.\"	$OpenBSD: getentropy.2,v 1.11 2024/08/02 01:53:21 guenther Exp $
.\"
.\" Copyright (c) 2014 Theo de Raadt
.\"
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.Dd $Mdocdate: August 2 2024 $
.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
.Dv GETENTROPY_MAX
(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 EINVAL
Too many bytes requested.
.El
.Sh SEE ALSO
.Xr arc4random 3
.Sh STANDARDS
The
.Fn getentropy
function conforms to
.St -p1003.1-2024 .
.Sh HISTORY
The
.Fn getentropy
function appeared in
.Ox 5.6 .