Section (3) getentropy
Name
getentropy — fill a buffer with random bytes
Synopsis
#include <unistd.h>
int
getentropy( |
void *buffer, |
size_t length) ; |
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Note | ||
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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
andlength
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.
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.
COLOPHON
This page is part of release 4.16 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/.
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