MQTT with Mosquitto

Using Mosquitto as a Message Broker

Updated: 03 September 2023

MQTT makes use of a publish/subscribe model in which a client will either publish messages to a topic or subscribe to messages on the topic

Help

We can run the following to get the mosquitto help menus

General

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> mosquitto --help
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mosquitto version 1.5.4
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mosquitto is an MQTT v3.1.1 broker.
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Usage: mosquitto [-c config_file] [-d] [-h] [-p port]
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 -c : specify the broker config file.
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 -d : put the broker into the background after starting.
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 -h : display this help.
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 -p : start the broker listening on the specified port.
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      Not recommended in conjunction with the -c option.
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 -v : verbose mode - enable all logging types. This overrides
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      any logging options given in the config file.
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See http://mosquitto.org/ for more information.

Publisher

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> mosquitto_pub --help
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mosquitto_pub is a simple mqtt client that will publish a message on a single topic and exit.
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mosquitto_pub version 1.5.4 running on libmosquitto 1.5.4.
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Usage: mosquitto_pub {[-h host] [-p port] [-u username [-P password]] -t topic | -L URL}
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                     {-f file | -l | -n | -m message}
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                     [-c] [-k keepalive] [-q qos] [-r]
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                     [-A bind_address]
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                     [-i id] [-I id_prefix]
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                     [-d] [--quiet]
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                     [-M max_inflight]
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                     [-u username [-P password]]
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                     [--will-topic [--will-payload payload] [--will-qos qos] [--will-retain]]
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                     [{--cafile file | --capath dir} [--cert file] [--key file]
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                      [--ciphers ciphers] [--insecure]]
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                     [--psk hex-key --psk-identity identity [--ciphers ciphers]]
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                     [--proxy socks-url]
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       mosquitto_pub --help
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...

Subscriber

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> mosquitto_sub --help
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mosquitto_sub is a simple mqtt client that will subscribe to a set of topics and print all messages it receives.
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mosquitto_sub version 1.5.4 running on libmosquitto 1.5.4.
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Usage: mosquitto_sub {[-h host] [-p port] [-u username [-P password]] -t topic | -L URL [-t topic]}
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                     [-c] [-k keepalive] [-q qos]
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                     [-C msg_count] [-R] [--retained-only] [-T filter_out] [-U topic ...]
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                     [-F format]
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                     [-A bind_address]
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                     [-i id] [-I id_prefix]
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                     [-d] [-N] [--quiet] [-v]
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                     [--will-topic [--will-payload payload] [--will-qos qos] [--will-retain]]
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                     [{--cafile file | --capath dir} [--cert file] [--key file]
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                      [--ciphers ciphers] [--insecure]]
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                     [--psk hex-key --psk-identity identity [--ciphers ciphers]]
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                     [--proxy socks-url]
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       mosquitto_sub --help
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...

Starting a Server

We can start an MQTT Broker Server with mosquitto in verbose mode as follows

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mosquitto -v

This will allow us to publish and subscribe message

We can subscribe to a topic with the following

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mosquitto_sub -t "hello" -v

Publish to a Topic

We can publish messages to a topic with the following

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mosquitto_pub -t "hello" -m "Hello World!"