os-monitor

simple OS monitoring for Node.js

os-monitor

A very simple monitor for the built-in os module in Node.js.

Allows you to observe some OS parameters, such as free memory available or load average.

npm install os-monitor

Synopsis

var monitor = require("os-monitor");
 
 
// basic usage 
monitor.start();
 
// more advanced usage with configs. 
monitor.start({ delay: 3000 // interval in ms between monitor cycles 
              , freemem: 1000000000 // freemem under which event 'freemem' is triggered 
              , uptime: 1000000 // number of secs over which event 'uptime' is triggered 
              , critical1: 0.7 // loadavg1 over which event 'loadavg1' is triggered 
              , critical5: 0.7 // loadavg5 over which event 'loadavg5' is triggered 
              , critical15: 0.7 // loadavg15 over which event 'loadavg15' is triggered 
              , silent: false // set true to mute event 'monitor' 
              , stream: false // set true to enable the monitor as a Readable Stream 
              , immediate: false // set true to execute a monitor cycle at start() 
              });
 
 
// define handler that will always fire every cycle 
monitor.on('monitor', function(event) {
  console.log(event.type, ' This event always happens on each monitor cycle!');
});
 
// define handler for a too high 1-minute load average 
monitor.on('loadavg1', function(event) {
  console.log(event.type, ' Load average is exceptionally high!');
});
 
// define handler for a too low free memory 
monitor.on('freemem', function(event) {
  console.log(event.type, 'Free memory is very low!');
});
 
// define a throttled handler, using Underscore.js's throttle function (http://underscorejs.org/#throttle) 
monitor.throttle('loadavg5', function(event) {
 
  // whatever is done here will not happen 
  // more than once every 5 minutes(300000 ms) 
 
}, monitor.minutes(5));
 
 
// change config while monitor is running 
monitor.config({
  freemem: 0.3 // alarm when 30% or less free memory available 
});
 
 
// stop monitor 
monitor.stop();
 
 
// check whether monitor is running or not 
monitor.isRunning(); // -> true / false 
 
 
// use as readable stream 
monitor.start({stream: true}).pipe(process.stdout);
 

config options

Delay in milliseconds between each monitor cycle. Default: 3000

Amount of memory in bytes under which event 'freemem' is triggered. Can also be a percentage of total memory. Default: 0

Number of seconds over which event 'uptime' is triggered. Default: undefined

Value of 1 minute load average over which event 'loadavg1' is triggered. Default: os.cpus().length

(The load average is a measure of system activity, calculated by the operating system and expressed as a fractional number. As a rule of thumb, the load average should ideally be less than the number of logical CPUs in the system. ref.: http://nodejs.org/api/os.html#os_os_loadavg)

Value of 5 minutes load average over which event 'loadavg5' is triggered. Default: os.cpus().length

Value of 15 minutes load average over which event 'loadavg15' is triggered. Default: os.cpus().length

Set true to mute event 'monitor'. Default: false

Set true to enable the monitor as a Readable Stream. Default: false

Set true to execute a monitor cycle at start(). Default: false

methods

Starts the monitor. Accepts an optional options object.

Stops the monitor.

Checks whether the monitor is running or not; returns a boolean.

Accepts an optional options object and updates monitor config. Always returns monitor config options.

Resets monitor config to its default values.

Adds a listener for the specified event type. Supported events are: 'monitor', 'uptime', 'freemem', 'loadavg1', 'loadavg5', 'loadavg15', 'start', 'stop', 'config', 'reset', 'destroy'.

Adds a one-time listener for the specified event type. This listener is invoked only the next time the event is fired, after which it is removed.

Adds a throttled listener, using Underscore.js's throttle function. The throttled listener will not be executed more than once every delay milliseconds.

Permanently stops and disables the monitor.

Convenience methods to get the right amount of milliseconds.

monitor.seconds(10); // -> 10000 ms 
 
monitor.minutes(5); // -> 300000 ms 
 
monitor.hours(1); // -> 3600000 ms 
 
monitor.days(1); // -> 86400000 ms 
 
// start with a delay of 5000 ms 
monitor.start({ delay: monitor.seconds(5) });
 

Event object

There is some useful information in the provided event object:

{
  type: 'monitor', // event type
  loadavg: [ 0.4599609375, 0.53076171875, 0.4990234375 ], // load average values for 1, 5, 15 minutes
  uptime: 1614056, // os uptime in seconds
  freemem: 241262592, // free memory available in bytes
  totalmem: 2147483648, // total memory available in bytes
  timestamp: 1394766898 // UNIX Timestamp
}

All supported events are: 'monitor', 'uptime', 'freemem', 'loadavg1', 'loadavg5', 'loadavg15', 'start', 'stop', 'config', 'reset', 'destroy'. Note that os-monitor is an instance of EventEmitter.

Events API docs: nodejs.org/api/events

os-monitor can also be used as a Readable Stream.

monitor.start({ stream: true });
 
 
// write to STDOUT
monitor.pipe(process.stdout);
 
 
// write to a file
var fs = require('fs'),
    logFile = fs.createWriteStream('/tmp/log.txt', {flags: 'a'});
 
monitor.pipe(logFile);

Need concurrent monitor instances? The monitor class is available from the os-monitor object:

var osm = require('os-monitor');
 
var monitor1 = new osm.Monitor();
var monitor2 = new osm.Monitor();
var monitor3 = new osm.Monitor();

The node os built-in module is also available from the os-monitor object:

var osm = require('os-monitor');
 
var type = osm.os.type();
var cpus = osm.os.cpus();

Documentation for the os module is available here.