两个横杠啊。

$ mysqldump verbose --help | grep flush
  -F, --flush-logs    Flush logs file in server before starting dump. Note that
                      flushed for each database dumped. The exception is when
                      the logs will be flushed only once, corresponding to the
                      and the log flush to happen at the same exact moment you
                      --flush-logs.
  --flush-privileges  Emit a FLUSH PRIVILEGES statement after dumping the mysql