The Monitoring module is a Rule Engine that allows writing simple scriplet to implement basic logic, based on a set of events (called triggers), executing some function (called actions).

The general idea of the Monitoring Script Engine is to instanciate your triggers and actions and then connect them. The rule language is actually based on Lua which make easy to write clean and simple rules to implement your logic. Scriptlets can be loaded and unloaded dynamically in the system (See monitoring module APIs).

The Monitoring Script Engine comes with a set of predefined triggers and actions that can be used in a scriptlet.

Predefined triggers



Activated when the agent is started, usually when the device boots (depends on how it is ported).



Activated before a connection with the Device Management Server is done.

Note this trigger is temporarily unavailable (need to work on the server connector module of the agent)



Activated on a timer:



Activated on a date. This date is specified with a cron entry (see timer.cron documetnation for format).

Ex: With the compatible Unix CRON syntax, "22 7 * * *" means every day at 7:22 am



Activated when one of the variable from the list changes.

... is a variable number of variable to monitor, named as string: ex "system.batterylevel", "user.somevar", etc.

The first argument can also be a table containing all the variables, in that case the remaining args are ignored.

Note the action functions will be given a table containing the changed variables and their value as first argument


onhold(timeout, ...)

Activated when none of the listed variables change for the timeout amount of time.

Note the action functions will be given a table containing the variables and the value that caused the last rearm of the holding timer, as first argument


onthreshold(threshold, var, edge)

Activated when a value traverse a threshold (previous and new value are opposite side of the threshold value) when edge is specified it can be one of "up", "down", "both" meaning only triggering on rising edge or falling edge, or on both.


ondeadband(deadband, var)

Activated when a value goes outside the deadband range: activated if abs(newval-oldval) >= deadband.

oldval is updated when the trigger is activated.

Predefined actions

Actions are regular Lua functions. Most of the framework API can be used for that purpose.

For typical actions, see the Racon Lua library.

Filtering and connecting rules

The system provides two additional functions to write the rule scriplets.


connect(trigger, action)

Connects a trigger to an action. The action will be executed each time the trigger is activated.

Optionally some triggers will pass some parameters to the action function. See the trigger documentation for more details.


filter(test, trigger)

Filter a trigger given a test function.

In filter returns a new trigger that has the original trigger behavior filtered by the test function.


           function() return not system.externalpower end,
    function() print("Battery Level Changed") end)

will only print the battery level when it changes and the power cord is unplugued.

Monitoring variables

Each monitoring script has its own execution environment. It means that a global lua variable will not be visible from another monitoring script.

Scriptlets can register events on device tree variable changes. The whole device tree is accessible, provided the scriptlet has the correct permissions.

The device tree structure depends heavily on what Tree Manager handlers (extensions) has been ported on the device.

The following list is a guideline to name variables in an homogenous way across devices. Some of there variables might not be available depending on your hardware and how Mihini was ported on the device.


Variable name Variable Type Variable description Available on
cellurar.rssi integer Cellular RSSI level On any device that support the standard AT+CSQ AT command
cellular.ber integer Cellular BER level On any device that support the standard AT+CSQ AT command
cellular.imei string Cellular IMEI On any device that support the standard AT+CGSN AT command
cellular.imsi string SIM IMSI number On any device that support the standard AT+CIMI AT command


Variable name Variable Type Variable description Available on
batterylevel integer Level of charge of the device battery
externalpower boolean true if the device is powered by an external source

Memory / CPU

Variable name Variable Type Variable description Available on
luaramusage integer Quantity of memory used by the Lua VM (the one running the agent)
The value is the one returned by collectgarbage("count") preceded by a collectgarbage("collect") in order to provided consistent numbers. The direct consequence is that reading this variable has a non null CPU cost. Use sparingly.
All (included in standard lua)
totalramavailable integer Total quantity of RAM available on the system Linux
totalramused integer Total quantity of RAM used on the system Linux
cpuload integer Average CPU load Linux
totalflashavailable integer Total quantity of flash available on the system
totalflashused integer Total quantity of flash used on the system


Variable name Variable Type Variable description Available on
netman.BEARERNAME.connected boolean connection state of the bearer
netman.BEARERNAME.ipaddr string ip address of the bearer
netman.BEARERNAME.hwaddr string MAC address of the bearer Ethernet bearer
netman.BEARERNAME.netmask string netmask address of the bearer string gateway address of the bearer
netman.BEARERNAME.nameserver1 string dns address #1 (there can be several dns address, usually 2)
netman.BEARERNAME.mountdate number timestamp of the last successful mount
netman.BEARERNAME.mountretries number number of retries used for the last successful mount
netman.BEARERNAME.RX number number of bytes received by this bearer Linux only
netman.BEARERNAME.TX number number of bytes transmitted by this bearer Linux only
netman.defaultbearer string Default (=selected) bearer: bearer used as default route, variable value is the BEARERNAME

Monitoring Engine API

The Monitoring Engine can install and load scripts dynamically.

Load scriptlets

-- Load a monitoring script in memory.
-- name is a string name
-- script can be either
--              a string containing a monitoring script
--              a table string buffer (list of chunk of string)
--              or an actual Lua function containing the script
load(name, script)

-- Unload (and stop) a monitoring script from memory.
-- name is a string name, given at loading time (see load() )

Install scriptlets

-- Install a monitoring script from a file. Installing a script with an already used name will cause the
-- initial script to be unloaded and uninstalled (replaced by this script)
--      name is the name given to the script
--      filename is the path of the file to install
--      enable is a boolean. true means that the script will enabled (started)
install(name, filename, enable)

-- Uninstall a monitoring script.
-- This function automatically stop the given script if it was enabled (running).
--      name is the name given at installation time.

Manage scriptlets

-- Set the enable flag on an already installed script.
-- Enabling a disabled script will cause a loading, and similarly, disabling an enabled
-- script will cause an unloading.
--      name is the name of the script to configure
--      set is a boolean: true will enable the script, false will disable the script
enable(name, set)

-- List installed or loaded scripts.
--      type: if type is set to "installed", list the installed scripts
--            if type is set to "loaded", list the loaded scripts

Scriptlets Examples

Flip a GPIO every 10 seconds

    function() system.gpio[4] = not system.gpio[4] end)

Activate a GPIO when battery is low

    onthreshold(10, "system.batterylevel", "down"),
    function() system.gpio[4] = true end)

Send an alarm on high temperature

local t = onthreshold(55, "system.temperature", "up")
local a = function()
    pushdata("alarm.temperature", {value = system.temperature, timestamp = time()})
connect(t, a)
           function() return not system.externalpower end,
    function() print("Battery Level Changed") end)