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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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getentropy(3) Library Functions Manual getentropy(3)
getentropy - fill a buffer with random bytes
Standard C library (libc, -lc)
#include <unistd.h>
int getentropy(void buffer[.length], 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 to indicate the error.
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.
None.
glibc 2.25. OpenBSD.
The getentropy() function is implemented using getrandom(2).
Whereas the glibc wrapper makes getrandom(2) a cancelation point,
getentropy() is not a cancelation 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)
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2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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Linux man-pages 6.9.1 2024-05-02 getentropy(3)
Pages that refer to this page: getrandom(2), random(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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