NAME

     getrandom — get random data

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/random.h>

     ssize_t
     getrandom(void *buf, size_t buflen, unsigned int flags);

DESCRIPTION

     getrandom() fills buf with up to buflen bytes of random data.

     The flags argument may include zero or more of the following:

     ‘GRND_NONBLOCK’  Return EAGAIN instead of blocking, if the random(4) device has not yet been
                      seeded.  By default, getrandom() will block until the device is seeded.

     ‘GRND_RANDOM’    This flag does nothing on FreeBSD.  /dev/random and /dev/urandom are
                      identical.

     If the random(4) device has been seeded, reads of up to 256 bytes will always return as many
     bytes as requested and will not be interrupted by signals.

RETURN VALUES

     Upon successful completion, the number of bytes which were actually read is returned.  For
     requests larger than 256 bytes, this can be fewer bytes than were requested.  Otherwise, -1
     is returned and the global variable errno is set to indicate the error.

ERRORS

     The getrandom() operation returns the following errors:

     [EAGAIN]           The ‘GRND_NONBLOCK’ flag was set and the random(4) device was not yet
                        seeded.

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

     [EINTR]            The sleep was interrupted by a signal.

     [EINVAL]           An invalid flags was specified.

     [EINVAL]           The requested buflen was larger than IOSIZE_MAX.

SEE ALSO

     arc4random(3), getentropy(3), random(4)

STANDARDS

     getentropy() is non-standard.  It is present in Linux.

HISTORY

     The getrandom() system call first appeared in FreeBSD 12.0.