os-monitor

A very simple monitor for the built-in os, fs modules in Node.js.

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

Installation

To install the latest stable version of os-monitor:

npm install os-monitor

If you are using an old version of Node.js (older than v18.15.x), you might need the legacy version(1.x) of os-monitor; it supports Node.js back to v0.10.x:

npm install os-monitor@legacy

Synopsis

const { Monitor } = require("os-monitor");

const monitor = new 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
              , diskfree: {
                  '/': 100000, // number of free blocks under which event 'diskfree' is triggered
                  '/home': 100000
                }
              , 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', (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', (event) => {
  console.log(event.type, 'Load average is exceptionally high!');
});

// define handler for a too low free memory
monitor.on('freemem', (event) => {
  console.log(event.type, 'Free memory is very low!');
});

// define a throttled handler
monitor.throttle('loadavg5', (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

Delay in milliseconds between each monitor cycle. Default: 3000

freemem

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

uptime

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

diskfree

Object containing free blocks values, for given file system paths, under which event 'diskfree' is triggered. Supported from Node.js v18.15.x and later. (ref.) Default: {}

critical1

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

(A Unix-specific concept, 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.: https://nodejs.org/api/os.html#os_os_loadavg)

critical5

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

critical15

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

silent

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

stream

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

immediate

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

API

.version

The monitor.version property contains the os-monitor version string.

.start( [options] )

Starts the monitor. Accepts an optional options object.

.stop( )

Stops the monitor.

.isRunning( )

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

.config( [options] )

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

.reset( )

Resets monitor config to its default values.

.on( eventType, handler ), .addListener( eventType, handler )

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

.once( eventType, handler )

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.

.throttle( eventType, handler, delay )

Adds a throttled listener. The throttled listener will not be executed more than once every delay milliseconds.

.unthrottle( eventType, handler )

Removes a throttled listener previously added using .throttle(). handler must be the original function.

.when( eventType )

Returns a Promise that resolves with an event object when eventType is triggered.

.destroy( )

Permanently stops and disables the monitor.

.seconds( n ), .minutes( n ), .hours( n ), .days( n )

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) });

.blocks( bytes, blockSize )

Convenience method to get the right amount of file system blocks.

monitor.blocks(100000000, 4096); // -> 24415 blocks

// start by observing file system path `/filesystem`
monitor.start({
  diskfree: {
    '/filesystem': monitor.blocks(100000000, 4096)
  }
});

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
  "diskfree": {
    "/": 25786328,
    "/home": 12786329
  }, // available blocks per file system path, if any config was passed for 'diskfree' event
  "timestamp": 1394766898 // UNIX Timestamp
}

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

Events API docs: nodejs.org/api/events

Using the monitor as a Readable Stream

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
let fs = require('fs'),
    logFile = fs.createWriteStream('/tmp/log.txt', {flags: 'a'});

monitor.pipe(logFile);

Promise

os-monitor supports Promise, async/await: using .when(eventType) returns a Promise.

monitor.when('freemem').then(event => {
    // ...
});

async function callback() {
    let event = await monitor.when('uptime');
    // ...
}

Monitor class

Need concurrent monitor instances? Multiple instances can be created using the Monitor class:

const { Monitor } = require('os-monitor');

let monitor1 = new Monitor();
let monitor2 = new Monitor();
let monitor3 = new Monitor();

License

os-monitor is released under the MIT License.

100% Free: os-monitor will always be free to use in both proprietary and open-source projects.

Attribution is required: You must retain my name and the license information in any distributed code. These items do not have to be user-facing and can remain within the codebase.