mosquitto_sub

subscribes to MQTT topics and prints received messages

TLDR

Subscribe to topic

$ mosquitto_sub -t [sensors/temperature]

Subscribe to all topics

$ mosquitto_sub -t '#'

Subscribe with wildcard

$ mosquitto_sub -t '[sensors/+/temperature]'

Connect to remote broker

$ mosquitto_sub -h [broker.example.com] -t [topic]

Subscribe with authentication

$ mosquitto_sub -h [broker] -u [username] -P [password] -t [topic]

Subscribe with TLS

$ mosquitto_sub -h [broker] --cafile [ca.crt] -t [topic]

Show verbose output

$ mosquitto_sub -v -t '[sensors/#]'

Read single message and exit

$ mosquitto_sub -t [topic] -C 1

SYNOPSIS

mosquitto_sub [-h host] [-p port] [-t topic] [-u user] [-P pass] [options]

mosquitto_sub subscribes to MQTT topics and prints received messages. MQTT is a lightweight publish/subscribe messaging protocol for IoT and telemetry.Topics use hierarchical naming with / separators. Wildcards expand subscriptions: + matches one level, # matches all remaining levels. For example, sensors/+/temperature matches any sensor's temperature.Quality of Service levels control delivery guarantees: QoS 0 is fire-and-forget, QoS 1 ensures at-least-once delivery, QoS 2 guarantees exactly-once delivery.Retained messages are stored by the broker and sent immediately on subscription. This provides last-known values to new subscribers.TLS encryption protects communication. Client certificates enable mutual authentication. The broker must be configured to accept TLS connections.

PARAMETERS

-t TOPIC

Topic to subscribe to (can repeat).

-h HOST

Broker hostname.

-p PORT

Broker port (default 1883).

-u USER

Username.

-P PASSWORD

Password.

-i ID

Client ID.

-v

Verbose (print topic with message).

-C COUNT

Exit after receiving count messages.

-q QOS

Quality of service (0, 1, 2).

--cafile FILE

CA certificate for TLS.

--cert FILE

Client certificate.

--key FILE

Client private key.

-F FORMAT

Output format string.

-N

Don't append newline to messages.

--retained-only

Only show retained messages.

INSTALL

sudo apt install mosquitto-clients

sudo apk add mosquitto-clients

sudo zypper install mosquitto-clients

CAVEATS

Subscribing to # on busy brokers produces high volume. QoS 2 has significant overhead. Passwords on command line visible in process list.

HISTORY

mosquitto_sub is part of the Eclipse Mosquitto project, an MQTT broker and client suite. Mosquitto was created by Roger Light starting around 2009 and joined the Eclipse Foundation in 2014.