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Syslog logging for node.js

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

Ain 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 send messages by UDP to by default, but can also be configured to use a unix datagram socket, eg. /dev/log, although that's a less scalable setup. See RFC 3164.

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

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


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

npm install ain2


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

var console = require('ain2');

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

Changing destinations

By default ain sets following destinations:

  • TAG - __filename
  • Facility - user (1)
  • Severity threshold - 'debug' (lets all messages through)
  • Socket type - udp
  • HOSTNAME - localhost
  • PORT - 514

You can change them by set function. set function is chainable.

var logger = require('ain2')
        .set('node-test-app', 'daemon', 'error', 'udp', 'devhost', 3000);
logger.error('some error');
logger.warn('some warning');

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

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

set function takes up to six arguments, all of which are optional. The first four are always tag, facility, socketType, and severityThreshold. If socketType is specified as udp, the next two arguments will be interpreted as hostname and port. If socketType is unixDatagramSocket, the fourth argument is interpreted as the path of the socket, defaulting to /dev/log.

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 facility by String or Number:

logger.set('node-test-app', 3);
logger.set('node-test-app', 'daemon');

Also you can set TAG, Facility and HOSTNAME separatelly by setTag, setFacility and setHostname functions. All of them is chainable too.

You can get all destinations by theese properties:

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


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 message with desired severity level you can use send function:

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

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

Additional loggers

After importing ain already has default logger. Everything that was described above - just about it.

If you need log message with different TAG, facility and HOSTNAME without touching default logger, you can get independent instance of logger by get function.

var logger = require('ain').set('node-test-app', 'daemon', null, 'udp', 'devhost');
logger.warn('some warning');

var anotherLogger = logger.get(logger.tag, 'local0', null, 'udp', logger.hostname);
anotherLogger.log('another message');

var yetAnotherLogger = logger.get(logger.tag, 'local0', 'warn', 'unixDatagramSocket', '/dev/log');
yetAnotherLogger.log('yet another message');

get function takes three arguments - as well as set function and return new logger object. This object is just new instance of "logger" and has all ain functions (including get).

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