RAND_file_name() generates a default path for the random seed file. buf points to a buffer of size num in which to store the filename. The seed file is $RANDFILE if that environment variable is set, $HOME /.rnd otherwise. If $HOME is not set either, or num is too small for the path name, an error occurs.RAND_load_file() reads a number of bytes from file filename and adds them to the PRNG. If max_bytes is non-negative, up to to max_bytes are read; starting with OpenSSL 0.9.5, if max_bytes is -1, the complete file is read.
RAND_write_file() writes a number of random bytes (currently 1024) to file filename which can be used to initialize the PRNG by calling RAND_load_file() in a later session.