[Upcycle It] WiFi Connected Smoke Detector #8: Mosquitto Bites

Road to the finish

I've completed development of main components of the solution (monitor and detector) in previous weeks. The next step was integrating them into a complete system and performing testing. One think I've decided to add is automatic start of all required components after Edison reboot. Linux has pretty good capabilities to accomplish this task, so I didn't expected any  surprises. But I was wrong in my expectations.

I've used a simple instruction  Running Your Node.js App With Systemd to start all components of the system. systemd is responsible to orchestrate boot sequence of Linux services. I've added my monitor and detector as services, which have dependencies on Mosquitto.

Here is my sequence of actions:

1. Created smoke detector service /lib/systemd/system/smoke-detector.service file and specified environment variable for Mosquitto:

[Unit]
Description=SmokeDetectorApp
After=mosquitto.service
Requires=mosquitto.service

[Service]
Environment=MQTT_BROKER_URL=mqtt://192.168.10.114
Type=simple
User=root
TimeoutStartSec=10
ExecStart=/usr/bin/node /home/root/detector.js
Restart=on-failure

[Install]
WantedBy=multi-user.target

2. Created monitor service /lib/systemd/system/home-monitor.service file and specified environment variables for Mosquitto, Slack and Cronitor:

[Unit]
Description=HomeMonotorApp
After=mosquitto.service
Requires=mosquitto.service

[Service]
Environment=MQTT_BROKER_URL=mqtt://192.168.10.114
Environment=SLACK_API_TOKEN=<my Slack API token>
Environment=SLACK_CHANNEL=<my Slack channel for Alarms>
Environment=CRONITOR_MONITOR=<my Cronitor alarm id>
Environment=CRONITOR_AUTH_TOKEN=<my cronitor API token>
Type=simple
User=root
TimeoutStartSec=10
ExecStart=/usr/bin/node /home/root/home.js
Restart=on-failure

[Install]
WantedBy=multi-user.target

3. Reload systemctl

sudo systemctl daemon-reload

4. Start new services

sudo systemctl start home-monitor
sudo systemctl start smoke-detector

5. Check if there is no issues by looking at failed services

systemctl --failed

and reviewing the system journal entries:

journalctl --since=today

As well status of services can be checked by running:

sudo systemctl status  home-monitor
sudo systemctl status  smoke-detector

6. Make it permanent

sudo systemctl enable home-monitor
sudo systemctl enable smoke-detector

7. Reboot

init 6

and repeat step 5 after startup.

Bump on the road or Mosquitto bites

We have an unusually cold spring in Canada this year. I haven't seen any mosquitoes yet flying outside. But I've got bitten by Mosquitto MQTT broker. Here is the story. I've configured Mosquitto to retain messages. After persistence was configured in /etc/mosquitto/mosquitto.conf the broker created database in /var/lib/mosquitto/mosquitto.db to store messages. During my tests I rebooted the Edison board several times. After one of these reboots the broker fails to start:

root@gate1:~# sudo systemctl status  mosquitto
● mosquitto.service - Mosquitto - lightweight server implementation of the MQTT and MQTT-SN protocols
   Loaded: loaded (/lib/systemd/system/mosquitto.service; enabled)
   Active: failed (Result: start-limit) since Sat 2017-05-13 15:36:53 EDT; 52s ago
  Process: 374 ExecStart=/usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf (code=exited, status=1/FAILURE)
  Process: 372 ExecStartPre=/bin/rm -f /var/run/mosquitto.pid (code=exited, status=0/SUCCESS)
 Main PID: 374 (code=exited, status=1/FAILURE)

Then I've tried to start it from command line:

root@gate1:~# /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf
1494704860: Warning: Mosquitto should not be run as root/administrator.
1494704860: Error: No such file or directory.
1494704860: Error: Couldn't open database.

So, something should be wrong with Mosquitto database.

root@gate1:~# ls -la /var/lib/mosquitto/
total 8
drwxr-xr-x  2 root root 4096 May 13 15:31 .
drwxr-xr-x 14 root root 4096 Apr 10 23:04 ..
-rw-r--r--  1 root root 0 May 13 15:31 mosquitto.db

Well, it is empty and the broker can't recover it. I've deleted the empty file and the broker was able to start this time without errors.

Source control

The code is now uploaded to my github repository. If you encountered any issues or would like to request new features you can do it there as well.