.\"	$OpenBSD: getentropy.2,v 1.10 2022/02/06 00:29:02 jsg Exp $
.\"
.\" Copyright (c) 2014 Theo de Raadt
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.Dd $Mdocdate: February 6 2022 $
.Dt GETENTROPY 2
.Os
.Sh NAME
.Nm getentropy
.Nd get entropy
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn getentropy "void *buf" "size_t buflen"
.Sh DESCRIPTION
.Fn getentropy
fills a buffer with high-quality entropy, which can be used
as input for process-context pseudorandom generators like
.Xr arc4random 3 .
.Pp
The maximum buffer size permitted is 256 bytes.
.Pp
.Fn getentropy
is not intended for regular code; use the
.Xr arc4random 3
family of functions instead.
.Pp
The high-quality entropy data is provided by the
.Xr random 4
subsystem.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn getentropy
will succeed unless:
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa buf
parameter points to an
invalid address.
.It Bq Er EIO
Too many bytes requested, or some other fatal error occurred.
.El
.Sh SEE ALSO
.Xr arc4random 3
.Sh HISTORY
The
.Fn getentropy
function appeared in
.Ox 5.6 .