Syslog4j FAQ
Version:  $Id: faq.html,v 1.17 2010/09/11 16:49:23 cvs Exp $
URL:      http://www.syslog4j.org/

1. General

1.1.  What is Syslog4j?

Syslog4j is a pure-Java implementation of the syslog client and server
specification as defined by "The BSD syslog Protocol" (RFC3164) with
additional support for TCP/IP-based syslog, native Unix syslog, and
Unix sockets.

Java applications (web or otherwise) needing to log messages to a syslog
server or Java applications needing to accept syslog messages can use

1.2.  Doesn't a Java syslog client already exist?

Not really.  Various Internet searches present a few options, but no
officially-supported solutions seem to exist (as of October 2008).

One solution is found at http://www.trustice.com/java/syslog/ but it
appears (as of this writing) that the code has not been updated since
2001, and attempting to download the distributions sometimes
results in errors.

JavaWorld has a posting about syslog from 2001 here:

Several quick-and-dirty UDP-based code examples are also available via
Internet searches.

1.3.  Why use Syslog4j?

It's easy and extensible!

Syslog4j provides UDP, TCP, Native Unix syslog, and Unix socket logging
with a simplified interface and is designed using an extensible coding
model that allows developers to improve upon or add new capabilities.

Of course, it's recommended any improvements are submitted to the Syslog4j
developers so Syslog4j can continually evolve.

1.4.  What dependencies are required for Syslog4j?

Syslog4j requires JDK 1.4 or higher and requires NO EXTERNAL
LIBRARIES (JARs) for basic UDP/IP and TCP/IP clients and servers.

Unix syslog and/or Unix sockets require the JNA library,
available at: https://jna.dev.java.net/

Pooled connections for TCP/IP and TCP/IP over SSL/TLS
require the Apache Commons Pool library available
at: http://commons.apache.org/pool/

Log4j support requires, well, Apache Log4j, available at:

1.5.  Is Syslog4j cross-platform?

Yes!  Syslog4j UDP/IP and TCP/IP clients should work in any
typical Java JRE environment.

1.6.  How do I use Native Unix syslog or Unix sockets?

Because the Java JRE does not contain support for Unix syslog and
Unix socket logging, Syslog4j requires "hooks" into operating
system-specific libraries, and thus the JNA library is required.

The JNA library is available here:


This was chosen in lieu of JNI, which requires operating system-
specific code to support the native library calls.  JNA provides
a stand-alone JAR without any need for any additional libraries.

1.7.  Which license does Syslog4j use?

Syslog4j is released as free software under the Lesser GNU Public
License v2.1, defined at the following URL:

Additionally, the Open Source Initiative (OSI) lists the LGPL license in
its directory of accepted open source licenses, here:

A copy of the LGPLv2 is made available in the META-INF directory of the
Syslog4j JAR distributions in a file called LICENSE.txt.

This license is used by a large number of library-oriented projects on
the Internet, including the largely popular "Hibernate" persistence


2.  Syslog4j Use & Examples

2.1.  Where do I obtain Syslog4j?

Syslog4j is available here:

2.2.  There seem to be several choices for download.  Which one do I use?

Every release, there are four different JAR distributions and one
ZIP document distribution for Syslog4j:

  Binary + Source Distribution:  syslog4j-x.y.z.jar
  Binary Distribution:           syslog4j-x.y.z-bin.jar
  Source Distribution:           syslog4j-x.y.z-src.jar
  JUnit (Test) Distribution:     syslog4j-x.y.z-junit.jar
  Documentation Distribution:    syslog4j-x.y.z-doc.zip

To get started, it is recommended that you use the "Binary + Source"
distribution, as it (a) is compiled with the javac "debug" flag and
(b) allow you access to the Syslog4j source code for ease in debugging. 

If you have concerns about performance or including source code in your
application, you're welcome to use the "Binary" Distribution.  It is
compiled without the javac "debug" flag and the source code is not
included within the JAR file. 

If you wish to compile your own Syslog4j from the source code, the
"Source" distribution is your best choice.

If you'd like to JUnit test Syslog4j or see working code examples,
the "JUnit (Test)" distribution will be of interest to you.  Source
code for the JUnit tests are included in this distribution.

The "Documentation" distribution contains the API (JavaDoc), this
document (the FAQ), and other potentially useful information. 

2.3.  How do I start using Syslog4j?

For syslog clients, start with the singleton class called "Syslog"
(org.productivity.java.syslog4j.Syslog).  This class provides access to
get existing instances and create new instances of Syslog4j "protocols."

For syslog servers, start with the singleton class called "SyslogServer"

2.4.  What is a Syslog4j "protocol"?

This is a String that defines the actual underlying Syslog4j
implementation you wish to use.  Syslog4j comes "ready to run" with
the following stock protocols:

  "udp" -- The original syslog "UDP" protocol, pointed to
           (localhost), configured to use the "USER" syslog facility.
  "tcp" -- An implementation of the de-facto TCP/IP syslog protocol,
           which points to a TCP-capable syslog server, defaulted to
  (localhost), configured to use the "USER" syslog
  "unix_syslog" -- Native syslog support for Unix platforms, configured
           to use the "USER" syslog facility.
  "unix_socket" -- Native socket support for Unix platforms, pointed to
           the "/var/log" socket, configured to use the "USER" syslog
2.5.  How do I use one of the stock protocols?

There are two ways -- the "direct" way and the "via an interface" way, shown

// Direct UDP Use Example
Syslog.getInstance("udp").info("This is an INFO level log entry.");

// Via an Interface UDP Use Example
SyslogIF syslog = Syslog.getInstance("udp");
syslog.info("This is another INFO level log entry.");

To use "tcp" protocol, simply switch the "udp" above to:  "tcp"

2.6.  How do I point one of the stock protocols to go to a particular
      host or port?
There are two ways -- the "direct" way and the "via an interface" way, shown

// Direct UDP Config Example

// Via an Interface UDP Config Example
SyslogConfigIF config = Syslog.getInstance("udp").getConfig();

2.7.  How do I send messages to more than one syslog server?

The stock protocols in Syslog4j are designed as a convenience for those
that need to send to one server only.  To point to more than one syslog
server, it's recommended that you create your own custom Syslog4j

MultipleSyslog is an aggregate protocol that can be used to send
the same log entries to multiple stock or custom protocols.

2.8.  How do I create my own custom Syslog4j protocol?

Syslog4j uses the coding paradigm of "dependency injection."  In this
model, you create a Syslog4j configuration object and feed this object
to the Syslog.createInstance(protocol,config) method.

Here's an example, creating a new "audit" protocol which uses a UDP
implementation under the scenes:

// Syslog4j Protocol Configuration Creation Example
SyslogConfigIF config = new UDPNetSyslogConfig();

// Syslog4j Instance Creation Example

This new "audit" instance is pointed to a specific server -- in
this case "auditsyslog.example.com" -- and is configured to use
the "LOCAL7" syslog facility.

Since you've created a new instance, the original stock "udp"
instance is not affected and can still be used.

2.9.  How do I use my own custom Syslog4j protocol?

The Syslog.createInstance(protocol,config) method returns the
SyslogIF implementation if you'd like to use the Syslog4j right away:

// Syslog4j Instance Creation Example
SyslogIF syslog = Syslog.createInstance("audit",config);
syslog.info("This is the first INFO entry to this Syslog4j protocol.");

But normally, you'll be calling Syslog4j from other areas of your
code, so use the "direct" or "instances" ways as previously described:

// Custom UDP Syslog4j Protocol Direct Example
Syslog.getInstance("audit").info("This is an INFO entry");

// Custom UDP Syslog4j Protocol Instance Example
SyslogIF syslog = Syslog.getInstance("audit");
syslog.info("This is an INFO entry to the auditsyslog server");

2.10.  How do I close a client protocol connection?

UDP/IP-based, Unix socket, and Unix syslog client protocols do not need
to be explicitly closed.

TCP/IP-based (including SSL/TLS) can be explicitly closed by calling
the flush() method, as follows:

// Flush the TCP/IP Protocol

2.11.  How do I properly shut down all client protocols?

Applications which use only UDP/IP-based, Unix socket, and/or Unix
syslog client protocols do not need to be explicitly closed.

When shutting down a servlet-based application, it's a good idea to
call Syslog.shutdown() in the servlet's destroy() method.  Calling
Syslog.shutdown() ensures that all client connections close properly.

When calling Syslog4j from a standalone Java application, it's a good
idea to both call a small Thread.sleep(..), say 500 milliseconds or so,
and then call Syslog.shutdown().  JUnit tests can also benefit from
this sort of paused shutdown.

2.12.  How do I run a command-line syslog client with Syslog4j?

To access the syslog client, run this (substituting the appropriate
version for x.y.z):

  java -cp syslog4j-x.y.z.jar org.productivity.java.syslog4j.SyslogMain

...or (alternately) this shortcut technique:

  java -jar syslog4j-x.y.z.jar
Running one of the above commands will provide a list of command-line
options.  Here's an example which sends a UDP/IP test message to a host
located at on port 5555:

  java -jar syslog4j-x.y.z.jar -h -p 5555 udp "test"

Only the stock protocols are currently supported in the Syslog4j command-
line client.

2.13.  How do I run a command-line syslog server with Syslog4j?

Running a command-line syslog server is extremely handy when trouble-
shooting your application.  Run this to get a list of command-line
options (type all of this on one line):

  java -cp syslog4j-x.y.z.jar
Here's an example which waits for requests on port 5555 and displays
the output to standard out:

  java -cp syslog4j-x.y.z.jar
    org.productivity.java.syslog4j.server.SyslogServerMain -p 5555

To test it, open another window/shell and run the following:

  java -jar syslog4j-x.y.z.jar -p 5555 udp "test"

...which should show the message in the server window/shell.

The command-line Syslog server can also write to a file using the -o
option.  However, it's recommended to not use the command-line
syslog server for production purposes; you're best to look into
solutions such as syslog-ng from Balabit IT Security for a robust
syslog server implementation.
Only the "udp" and "tcp" protocols are currently supported in the Syslog4j
command-line server.


3.  Syslog4j and Apache Log4j (http://logging.apache.org/log4j/)

3.1.  Is Syslog4j meant to replace Log4j?

Absolutely not!  Log4j is a robust and complete logging solution.

Syslog4j is meant as a low-level implementation of the syslog
protocol, and not designed to serve as a replacement to Log4j.

3.2.  Wait, doesn't Log4j come with a syslog appender?

In fact, it does!  If an application already uses Log4j, the appender
class of org.apache.log4j.net.SyslogAppender may suit the
majority of UDP-based syslog messaging and Syslog4j isn't needed.

3.3.  So why would I bother using Syslog4j if I already use Log4j?

Syslog4j provides support for protocols other than UDP, which is
the only network protocol supported by the Log4j's SyslogAppender.

The SyslogAppender provided by Log4j is hard-coded to use the
standard syslog port 514 with a maximum message size of 1024
bytes and currently does not support Structured Syslog messages
as per RFC 5424.

3.4.  How do I use Syslog4j with Log4j?

Syslog4j provides a Log4j appender called "Syslog4jAppender," not
to be confused with "SyslogAppender," which comes stock with Log4j.

The Syslog4jAppender allows you to use all Syslog4j protocols
within Log4j.  This includes stock and custom protocols.

3.5.  How do I configure Log4j to use the Syslog4jAppender?

Here is an example log4j.xml entry, which uses the Syslog4j stock "udp"

   <appender name="Syslog4j" class="org.productivity.java.syslog4j.impl.log4j.Syslog4jAppender">
		<param name="Protocol" value="udp"/>
		<param name="Facility" value="user"/>
		<param name="SyslogHost" value=""/>
		<layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern" value="%d{ABSOLUTE} %-5p [%c{1}] %m"/>

To use a custom Syslog4j configuration, simply create your own Syslog4j
protocol with Syslog.createInstance(protocol,config) and configure the
log4j.xml "Protocol" parameter as your chosen "protocol" name.

4.  PCI DSS Audit Logging with Syslog4j

4.1.  What is PCI DSS?


"The PCI DSS, a set of comprehensive requirements for enhancing payment
account data security, was developed by the founding payment brands of
the PCI Security Standards Council, including American Express,
DiscoverFinancial Services, JCB International, MasterCard Worldwide and
Visa Inc. Inc. International, to help facilitate the broad adoption of
consistent data security measures on a global basis.

The PCI DSS is a multifaceted security standard that includes
requirements for security management, policies, procedures, network
architecture, software design and other critical protective measures.
This comprehensive standard is intended to help organizations proactively
protect customer account data."

4.2.  What is PCI DSS Audit Logging?

Section 10.3 of the PCI DSS specification (pages 46-47 of version 1.2,
published in October 2008) requires the following fields be logged
for audit purposes:

 10.3.1  User Identification
 10.3.2  Type of event
 10.3.3  Date and time
 10.3.4  Success or failure indication
 10.3.5  Origination of event
 10.3.6  Identity or name of affected data, system component, or resource
4.3.  How does Syslog4j facilitate PCI DSS Audit Logging?

Syslog4j provides a Java object named PCISyslogMessage which conveniently
handles these fields.

4.4.  How do I use PCISyslogMessage?

PCISyslogMessage has several constructors which cover some or all of the
fields in PCI DSS section 10.3.  An example using the appId, userId,
eventType, status, and affectedId fields is shown below:

// Create a PCISyslogMessage
PCISyslogMessage message =
  new PCISyslogMessage("myapp","jsmith","login","success","jsmith");

// Log the PCISyslogMessage

PCISyslogMessage can also be constructed with (1) a Map object with
key/value pairs containing the above fields, or (2) an object
implementing the PCISyslogMessageIF interface, or (3) the default
constructor.  PCISyslogMessage provides standard "Javabean" getters
and setters for all PCI DSS audit fields.
5.  Miscellaneous

5.1.  Who designed the Syslog4j logo?

Tom Spence designed the excellent Syslog4j logo based on a written
description of the project.  Thanks, Tom!

You can contact Tom and see his other art at:  http://growtreeisland.com