MQTT broker setup (Mosquitto) in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Mosquitto Broker Default Port

What is the default port number on which the Mosquitto MQTT broker listens for client connections?

A 8080

B 8883

C 80

D 1883

💡 Hint

Think about the standard port used for unencrypted MQTT connections.

Mosquitto listens on port 1883 by default for MQTT clients without encryption.

❓ Predict Output

intermediate

Mosquitto Service Status Command

Which command correctly checks the status of the Mosquitto service on a Raspberry Pi running systemd?

A sudo systemctl status mosquitto

B sudo service mosquitto check

C sudo mosquitto --status

D sudo systemctl mosquitto status

💡 Hint

Use the systemctl command with the correct syntax to check service status.

The correct command to check Mosquitto service status is 'sudo systemctl status mosquitto'.

🔧 Debug

advanced

Mosquitto Configuration File Syntax Error

Given this snippet from a Mosquitto configuration file, what error will Mosquitto report when starting? listener 1883 allow_anonymous true password_file /etc/mosquitto/passwd Options:

Raspberry Pi

listener 1883
allow_anonymous true
password_file /etc/mosquitto/passwd

A Error: 'password_file' path not found

B Error: Invalid listener option 'password_file'

C No error, Mosquitto starts normally

D Error: 'listener' directive requires a protocol

💡 Hint

Check which configuration options are valid within a listener context.

'password_file' is a global configuration option and cannot be placed within a listener context (i.e., after a 'listener' directive without ending the block).

🧠 Conceptual

advanced

Mosquitto Authentication Setup

Which of the following steps is necessary to enable username/password authentication in Mosquitto on Raspberry Pi?

A Enable anonymous access and disable password file

B Install a separate authentication plugin from the Raspberry Pi repository

C Create a password file using 'mosquitto_passwd' and reference it in the config

D Change the default port to 8883

💡 Hint

Think about how Mosquitto manages user credentials by default.

Mosquitto uses a password file created by 'mosquitto_passwd' to authenticate users.

❓ Predict Output

expert

Mosquitto Broker Log Output

After starting Mosquitto with the command 'mosquitto -v' on Raspberry Pi, which output line indicates the broker is ready and listening on port 1883?

A

"1623456789: mosquitto version 2.0.15 starting"
"1623456789: Opening ipv4 listen socket on port 1883."

B "1623456789: Error: port 1883 already in use"

C "1623456789: mosquitto version 2.0.15 shutting down"

D "1623456789: Client connected from 192.168.1.10"

💡 Hint

Look for messages about opening sockets and starting version.

The log line showing 'Opening ipv4 listen socket on port 1883' means the broker is ready to accept connections.