mosquitto_sub (1)

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NAME

mosquitto_sub - an mqtt version 3.1 client for subscribing to topics

SYNOPSIS

mosquitto_sub [-c] [-d] [-h hostname] [-i client_id] [-I client id prefix] [-k keepalive time] [-p port number] [-q message QoS] [--quiet] [-v] [ -u username [-P password] ] [ --will-topic topic [--will-payload payload] [--will-qos qos] [--will-retain] ] -t message topic ...

DESCRIPTION

mosquitto_sub is a simple mqtt version 3.1 client that will subscribe to a topic and print the messages that it receives.

OPTIONS

-c, --disable-clean-session

Disable the 'clean session' flag. This means that all of the subscriptions for the client will be maintained after it disconnects, along with subsequent QoS 1 and QoS 2 messages that arrive. When the client reconnects, it will receive all of the queued messages.

If using this option, it is recommended that the client id is set manually with --id

-d, --debug

Enable debug messages.

-h, --host

Specify the host to connect to. Defaults to localhost.

-i, --id

The id to use for this client. If not given, defaults to mosquitto_sub_ appended with the process id of the client. Cannot be used at the same time as the --id-prefix argument.

-I, --id-prefix

Provide a prefix that the client id will be built from by appending the process id of the client. This is useful where the broker is using the clientid_prefixes option. Cannot be used at the same time as the --id argument.

-k, --keepalive

The number of seconds between sending PING commands to the broker for the purposes of informing it we are still connected and functioning. Defaults to 60 seconds.

-p, --port

Connect to the port specified instead of the default 1883.

-P, --pw

Provide a password to be used for authenticating with the broker. Using this argument without also specifying a username is invalid. This requires a broker that supports MQTT v3.1. See also the --username option.

-q, --qos

Specify the quality of service desired for the incoming messages, from 0, 1 and 2. Defaults to 0. See mqtt(7) for more information on QoS.

The QoS is identical for all topics subscribed to in a single instance of mosquitto_sub.

--quiet

If this argument is given, no runtime errors will be printed. This excludes any error messages given in case of invalid user input (e.g. using --port without a port).

-t, --topic

The mqtt topic to subscribe to. See mqtt(7) for more information on mqtt topics.

This option may be repeated to subscribe to multiple topics.

-u, --username

Provide a username to be used for authenticating with the broker. This requires a broker that supports MQTT v3.1. See also the --pw argument.

-v, --verbose

Print received messages verbosely. With this argument, messages will be printed as "topic payload". When this argument is not given, the messages are printed as "payload".

--will-payload

Specify a message that will be stored by the broker and sent out if this client disconnects unexpectedly. This must be used in conjunction with --will-topic.

--will-qos

The QoS to use for the Will. Defaults to 0. This must be used in conjunction with --will-topic.

--will-retain

If given, if the client disconnects unexpectedly the message sent out will be treated as a retained message. This must be used in conjunction with --will-topic.

--will-topic

The topic on which to send a Will, in the event that the client disconnects unexpectedly.

WILLS

mosquitto_sub can register a message with the broker that will be sent out if it disconnects unexpectedly. See mqtt(7) for more information.

The minimum requirement for this is to use --will-topic to specify which topic the will should be sent out on. This will result in a non-retained, zero length message with QoS 0.

Use the --will-retain, --will-payload and --will-qos arguments to modify the other will parameters.

EXAMPLES

Note that these really are examples - the subscriptions will work if you run them as shown, but there must be something publishing messages on those topics for you to receive anything.

Subscribe to temperature information on localhost with QoS 1:

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mosquitto_sub -t sensors/temperature -q 1

Subscribe to hard drive temperature updates on multiple machines/hard drives. This expects each machine to be publishing its hard drive temperature to sensors/machines/HOSTNAME/temperature/HD_NAME.

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mosquitto_sub -t sensors/machines/+/temperature/+

Subscribe to all broker status messages:

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mosquitto_sub -v -t \$SYS/#

BUGS

mosquitto_sub bug information can be found at http://launchpad.net/mosquitto

SEE ALSO

mqtt(7) mosquitto_pub(1) mosquitto(8) libmosquitto(3)

AUTHOR

Roger Light <roger@atchoo.org>

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