Mosquitto MQTT on TinyCore Linux

Build an Extension

There is no prebuilt extension for Mosquitto which means that have to build the program from source and create a custom extension for TinyCore Linux.

First, download the source and unpack:

$ wget http://mosquitto.org/files/source/mosquitto-1.4.10.tar.gz
$ tar -xzf mosquitto-1.4.10.tar.gz

Next, install build dependencies.

$ tce-load -w make
$ tce-load -w gcc
$ tce-load -w compiletc
$ tce-load -w openssl-dev
$ tce-load -w squashfs-tools

$ tce-load -i make
$ tce-load -i gcc
$ tce-load -i compiletc
$ tce-load -i openssl-dev
$ tce-load -i squashfs-tools

./Makefile
./lib/Makefile
./lib/cpp/Makefile
./client/Makefile
./src/Makefile

$ cd mosquitto-1.4.10/
$ make
$ make WITH_SRV=no WITH_UUID=no

$ sudo make install WITH_DOCS=no DESTDIR=/tmp/mosquitto

$ mksquashfs /tmp/mosquitto/ /tmp/mosquitto.tcz
$ rm -rf /tmp/mosquitto
$ mv /tmp/mosquitto.tcz /etc/sysconfig/tcedir/optional/

$ tce-load -i mosquitto

$ echo mosquitto.tcz >> /etc/sysconfig/tcedir/onboot.lst

Create User

To run Mosquitto with a dedicated user, create that user:

$ sudo adduser -S mosquitto

And edit configuration accordingly.

Configuration

The config file goes into /usr/local/etc/mosquitto.conf. This is not the default location, so we need to use the --config-file option when starting Mosquitto to tell it where to look for configuration.

Of course, the config file should be included in the list of files to be backed up and restored on boot. Include it in /opt/.filetool.lst:

usr/local/etc/mosquitto.conf

log_dest file /var/log/mosquitto.log

persistence true
persistence_location /var/lib/mosquitto/
persistence_file mosquitto.db
autosave_interval 1800

var/lib/mosquitto

pid_file /var/run/mosquitto.pid

Start on boot

To start the service on boot, include this in /opt/bootlocal.sh:

# start Mosquitto in background
touch /var/log/mosquitto.log
chown mosquitto:staff /var/log/mosquitto.log
mkdir -p /var/lib/mosquitto
chown mosquitto:staff /var/lib/mosquitto
mosquitto --daemon --config-file /usr/local/etc/mosquitto.conf

This will start Mosquitto as root unless the configuration file defines the user to run as:

user mosquitto

Which is recommended.

Shutdown

To shutdown gracefully, include this in /opt/shutdown.sh:

# stop mosquitto
mosquitto_pid=$(cat /var/run/mosquitto.pid)
if [ -n "$mosquitto_pid" ]; then
    kill "$pid"
fi

Monitoring with monit

To use monit [6] to monitor Mosquitto, add these checks to monitrc (or in a separate file in monit.d/):

check process mosquitto pidfile /var/run/mosquitto.pid
    group mqtt
    if failed uid mosquitto then alert

check program mqtt-connect
with path "/usr/local/bin/mosquitto_sub --quiet -C 1 --id monit --topic $SYS/broker/version"
    group mqtt
    if status != 0 then alert

In order to check if the broker is running, connect to it and retrieve one message. We request a message from the $SYS hierarchy and pick one that is static so that we can be sure that it exists. The $SYS hierarchy is described in the Mosquitto docs [7].

mosquitto_sub comes with the Mosquitto installation an we can use it like this:

$ mosquitto_sub --quiet -C 1 --id monit --topic \$SYS/broker/version

This should be sufficient, i.e. exit with "0" if the connection was possible. The -C 1 options is necessary to exit the program after the first message. Note that you need to escape the "$" for the command line but not in monitrc.