getentropy - fill a buffer with random bytes
int getentropy(void *buffer, size_t length);
Feature Test Macro Requirements for glibc (see feature_test_macros
() function writes length
bytes of high-quality
random data to the buffer starting at the location pointed to by
. The maximum permitted value for the length
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
is set appropriately.
- Part or all of the buffer specified by buffer and length is
not in valid addressable memory.
- length is greater than 256.
- An unspecified error occurred while trying to overwrite buffer with
- This kernel version does not implement the getrandom(2) system call
required to implement this function.
() function first appeared in glibc 2.25.
This function is nonstandard. It is also present on OpenBSD.
() function is implemented using getrandom
Whereas the glibc wrapper makes getrandom
(2) a cancellation point,
() is not a cancellation point.
() 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.