NAME
getentropy – get entropy
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
int
getentropy(void *buf, size_t buflen);
DESCRIPTION
getentropy() fills a buffer with high-quality random data.
The maximum buflen permitted is 256 bytes.
If it does not produce an error, getentropy() always provides the requested number of bytes of random data.
Similar to reading from /dev/urandom just after boot, getentropy() may block until the system has collected enough entropy to seed the CSPRNG.
IMPLEMENTATION NOTES
The getentropy() function is implemented using getrandom(2).
RETURN VALUES
The getentropy() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORS
getentropy() will succeed unless:
- [EFAULT]
-
The buf parameter points to an invalid address.
- [EINVAL]
-
Too many bytes requested.
SEE ALSO
STANDARDS
getentropy() conforms to IEEE Std 1003.1-2024 (“POSIX.1”).
HISTORY
The getentropy() function appeared in OpenBSD 5.6. The FreeBSD libc compatibility shim first appeared in FreeBSD 12.0.