GETENTROPY(3) Linux Programmer's Manual GETENTROPY(3)
NAME
getentropy - fill a buffer with random bytes
SYNOPSIS
#include <unistd.h>
int getentropy(void *buffer, size_t length);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getentropy():
_DEFAULT_SOURCE
DESCRIPTION
The getentropy() function writes length bytes of high-quality random
data to the buffer starting at the location pointed to by buffer. The
maximum permitted value for the length argument is 256.
A successful call to getentropy() always provides the requested number
of bytes of entropy.
RETURN VALUE
On success, this function returns zero. On error, -1 is returned, and
errno is set appropriately.
ERRORS
EFAULT Part or all of the buffer specified by buffer and length is not
in valid addressable memory.
EIO length is greater than 256.
EIO An unspecified error occurred while trying to overwrite buffer
with random data.
ENOSYS This kernel version does not implement the getrandom(2) system
call required to implement this function.
VERSIONS
The getentropy() function first appeared in glibc 2.25.
CONFORMING TO
This function is nonstandard. It is also present on OpenBSD.
NOTES
The getentropy() function is implemented using getrandom(2).
Whereas the glibc wrapper makes getrandom(2) a cancellation point,
getentropy() is not a cancellation point.
getentropy() is also declared in <sys/random.h>. (No feature test
macro need be defined to obtain the declaration from that header file.)
A call to getentropy() may block if the system has just booted and the
kernel has not yet collected enough randomness to initialize the en-
tropy pool. In this case, getentropy() will keep blocking even if a
signal is handled, and will return only once the entropy pool has been
initialized.
SEE ALSO
getrandom(2), urandom(4), random(7)
COLOPHON
This page is part of release 5.07 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 GETENTROPY(3)