Updated: 2020/Jul/29


GETENTROPY(3)              Library Functions Manual              GETENTROPY(3)

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.

SEE ALSO
     arc4random(3), rnd(4)

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.

NetBSD 9.99                       May 1, 2020                      NetBSD 9.99