GETENTROPY
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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 entropy 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 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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