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)