.\"	$OpenBSD: getentropy.2,v 1.7 2014/12/10 19:19:00 schwarze Exp $
.\"
.\" Copyright (c) 2014 Theo de Raadt
.\" Copyright (c) 2015 Joyent, Inc.
.\"
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.Dd "Dec 31, 2014"
.Dt GETENTROPY 3C
.Os
.Sh NAME
.Nm getentropy
.Nd get entropy
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn getentropy "void *buf" "size_t buflen"
.Sh DESCRIPTION
.Nm
fills a buffer with high-quality entropy, which can be used
as input for process-context pseudorandom generators like
.Xr arc4random 3C .
.Pp
The maximum buffer size permitted is 256 bytes.
If
.Va buflen
exceeds this, an error of
.Er EIO
will be indicated.
.Pp
.Nm
is not intended for regular code; please use the
.Xr arc4random 3C
family of functions instead.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn getentropy
will succeed unless:
.Bl -tag -width Er
.It Er EFAULT
The
.Fa buf
parameter points to an
invalid address.
.It Er EIO
Too many bytes requested, or some other fatal error occurred.
.El
.Sh INTERFACE STABILITY
.Sy Comitted
.Sh MT-LEVEL
.Sy Async-Signal-Safe
.Sh SEE ALSO
.Xr arc4random 3C ,
.Xr attributes 7