docs: def _check_tcpdump():
      """
      Return True if the tcpdump command can be started
      """
      with open(os.devnull, 'wb') as devnull:
          try:
              proc = subprocess.Popen([conf.prog.tcpdump, "--version"],
                                      stdout=devnull, stderr=subprocess.STDOUT)
          except OSError:
              return False
  
      if OPENBSD:
          # 'tcpdump --version' returns 1 on OpenBSD 6.4
          return proc.wait() == 1
      else:
          return proc.wait() == 0