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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
GETENTROPY(3) Linux Programmer's Manual GETENTROPY(3)
getentropy - fill a buffer with random bytes
#include <unistd.h>
int getentropy(void *buffer, size_t length);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getentropy():
_DEFAULT_SOURCE
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.
On success, this function returns zero. On error, -1 is returned,
and errno is set appropriately.
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.
The getentropy() function first appeared in glibc 2.25.
This function is nonstandard. It is also present on OpenBSD.
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.
getrandom(2), urandom(4), random(7)
This page is part of release 5.08 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)
Pages that refer to this page: getrandom(2) , random(7)
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