) 2015 Joyent, Inc. 5.\" 6.\" Permission to use, copy, modify, and distribute this software for any 7.\" purpose with or without fee is hereby granted, provided that the above 8.\" copyright notice and this permission notice appear in all copies. 9.\" 10.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 11.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 12.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 13.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 14.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 15.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 16.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 17.\" 18.Dd "Dec 31, 2014" 19.Dt GETENTROPY 3C 20.Os 21.Sh NAME 22.Nm getentropy 23.Nd get entropy 24.Sh SYNOPSIS 25.Fd #include <unistd.h> 26.Ft int 27.Fn getentropy "void *buf" "size_t buflen" 28.Sh DESCRIPTION 29.Nm 30fills a buffer with high-quality entropy, which can be used 31as input for process-context pseudorandom generators like 32.Xr arc4random 3C . 33.Pp 34The maximum buffer size permitted is 256 bytes. 35If 36.Va buflen 37exceeds this, an error of 38.Er EIO 39will be indicated. 40.Pp 41.Nm 42is not intended for regular code; please use the 43.Xr arc4random 3C 44family of functions instead. 45.Sh RETURN VALUES 46.Rv -std 47.Sh ERRORS 48.Fn getentropy 49will succeed unless: 50.Bl -tag -width Er 51.It Er EFAULT 52The 53.Fa buf 54parameter points to an 55invalid address. 56.It Er EIO 57Too many bytes requested, or some other fatal error occurred. 58.El 59.Sh INTERFACE STABILITY 60.Sy Comitted 61.Sh MT-LEVEL 62.Sy Async-Signal-Safe 63.Sh SEE ALSO 64.Xr arc4random 3C 65.Xr attributes 5 66