GETENTROPY(3) Linux Programmer's Manual GETENTROPY(3)
getentropy - fill a buffer with random bytes
int getentropy(void *buffer, size_t length);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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
getrandom(2), urandom(4), random(7)
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Linux 2017-09-15 GETENTROPY(3)
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