GETRANDOM(2)              FreeBSD System Calls Manual             GETRANDOM(2)

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.

     `GRND_INSECURE'  This flag is treated as an alternative name for
                      GRND_NONBLOCK.  It is provided solely for API
                      compatibility with Linux.

     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' (or `GRND_INSECURE') 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
     getrandom() is non-standard.  It is present in Linux.

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

CAVEATS
     Unlike Linux, the GRND_INSECURE flag on FreeBSD does not produce any
     output before the random(4) device is seeded.

FreeBSD 13.1-RELEASE-p6        January 12, 2020        FreeBSD 13.1-RELEASE-p6