GETENTROPY(3)

NAME
getentropy - get entropy

LIBRARY
libc

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

ERRORS
getentropy() will succeed unless:

[EFAULT]
    The buf parameter points to an invalid address.

[EINVAL]
    Too many bytes requested.

SEE ALSO
getrandom(2), arc4random(3), random(4)

STANDARDS
getentropy() conforms to p1003.1-2024.

HISTORY
The getentropy() function appeared in OpenBSD 5.6. The FreeBSD libc compatibility shim first appeared in FreeBSD 12.0.