树莓派3与Node-RED MQTT连接失败求助：无法连接mqtt://localhost:1883

Hey there, let's work through this MQTT connection issue you're facing. Those repeated failures to connect to mqtt://localhost:1883 typically stem from a handful of common issues—here's a step-by-step guide to diagnose and fix them:

1. Verify the MQTT Broker is Installed and Running #

Most Raspberry Pi setups use Mosquitto as the default MQTT broker. First, check if it's active:

sudo systemctl status mosquitto

• If the output shows it's not running, start it with:

  sudo systemctl start mosquitto
  

• To make sure it launches on boot, enable the service:

  sudo systemctl enable mosquitto
  

• If Mosquitto isn't installed at all, install it first:

  sudo apt update && sudo apt install mosquitto mosquitto-clients
  

2. Check if Port 1883 is Being Listened On #

Confirm the broker is actually listening on the default MQTT port. Run either of these commands:

netstat -tulpn | grep 1883
# Or use ss if netstat isn't installed
ss -tulpn | grep 1883

You should see an entry for mosquitto listening on 127.0.0.1:1883 (or 0.0.0.0:1883 for all interfaces). If no entry appears, check the broker's configuration file (/etc/mosquitto/mosquitto.conf) to ensure it's not set to listen on a different port or disabled.

3. Test Local MQTT Connectivity Directly #

Rule out Node-RED as the issue by testing the broker with native MQTT clients:

1. Open one terminal window and subscribe to a test topic:

   mosquitto_sub -h localhost -t test/topic
   

2. Open a second terminal and publish a message to the same topic:

   mosquitto_pub -h localhost -t test/topic -m "Hello from Mosquitto"
   

If the first terminal receives the message, your broker is working correctly—focus your troubleshooting on Node-RED's configuration.

4. Double-Check Node-RED MQTT Node Configuration #

• Open your Node-RED editor, navigate to the failing MQTT broker node (165e8c2d.4cb0d4).
• Confirm the Server field is set to localhost or 127.0.0.1 (avoid using hostnames that might resolve incorrectly).
• If your broker requires authentication, ensure the Username and Password fields match what's configured in Mosquitto. If you haven't set up auth yet, temporarily enable anonymous access in /etc/mosquitto/mosquitto.conf (comment out allow_anonymous false and any password_file lines) and restart the broker to test.

5. Check for Firewall or Network Restrictions #

While local connections usually bypass firewalls, if you have ufw enabled on your Pi, verify it's not blocking port 1883:

sudo ufw status

If needed, allow local MQTT traffic or temporarily disable the firewall to test:

sudo ufw disable

If connecting works after disabling, re-enable the firewall and add a rule for port 1883:

sudo ufw enable
sudo ufw allow 1883/tcp

6. View Detailed Node-RED Logs #

Get more context from Node-RED's real-time logs to pinpoint the exact failure reason:

journalctl -u nodered.service -f

This will show live logs as Node-RED runs—look for additional error details like authentication failures or connection timeouts that might not be in the truncated logs you shared.

Start with the first couple of steps, as a stopped or missing broker is the most frequent cause of this issue. Let me know if any of these steps help you resolve the problem!

内容的提问来源于stack exchange，提问作者DOE