MqttDasherService

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title: MqttDasherService
---

Create an mqtt-dasher service. (Debian/Ubuntu distros).

mqtt-dasher
:   <https://github.com/stjohnjohnson/mqtt-dasher>

Limits permissions for promiscuous net socket access via libpcap.

This assumes `npm install` without the global flag so uses `/opt/node_modules` instead of `/usr/lib`.

# Install

# install nodejs from debsource
    curl -sL https://deb.nodesource.com/setup_5.x | sudo -E bash -
    sudo apt-get install -y nodejs
    
    # install mqtt-dasher and libpcap dependency
    sudo apt-get install libpcap-dev
    sudo npm install mqtt-dasher
    
    # add user to run the service, and group to limit access to setcap files
    sudo useradd mqtt-dasher -d /opt/node_modules/mqtt-dasher -U
    
    # make a copy of nodejs to set privileged net capabilities on
    sudo cp `which nodejs` /opt/node_modules/mqtt-dasher/nodejs.setcap
    
    # set user and group for mqtt-dasher first
    sudo chgrp mqtt-dasher /opt/node_modules/mqtt-dasher/nodejs.setcap
    sudo chmod 750 /opt/node_modules/mqtt-dasher/nodejs.setcap
    
    # allow raw sockets and net admin for promiscuous mode
    sudo setcap 'CAP\_NET\_RAW+eip CAP\_NET\_ADMIN+eip' /opt/node_modules/mqtt-dasher/nodejs.setcap

## Create the Service

`/etc/systemd/system/mqtt-dasher.service`

[Unit]
    Description=mqtt-dasher service
    
    [Service]
    ExecStart=/opt/node_modules/mqtt-dasher/nodejs.setcap /opt/node_modules/mqtt-dasher/server.js
    # WorkingDirectory=/opt/node_modules/mqtt-dasher   # Required on some systems
    Restart=always
    RestartSec=10             # Restart service after 10 seconds if node service crashes
    StandardOutput=syslog     # Output to syslog
    StandardError=syslog      # Output to syslog
    SyslogIdentifier=mqtt-dasher
    User=mqtt-dasher
    Group=mqtt-dasher
    Environment=CONFIG_DIR=/etc/mqtt-dasher NODE_ENV=production
    
    [Install]
    WantedBy=multi-user.target

# Configure and start

sudo mkdir /etc/mqtt-dasher

[[$[Get Code]]][2]

`/etc/mqtt-dasher/config.yml`

mqtt:
      host: localhost
      ## Preface for the topics $PREFACE/$TOPIC
      ## (not in mqtt-dasher 0.1.0)
      #preface: ha/dash
    
    buttons:
      ab:cd:ef:12:34:56: ha/dash/listerine

sudo systemctl enable mqtt-dasher
    sudo systemctl start mqtt-dasher

# Home Assistant Switch

An mqtt switch which:

*   turns on when the dash button is activated 
*   turns off when the dash button deactivates 
*   can be activated and deactivated from HA

switch:
    - name: Listerine
      platform: mqtt
      command_topic: ha/dash/listerine
      state_topic: ha/dash/listerine
      payload_on: 'active'
      payload_off: 'inactive'
      retain: false

The switch isn't intended to be used in the HA UI, it should be mapped to a script instead.

# To Do

Compile mqtt-dasher with [nexe][5] so that `nodejs.setcap` can't be so easily abused.

[1]: MqttDasherService?action=sourceblock&num=1
 [2]: MqttDasherService?action=sourceblock&num=2
 [3]: MqttDasherService?action=sourceblock&num=3
 [4]: MqttDasherService?action=sourceblock&num=4
 [5]: https://github.com/nexe/nexe

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