1.\" $OpenBSD: getentropy.2,v 1.9 2019/09/28 14:55:12 deraadt Exp $ 2.\" 3.\" Copyright (c) 2014 Theo de Raadt 4.\" 5.\" Permission to use, copy, modify, and distribute this software for any 6.\" purpose with or without fee is hereby granted, provided that the above 7.\" copyright notice and this permission notice appear in all copies. 8.\" 9.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16.\" 17.Dd $Mdocdate: September 28 2019 $ 18.Dt GETENTROPY 2 19.Os 20.Sh NAME 21.Nm getentropy 22.Nd get entropy 23.Sh SYNOPSIS 24.In unistd.h 25.Ft int 26.Fn getentropy "void *buf" "size_t buflen" 27.Sh DESCRIPTION 28.Fn getentropy 29fills a buffer with high-quality entropy, which can be used 30as input for process-context pseudorandom generators like 31.Xr arc4random 3 . 32.Pp 33The maximum buffer size permitted is 256 bytes. 34.Pp 35.Fn getentropy 36is not intended for regular code; please use the 37.Xr arc4random 3 38family of functions instead. 39.Pp 40The high-quality entropy data is provided by the 41.Xr random 4 42subsystem. 43.Sh RETURN VALUES 44.Rv -std 45.Sh ERRORS 46.Fn getentropy 47will succeed unless: 48.Bl -tag -width Er 49.It Bq Er EFAULT 50The 51.Fa buf 52parameter points to an 53invalid address. 54.It Bq Er EIO 55Too many bytes requested, or some other fatal error occurred. 56.El 57.Sh SEE ALSO 58.Xr arc4random 3 59.Sh HISTORY 60The 61.Fn getentropy 62function appeared in 63.Ox 5.6 . 64