Syslog logging for node.js
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Brain-free syslog** logging for node.js.

Ain is written with full compatibility with node.js console module. It implements all console functions and formatting. Also ain supports UTF-8 (tested on Debian Testing/Sid).

Ain can send messages by UDP to or to the a unix socket; /dev/log on Linux and /var/run/syslog on Mac OS X. The unix sockets only work for the 0.4.x versions of node.js, unix_dgram sockets support has been removed from > 0.5.x.

*In the Phoenician alphabet letter "ain" indicates eye.

**All examples tested under Ubuntu rsyslog. On other operating systems and logging daemons settings and paths may differ.


You can install ain as usual - by copy the "ain" directory in your ~/.node_modules or via npm

npm install ain2


Usage of ain is very similar to the node.js console. The following example demonstrates the replacement of the console:

var SysLogger = require('ain2');
var console = new SysLogger();

console.log('notice: %d',;'info');

After launch in /var/log/user you can see the following:

Dec  5 06:45:26 localhost ex.js[6041]: notice: 1291513526013
Dec  5 06:45:26 localhost ex.js[6041]: info
Dec  5 06:45:26 localhost ex.js[6041]: error

Singleton logger

If you want to have a singleton that points to the same object whenever you do a require, use the following:


If you use this, please be beware of this:

require('ain2').getInstance() ===  require('ain2').getInstance();
=> true

As opposed to:

var SysLogger = require('ain2');
new SysLogger() === new SysLogger();
=> false

Changing destinations

By default ain sets following destinations:

  • TAG - __filename
  • Facility - user (1)
  • HOSTNAME - localhost
  • PORT - 514
  • Transport - UDP or Unix socket

You can change them by passing in the params to the constructor or by using the set function. The set function is chainable.

var SysLogger = require('ain2');
var logger = new SysLogger({tag: 'node-test-app', facility: 'daemon', hostname: 'devhost', port: 3000});

logger.warn('some warning');

... and in /var/log/daemon.log:

Dec  5 07:08:58 devhost node-test-app[10045]: some warning

The set function takes one argument, a configuration object which can contain the following keys:

  • tag - defaults to __filename
  • facility - defaults to user
  • hostname - defaults to require('os').hostname()
  • port - defaults to 514
  • transport - defaults to 'UDP', can also be 'file'
  • messageComposer - a custom function to compose syslog messages

All of these are optional. If you provide a hostname transport is automatically set to UDP

tag and hostname arguments is just RFC 3164 TAG and HOSTNAME of your messages.

facility is little more than just name. Refer to Section 4.1.1 of RFC 3164 it can be:

##  String  Description
 0  kern    kernel messages
 1  user    user-level messages
 2  mail    mail system
 3  daemon  system daemons
 4  auth    security/authorization messages
 5  syslog  messages generated internally by syslog daemon
 6  lpr     line printer subsystem
 7  news    network news subsystem
 8  uucp    UUCP subsystem
16  local0  local use 0
17  local1  local use 1
18  local2  local use 2
19  local3  local use 3
20  local4  local use 4
21  local5  local use 5
22  local6  local use 6
23  local7  local use 7

You can set the facility by String or Number:

logger.set({tag: 'node-test-app', facility: 3});
logger.set({tag: 'node-test-app', facility: 'daemon'});

Also you can set TAG, Facility, HOSTNAME, PORT, and transport separately by setTag, setFacility, setHostname, setPort, setTransport and setMessageComposer functions. All of them are chainable too.

You can get all destinations by these properties:

  • tag TAG
  • facility Numerical representation of RFC 3164 facility
  • hostname HOSTNAME
  • port PORT

Custom message composer

var SysLogger = require('ain2');
var console = new SysLogger();

console.setMessageComposer(function(message, severity){
    return new Buffer('<' + (this.facility * 8 + severity) + '>' +
            this.getDate() + ' ' + '[' + + ']:' + message);

//The default implementation looks this:

SysLogger.prototype.composeSyslogMessage = function(message, severity) {
    return new Buffer('<' + (this.facility * 8 + severity) + '>' +
            this.getDate() + ' ' + this.hostname + ' ' + 
            this.tag + '[' + + ']:' + message);


As noticed before ain implements all console functions. Severity level is referenced to RFC 3164:

#  String   Description
0  emerg    Emergency: system is unusable
1  alert    Alert: action must be taken immediately
2  crit     Critical: critical conditions
3  err      Error: error conditions
4  warn     Warning: warning conditions
5  notice   Notice: normal but significant condition
6  info     Informational: informational messages
7  debug    Debug: debug-level messages

Ain console-like functions behaviour is fully compatible to node.js and logs messages with different severity levels:

  • log - notice (5)
  • info - info (6)
  • warn - warn (4)
  • error - err (3)
  • dir - notice (5)
  • time, timeEnd - notice (5)
  • trace - err (3)
  • assert - err (3)

To log a message with the desired severity level you can use the send function:

logger.send('message', 'alert');

The send function takes two arguments: message and optional severity level. By default, the severity level is notice.