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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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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 5.10 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)
Copyright and license for this manual page
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