介绍

我在亚马逊主机上安装了mosquitto作为mqtt服务器，在树莓派上找了一个python客户端库paho，安装后找了一个例程：
https://github.com/eclipse/paho.mqtt.python#constructor-reinitialise
nano test.py:

import paho.mqtt.client as mqtt

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))

    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("$SYS/#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("iot.eclipse.org", 1883, 60)

# Blocking call that processes network traffic, dispatches callbacks and
# handles reconnecting.
# Other loop*() functions are available that give a threaded interface and a
# manual interface.
client.loop_forever()

chmod +x test.py
python ./test.py

运行正常，但当我将服务器地址改为我在aws上的地址时，服务器报

Invalid protocol "MQTT"...

解决方案

经多方查证，问题的根源处在mosquitto，我服务器（ubuntu14.04）上的版本太旧，在mtqq v3.1和v3.11版本兼容性上出了问题，那解决之道就是更新mosquitto版本了：

wget http://repo.mosquitto.org/debian/mosquitto-repo.gpg.key
sudo apt-key add mosquitto-repo.gpg.key
cd /etc/apt/sources.list.d/
sudo wget http://repo.mosquitto.org/debian/mosquitto-jessie.list
sudo apt-get update
sudo apt-get install mosquitto

安装新版本后问题解决。