NAME

getentropy —

fill a buffer with high quality random data

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <unistd.h>

int
getentropy(void *buf, size_t buflen);

DESCRIPTION

The getentropy() function fills a buffer with high quality random data, suitable for seeding cryptographically secure pseudo-random number generators.

getentropy() is only intended for seeding random number generators and is not intended for use by regular code which simply needs secure random data. For this purpose, please use arc4random(3).

The maximum value for buflen is 256 bytes.

IMPLEMENTATION NOTES

getentropy() reads from the sysctl(7) variable kern.arandom.

RETURN VALUES

The getentropy() function returns 0 on success, and -1 if an error occurred.

ERRORS

getentropy() will succeed unless:

[EFAULT]: The buf argument points to an invalid memory address.
[EIO]: Too many bytes were requested.

STANDARDS

The getentropy() function is non-standard.

HISTORY

The getentropy() function first appeared in OpenBSD 5.6, then in FreeBSD 12.0, and NetBSD 10.