syslog-ng reference manual

Balázs Scheidler

Copyright © 1999-2004 Balázs Scheidler

This manual is free software; you may redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2, or (at your option) any later version.

This is distributed in the hope that it will be useful, but without any
warranty; without even the implied warranty of merchantability or fitness for a
particular purpose. See the GNU General Public License for more details.

-------------------------------------------------------------------------------

Table of Contents
1. Introduction to syslog-ng
2. Message paths

    Sources
    Filters
    Destinations
    Log paths
    Options

3. Reference

    Source drivers

        internal()
        unix-stream() and unix-dgram()
        tcp() and udp()
        file()
        pipe()
        sun-streams() driver

    Destination drivers

        file()
        pipe()
        unix-stream() & unix-dgram()
        udp() & tcp()
        usertty()
        program()

    Filter functions
    Options

4. Performance tuning in syslog-ng

    Setting garbage collector parameters

        gc_idle_threshold()
        gc_busy_threshold()

    Setting output queue size
    Setting sync parameter

List of Tables
2-1. Communication method between syslogd and its clients
2-2. Available source drivers in syslog-ng
2-3. Available destination drivers in syslog-ng
2-4. Log statement flags
3-1. Available options for unix-stream & unix-dgram
3-2. Available options for udp() & tcp()
3-3. Available options for file
3-4. Available options for pipe
3-5. Available options for sun-streams
3-6. Available macros in filename expansion
3-7. Available options for file()
3-8. Available options for pipe()
3-9. Available options for unix-stream() & unix-dgram()
3-10. Available options for udp() & tcp()
3-11. Additional options for tcp()
3-12. Available options for usertty()
3-13. Available options for program()
3-14. Available filter functions in syslog-ng
3-15. List of supported global options in syslog-ng

List of Examples
2-1. Source statement on a Linux based operating system
2-2. A filter statement finding the messages containing the word deny coming
    from the host blurp
3-1. Using the internal() driver
3-2. Using the unix-stream() and unix-dgram() drivers
3-3. Using the udp() and tcp() drivers
3-4. example script to feed a growing logfile into syslog-ng
3-5. Using the file() driver
3-6. Using the pipe() driver
3-7. Using the sun-streams() driver
3-8. Using the file() driver
3-9. Using the file() driver with macros in the file name and a template for
    the message
3-10. Using the pipe() driver
3-11. Using the unix-stream() driver
3-12. Using the tcp() driver
3-13. Using the usertty() driver
3-14. Using the program() destination driver

-------------------------------------------------------------------------------

Chapter 1. Introduction to syslog-ng

One of the most neglected area of Unix is handling system events. Daily checks
for system messages is crucial for the security and health conditions of a
computer system.

System logs contain much "noise" - messages which have no importance - and on
the contrary important events, which should not be lost in the load of
messages. With current tools it's difficult to select which messages we are
interested in.

A message is sent to different destinations based on the assigned facility/
priority pair. There are 12+8 (12 real and 8 local) predefined facilities
(mail, news, auth etc.), and 8 different priorities (ranging from alert to
debug).

One problem is that there are facilities which are too general (daemon), and
these facilities are used by many programs, even if they do not relate each
other. It is difficult to find the interesting bits from the enourmous amount
of messages.

A second problem is that there are very few programs which allow setting their
"facility code" to log under. It's at best a compile time parameter.

So using facilities as a means of filtering is not the best way. For it to be a
good solution would require runtime option for all applications, which
specifies the log facility to log under, and the ability to create new
facilities in syslogd. Neither of these are available, and the first is neither
feasible.

One of the design principles of syslog-ng was to make message filtering much
more finegrained. syslog-ng is able to filter messages based on the contents of
messages in addition to the priority/facility pair. This way only the messages
we are really interested in get to a specific destination. Another design
principle was to make logforwarding between firewalled segments easier: long
hostname format, which makes it easy to find the originating and chain of
forwarding hosts even if a log message traverses several computers. And last
principle was a clean and powerful configuration file format.

-------------------------------------------------------------------------------

Chapter 2. Message paths

In syslog-ng a message path (or message route) consist of one or more sources,
one or more filtering rules and one or more destinations. A message is entered
to syslog-ng in one of its sources, if that message matches the filtering rules
it goes out using the destinations. Note that a message goes to _all_ matching
destinations by default, although this behaviour can be changed.

-------------------------------------------------------------------------------

Sources

A source is a collection of source drivers, which collect messages using a
given method. For instance there's a source driver for AF_UNIX, SOCK_STREAM
style sockets, which is used by the Linux syslog() call.

To declare a source, you'll need to use the source statement in the
configuration file with the following syntax:

          source <identifier> { source-driver(params); source-driver(params); ... };


The identifier has to uniquely identify this given source and of course may not
clash with any of the reserved words (in case you had a nameclash, simply
enclose the identifier in quotation marks)

You can control exactly which drivers are used to gather log messages, thus
you'll have to know how your system and its native syslogd communicate. Here's
a introduction to the inner workings of syslogd on some of the platforms I
tested:

Table 2-1. Communication method between syslogd and its clients

+-----------------------------------------------------------------------------+
| Platform |                              Method                              |
|----------+------------------------------------------------------------------|
|Linux     |A SOCK_STREAM unix socket named /dev/log                          |
|----------+------------------------------------------------------------------|
|BSD       |A SOCK_DGRAM unix socket named /var/run/log                       |
|flavors   |                                                                  |
|----------+------------------------------------------------------------------|
|Solaris   |                                                                  |
|(2.5 or   |An SVR4 style STREAMS device named /dev/log                       |
|below)    |                                                                  |
|----------+------------------------------------------------------------------|
|Solaris   |In addition to the STREAMS device used in versions below 2.6, uses|
|(2.6 or   |a new multithreaded IPC method called door. By default the door   |
|above)    |used by syslogd is /etc/.syslog_door                              |
+-----------------------------------------------------------------------------+

Each possible communication mechanism has the corresponding source driver in
syslog-ng. For instance to open a unix socket with SOCK_DGRAM style
communication you use the driver unix-dgram, the same with SOCK_STREAM style -
as used under Linux - is called unix-stream.

Example 2-1. Source statement on a Linux based operating system

          source src { unix-stream("/dev/log"); internal(); udp(ip(0.0.0.0) port(514)); };


Each driver may take parameters, some of them are required, others are
optional. The required parameters are positional, meaning that they must be
specified in a defined order. A unix-stream() driver has a single required
argument, the name of the socket to listen to, and several optional parameters,
which follow the socket name. Optional arguments can be specified in any order
and must have the form option(value).

Table 2-2. Available source drivers in syslog-ng

+-----------------------------------------------------------------------------+
|        Name        |                      Description                       |
|--------------------+--------------------------------------------------------|
|internal()          |Messages generated internally in syslog-ng              |
|--------------------+--------------------------------------------------------|
|unix-stream()       |Opens the specified unix socket in SOCK_STREAM mode, and|
|                    |listens for messages.                                   |
|--------------------+--------------------------------------------------------|
|unix-dgram()        |Opens the specified unix socket in SOCK_DGRAM mode, and |
|                    |listens for messages.                                   |
|--------------------+--------------------------------------------------------|
|file()              |Opens the specified file, and reads messages.           |
|--------------------+--------------------------------------------------------|
|pipe(), fifo        |Opens the specified named pipe and reads messages       |
|--------------------+--------------------------------------------------------|
|udp()               |Listens on the specified UDP port for messages.         |
|--------------------+--------------------------------------------------------|
|tcp()               |Listens on the specified TCP port for messages.         |
|--------------------+--------------------------------------------------------|
|sun-stream(),       |Opens the specified STREAMS device on Solaris systems,  |
|sun-streams()       |and reads messages.                                     |
+-----------------------------------------------------------------------------+

For a complete descriptions on the above drivers, see Chapter 3

-------------------------------------------------------------------------------

Filters

Filters perform log routing inside syslog-ng. You can write a boolean
expression using internal functions, which has to evaluate to true for the
message to pass.

Filters have also a uniquely identifying name, so you can refer to filters in
your log statements.

Syntax for the filter statement:

          filter <identifier> { expression; };


An expression may contain parentheses, the boolean operators "and", "or" and
"not", and any of the functions listen in Table 3-14.

Example 2-2. A filter statement finding the messages containing the word deny
coming from the host blurp

          filter f_blurp_deny { host("blurp") and match("deny"); };


For a complete description on the above functions, see Chapter 3.

In earlier revisions of syslog-ng there was a special filter identifier,
"DEFAULT", which matched all not-yet-matched messages. This could make your
configuration much simpler and easier to manage. This feature was removed in
syslog-ng 1.5.x, and a more powerful idea was introduced. For more details
consult the Section called Log paths.

-------------------------------------------------------------------------------

Destinations

A destination is where log is sent if filtering rules match. Similarly to
sources, destinations are comprised of one or more drivers, each of which
define how messages are handled. To declare a destination in the configuration
file, you'll need a destination statement, whose syntax is as following:

          destination <identifier> { destination-driver(params); destination-driver(params); ... };


Table 2-3. Available destination drivers in syslog-ng

+-----------------------------------------------------------------------------+
|    Name    |                          Description                           |
|------------+----------------------------------------------------------------|
|file()      |Writes messages to the given file                               |
|------------+----------------------------------------------------------------|
|fifo(), pipe|Writes messages to the given named pipe                         |
|()          |                                                                |
|------------+----------------------------------------------------------------|
|unix-stream |Sends messages to the given unix socket in SOCK_STREAM style    |
|()          |(Linux)                                                         |
|------------+----------------------------------------------------------------|
|unix-dgram()|Sends messages to the given unix socket in SOCK_DGRAM style     |
|            |(BSD)                                                           |
|------------+----------------------------------------------------------------|
|udp()       |Sends messages to specified host and UDP port                   |
|------------+----------------------------------------------------------------|
|tcp()       |Sends messages to specified host and TCP port                   |
|------------+----------------------------------------------------------------|
|usertty()   |Sends messages to specified user if logged in                   |
|------------+----------------------------------------------------------------|
|program()   |Forks and launches given program, and sends messages to its     |
|            |standard input.                                                 |
+-----------------------------------------------------------------------------+
For detailed list of the supported drivers, see Chapter 3.

-------------------------------------------------------------------------------

Log paths

In the previous chapters we learnt how to define sources, filters and
destinations. We'll need to connect those components together, which is
accomplished by the log statement. The needed syntax is here:

          log { source(s1); source(s2); ...
                filter(f1); filter(f2); ...
                destination(d1); destination(d2); ...
                flags(flag1[, flag2...]); };


Any message coming from any of the listed sources, matching the all the filters
are sent to all listed destinations. Log statements are processed in the order
they appear in the config file.

By default all matching log statements are processed, therefore a single log
message might be sent to the same destination several times, given that
destination is listed on several log statements.

This default behaviour can be changed by the flags() parameter.

Table 2-4. Log statement flags

+-----------------------------------------------------------------------------+
|  Flag  |                            Description                             |
|--------+--------------------------------------------------------------------|
|        |This flag means that the processing of log statements ends here.    |
|final   |Note that this doesn't necessarily mean that matching messages will |
|        |be stored once, as they can be matching log statements processed    |
|        |prior the current one.                                              |
|--------+--------------------------------------------------------------------|
|        |This flag makes a log statement 'fallback'. Being a fallback        |
|fallback|statement means that only messages not matching any 'non-fallback'  |
|        |log statements will be dispatched.                                  |
|--------+--------------------------------------------------------------------|
|catchall|This flag means that the source of the message is ignored, only the |
|        |filters are taken into account when matching messages.              |
+-----------------------------------------------------------------------------+

-------------------------------------------------------------------------------

Options

There are several options you can specify, which modifies the behaviour of
syslog-ng. For an exact list of possible options see the Chapter 3. The general
syntax is here:

          options { option1(params); option2(params); ... };


Each option may have parameters, just like in driver specification.

-------------------------------------------------------------------------------

Chapter 3. Reference

This chapter documents the drivers and options you may specify in the
configuration file.

-------------------------------------------------------------------------------

Source drivers

The following drivers may be used in the source statement, as described in the
previous chapter.

-------------------------------------------------------------------------------

internal()

All internally generated messages "come" from this special source. If you want
warnings, errors and notices from syslog-ng itself, you have to include this
source in one of your source statements.

          Declaration: internal()


Syslog-ng will issue a warning upon startup, if this driver is not referenced.

Example 3-1. Using the internal() driver

            source s_local { internal(); };


-------------------------------------------------------------------------------

unix-stream() and unix-dgram()

These two drivers behave similarly: they open the given AF_UNIX socket, and
start listening on them for messages. unix-stream() is primarily used on Linux,
and uses SOCK_STREAM semantics (connection oriented, no messages are lost),
unix-dgram() is used on BSDs, and uses SOCK_DGRAM semantics, this may result in
lost local messages, if the system is overloaded.

To avoid denial of service attacks when using connection-oriented protocols,
the number of simultaneously accepted connections should be limited. This can
be achieved using the max-connections() parameter. The default value of this
parameter is quite strict, you might have to increase it on a busy system.

Both unix-stream and unix-dgram has a single required positional argument,
specifying the filename of the socket to create, and several optional
parameters.

          Declaration:
            unix-stream(filename [options]);
            unix-dgram(filename [options]);


The following options can be specified:

Table 3-1. Available options for unix-stream & unix-dgram

+-----------------------------------------------------------------------------+
|     Name      | Type |                 Description                  |Default|
|---------------+------+----------------------------------------------+-------|
|owner()        |string|Set the uid of the socket.                    |root   |
|---------------+------+----------------------------------------------+-------|
|group()        |string|Set the gid of the socket. Default: root.     |root   |
|---------------+------+----------------------------------------------+-------|
|               |      |Set the permission mask. For octal numbers    |       |
|perm()         |number|prefix the number with '0', e.g. use 0755 for |0666   |
|               |      |rwxr-xr-x.                                    |       |
|---------------+------+----------------------------------------------+-------|
|               |yes or|Selects whether to keep connections opened    |       |
|keep-alive()   |no    |when syslog-ng is restarted, can be used only |yes    |
|               |      |with unix-stream(). Default: yes.             |       |
|---------------+------+----------------------------------------------+-------|
|max-connections|      |Limits the number of simultaneously opened    |       |
|()             |number|connections. Can be used only with unix-stream|10     |
|               |      |().                                           |       |
+-----------------------------------------------------------------------------+

Example 3-2. Using the unix-stream() and unix-dgram() drivers

            # source declaration on Linux
            source s_stream { unix-stream("/dev/log" max-connections(10)); };

            # source declaration on BSDs
            source s_dgram { unix-dgram("/var/run/log"); };



-------------------------------------------------------------------------------

tcp() and udp()

These drivers let you receive messages from the network, and as the name of the
drivers show, you can use both UDP and TCP as transport.

UDP is a simple datagram oriented protocol, which provides "best effort
service" to transfer messages between hosts. It may lose messages, and no
attempt is made to retransmit such lost messages at the protocol level.

TCP provides connection-oriented service, which basically means a
flow-controlled message pipeline. In this pipeline, each message is
acknowledged, and retransmission is done for lost packets. Generally it's safer
to use TCP, because lost connections can be detected, and no messages get lost,
but traditionally the syslog protocol uses UDP.

None of tcp() and udp() drivers require positional parameters. By default they
bind to 0.0.0.0:514, which means that syslog-ng will listen on all available
interfaces, port 514. To limit accepted connections to one interface only, use
the localip() parameter as described below.

    Note: NOTE: the tcp port 514 is reserved for use with rshell, so you have
    to pick another port if you intend to use syslog-ng and rshell at the same
    time.

          Declaration:
            tcp([options]);
            udp([options]);


The following options are valid for udp() and tcp()

Table 3-2. Available options for udp() & tcp()

+-----------------------------------------------------------------------------+
|     Name      | Type |                 Description                  |Default|
|---------------+------+----------------------------------------------+-------|
|ip() or localip|      |The IP address to bind to. Note that this is  |       |
|()             |string|not the address where messages are accepted   |0.0.0.0|
|               |      |from.                                         |       |
|---------------+------+----------------------------------------------+-------|
|port() or      |number|The port number to bind to.                   |514    |
|localport()    |      |                                              |       |
|---------------+------+----------------------------------------------+-------|
|               |yes or|Available for tcp() only, and specifies       |       |
|keep-alive()   |no    |whether to close connections upon the receival|yes    |
|               |      |of a SIGHUP signal.                           |       |
|---------------+------+----------------------------------------------+-------|
|tcp-keep-alive |yes or|Available for tcp() only, and specifies       |       |
|()             |no    |whether to enable TCP keep alive messages     |no     |
|               |      |using the SO_KEEPALIVE socket option.         |       |
|---------------+------+----------------------------------------------+-------|
|max-connections|number|Specifies the maximum number of simultaneous  |10     |
|()             |      |connections.                                  |       |
+-----------------------------------------------------------------------------+

Example 3-3. Using the udp() and tcp() drivers

            source s_tcp { tcp(ip(127.0.0.1) port(1999) max-connections(10)); };
            source s_udp { udp(); };


-------------------------------------------------------------------------------

file()

Usually the kernel presents its messages in a special file (/dev/kmsg on BSDs,
/proc/kmsg on Linux), so to read such special files, you'll need the file()
driver. Please note that you can't use this driver to follow a file like tail
-f does. To feed a growing logfile into syslog-ng (HTTP access.log for
instance), use a script like this:

Example 3-4. example script to feed a growing logfile into syslog-ng

            #!/bin/sh
            tail -f logfile | logger -p local4.info


The file driver has a single required parameter specifying the file to open and
the following options:

Table 3-3. Available options for file

+-----------------------------------------------------------------------------+
|   Name   | Type |                    Description                    |Default|
|----------+------+---------------------------------------------------+-------|
|log_prefix|      |The string to prepend log messages. Useful for     |empty  |
|()        |string|logging kernel messages as it is not prefixed by   |string |
|          |      |'kernel:' by default                               |       |
+-----------------------------------------------------------------------------+

          Declaration:
            file(filename);


Example 3-5. Using the file() driver

            source s_file { file("/proc/kmsg"); };


    Note: NOTE: on Linux, the klogd daemon reads kernel messages, and forwards
    them to the syslogd process. klogd preprocesses kernel messages and
    replaces addresses with symbolic names (from /boot/System.map). If you
    don't want to lose this functionality you'll have to run klogd with
    syslog-ng as well.

-------------------------------------------------------------------------------

pipe()

The pipe driver opens a named pipe with the specified name, and listens for
messages. It's used as the native message getting protocol on HP-UX.

The pipe driver has a single required parameter, specifying the filename of the
pipe to open, and the following options:

Table 3-4. Available options for pipe

+-----------------------------------------------------------------------------+
|  Name  | Type |                     Description                     |Default|
|--------+------+-----------------------------------------------------+-------|
|        |      |Specifies input padding. Some operating systems (such|       |
|pad_size|number|as HP-UX) pad all messages to block boundary. This   |0      |
|()      |      |option can be used to specify the block size. (HP-UX |       |
|        |      |uses 2048 bytes)                                     |       |
+-----------------------------------------------------------------------------+

          Declaration:
            pipe(filename);


NOTE: you'll need to create this pipe using mkfifo(1).

Example 3-6. Using the pipe() driver

            source s_pipe { pipe("/dev/log"); };


-------------------------------------------------------------------------------

sun-streams() driver

Solaris uses its STREAMS API to send messages to the syslogd process. You'll
have to compile syslog-ng with this driver compiled in (see ./configure
--help).

Newer versions of Solaris (2.5.1 and above), uses a new IPC in addition to
STREAMS, called door to confirm delivery of a message. Syslog-ng supports this
new IPC mechanism with the door() option (see below).

The sun-streams() driver has a single required argument, specifying the STREAMS
device to open and a single option.

Example 3-7. Using the sun-streams() driver

              source s_stream { sun-streams("/dev/log" door("/etc/.syslog_door"); };


Table 3-5. Available options for sun-streams

+-----------------------------------------------------------------------------+
|Name | Type |                      Description                       |Default|
|-----+------+--------------------------------------------------------+-------|
|door |string|Specifies the filename of a door to open, needed on     |none   |
|()   |      |Solaris above 2.5.1.                                    |       |
+-----------------------------------------------------------------------------+
-------------------------------------------------------------------------------

Destination drivers

Destination drivers output log messages to somewhere outside syslog-ng: a file
or a network socket.

-------------------------------------------------------------------------------

file()

The file driver is one of the most important destination drivers in syslog-ng.
It allows you to output messages to the named file, or as you'll see to a set
of files.

The destination filename may include macros which gets expanded when the
message is written, thus a simple file() driver may result in several files to
be created. Macros can be included by prefixing the macro name with a '$' sign
(without the quotes), just like in Perl/PHP.

If the expanded filename refers to a directory which doesn't exist, it will be
created depending on the create_dirs() setting (both global and a per
destination option)

Warning: since the state of each created file must be tracked by syslog-ng, it
consumes some memory for each file. If no new messages are written to a file
within 60 seconds (controlled by the time_reap global option), it's closed, and
its state is freed.

Exploiting this, a DoS attack can be mounted against your system. If the number
of possible destination files and its needed memory is more than the amount
your logserver has.

The most suspicious macro is $PROGRAM, where the possible variations is quite
high, so in untrusted environments $PROGRAM usage should be avoided.

Table 3-6. Available macros in filename expansion

+-----------------------------------------------------------------------------+
|  Name  |                            Description                             |
|--------+--------------------------------------------------------------------|
|FACILITY|The name of the facility, the message is tagged as coming from.     |
|--------+--------------------------------------------------------------------|
|PRIORITY|The priority of the message.                                        |
|or LEVEL|                                                                    |
|--------+--------------------------------------------------------------------|
|TAG     |The priority and facility encoded as a 2 digit hexadecimal number.  |
|--------+--------------------------------------------------------------------|
|DATE    |                                                                    |
|--------+--------------------------------------------------------------------|
|FULLDATE|                                                                    |
|--------+--------------------------------------------------------------------|
|ISODATE |                                                                    |
|--------+--------------------------------------------------------------------|
|        |The year the message was sent. Time expansion macros can either use |
|YEAR    |the time specified in the log message, e.g. the time the log message|
|        |is sent, or the time the message was received by the log server.    |
|        |This is controlled by the use_time_recvd() option.                  |
|--------+--------------------------------------------------------------------|
|MONTH   |The month the message was sent.                                     |
|--------+--------------------------------------------------------------------|
|DAY     |The day of month the message was sent.                              |
|--------+--------------------------------------------------------------------|
|WEEKDAY |The 3-letter name of the day of week the message was sent, e.g.     |
|        |'Thu'.                                                              |
|--------+--------------------------------------------------------------------|
|HOUR    |The hour of day the message was sent.                               |
|--------+--------------------------------------------------------------------|
|MIN     |The minute the message was sent.                                    |
|--------+--------------------------------------------------------------------|
|SEC     |The second the message was sent.                                    |
|--------+--------------------------------------------------------------------|
|TZOFFSET|The time-zone as hour offset from GMT. e.g. '-0700'                 |
|--------+--------------------------------------------------------------------|
|TZ      |The time zone or name or abbreviation. e.g. 'PDT'                   |
|--------+--------------------------------------------------------------------|
|FULLHOST|                                                                    |
|--------+--------------------------------------------------------------------|
|        |The name of the source host where the message is originated from. If|
|HOST    |the message traverses several hosts, and chain_hostnames() is on,   |
|        |the first one is used.                                              |
|--------+--------------------------------------------------------------------|
|PROGRAM |The name of the program the message was sent by.                    |
|--------+--------------------------------------------------------------------|
|MSG or  |Message contents including the programname and pid.                 |
|MESSAGE |                                                                    |
|--------+--------------------------------------------------------------------|
|MSGONLY |Message contents without the program name.                          |
+-----------------------------------------------------------------------------+

Table 3-7. Available options for file()

+-----------------------------------------------------------------------------+
|     Name      | Type |               Description                |  Default  |
|---------------+------+------------------------------------------+-----------|
|log_fifo_size()|number|The number of entries in the output fifo. |Use global |
|               |      |                                          |setting.   |
|---------------+------+------------------------------------------+-----------|
|               |yes or|Forces an fsync() call on the destination |           |
|fsync()        |no    |fd after each write. Note: this may       |           |
|               |      |degrade performance seriously             |           |
|---------------+------+------------------------------------------+-----------|
|sync_freq()    |number|The logfile is synced when this number of |Use global |
|               |      |messages has been written to it.          |setting.   |
|---------------+------+------------------------------------------+-----------|
|encrypt()      |yes or|Encrypt the resulting file. NOTE: this is |Use global |
|               |no    |not implemented as of 1.3.14.             |setting.   |
|---------------+------+------------------------------------------+-----------|
|               |yes or|Compress the resulting logfile using zlib.|Use global |
|compress()     |no    |NOTE: this is not implemented as of       |setting.   |
|               |      |1.3.14.                                   |           |
|---------------+------+------------------------------------------+-----------|
|owner()        |string|Set the owner of the created filename to  |root       |
|               |      |the one specified.                        |           |
|---------------+------+------------------------------------------+-----------|
|group()        |string|Set the group of the created filename to  |root       |
|               |      |the one specified.                        |           |
|---------------+------+------------------------------------------+-----------|
|perm()         |number|The permission mask of the file if it is  |0600       |
|               |      |created by syslog-ng.                     |           |
|---------------+------+------------------------------------------+-----------|
|create_dirs()  |yes or|Enable creating non-existing directories. |no         |
|               |no    |                                          |           |
|---------------+------+------------------------------------------+-----------|
|               |      |The permission mask of directories created|           |
|               |      |by syslog-ng. Log directories are only    |           |
|dir_perm()     |number|created if a file after macro expansion   |0600       |
|               |      |refers to a non-existing directory, and   |           |
|               |      |dir creation is enabled using create_dirs |           |
|               |      |().                                       |           |
|---------------+------+------------------------------------------+-----------|
|dir_owner()    |string|The owner of directories created by       |root       |
|               |      |syslog-ng.                                |           |
|---------------+------+------------------------------------------+-----------|
|dir_group()    |string|The group of directories created by       |root       |
|               |      |syslog-ng.                                |           |
|---------------+------+------------------------------------------+-----------|
|               |      |                                          |a format   |
|               |      |Specifies a template which defines the    |conforming |
|template()     |string|logformat to be used in this file.        |to the     |
|               |      |Possible macros are the same as with      |default    |
|               |      |destination file().                       |logfile    |
|               |      |                                          |format.    |
|---------------+------+------------------------------------------+-----------|
|               |      |Turns on escaping ' and " in templated    |           |
|               |      |output files. This is useful for          |           |
|template_escape|yes or|generating SQL statements and quoting     |yes        |
|()             |no    |string contents so that parts of your log |           |
|               |      |message don't get interpreted as commands |           |
|               |      |to the SQL server.                        |           |
|---------------+------+------------------------------------------+-----------|
|               |      |If set to a value higher than 0, before   |           |
|               |      |writing to a file, syslog-ng checks       |           |
|               |      |whether this file is older than the       |Do never   |
|               |      |specified amount of time (specified in    |remove     |
|remove_if_older|      |seconds). If so, it removes the existing  |existing   |
|()             |number|file and the line to be written is the    |files, but |
|               |      |first line in a new file with the same    |append ( = |
|               |      |name. In combination with e.g. the        |0).        |
|               |      |$WEEKDAY macro, this is can be used for   |           |
|               |      |simple log rotation, in case not all      |           |
|               |      |history need to be kept.                  |           |
+-----------------------------------------------------------------------------+

Example 3-8. Using the file() driver

            destination d_file { file("/var/log/messages" ); };


Example 3-9. Using the file() driver with macros in the file name and a
template for the message

            destination d_file {
                    file("/var/log/$YEAR.$MONTH.$DAY/messages"
                            template("$HOUR:$MIN:$SEC $TZ $HOST [$LEVEL] $MSG $MSG\n")
                            template_escape(no)
                    );
            };


-------------------------------------------------------------------------------

pipe()

This driver sends messages to a named pipe like /dev/xconsole

The pipe driver has a single required parameter, specifying the filename of the
pipe to open.

          Declaration:
            pipe(filename);


NOTE: you'll need to create this pipe using mkfifo(1).

Table 3-8. Available options for pipe()

+-----------------------------------------------------------------------------+
|     Name      | Type |              Description               |   Default   |
|---------------+------+----------------------------------------+-------------|
|owner()        |string|Set the owner of the pipe to the one    |root         |
|               |      |specified.                              |             |
|---------------+------+----------------------------------------+-------------|
|group()        |string|Set the group of the pipe to the one    |root         |
|               |      |specified.                              |             |
|---------------+------+----------------------------------------+-------------|
|perm()         |number|The permission mask of the pipe.        |0600         |
|---------------+------+----------------------------------------+-------------|
|               |      |                                        |a format     |
|               |      |Specifies a template which defines the  |conforming to|
|template()     |string|logformat to be used. Possible macros   |the default  |
|               |      |are the same as with destination file().|logfile      |
|               |      |                                        |format.      |
|---------------+------+----------------------------------------+-------------|
|               |      |Turns on escaping ' and " in templated  |             |
|               |      |output files. This is useful for        |             |
|template_escape|yes or|generating SQL statements and quoting   |yes          |
|()             |no    |string contents so that parts of your   |             |
|               |      |log message don't get interpreted as    |             |
|               |      |commands to the SQL server.             |             |
+-----------------------------------------------------------------------------+

Example 3-10. Using the pipe() driver

            destination d_pipe { pipe("/dev/xconsole"); };


-------------------------------------------------------------------------------

unix-stream() & unix-dgram()

This driver sends messages to a unix socket in either SOCK_STREAM or SOCK_DGRAM
mode.

Both drivers have a single required argument specifying the name of the socket
to connect to.

          Declaration:
            unix-stream(filename [options]);
            unix-dgram(filename [options]);


Table 3-9. Available options for unix-stream() & unix-dgram()

+-----------------------------------------------------------------------------+
|     Name      | Type |              Description               |   Default   |
|---------------+------+----------------------------------------+-------------|
|               |      |                                        |a format     |
|               |      |Specifies a template which defines the  |conforming to|
|template()     |string|logformat to be used. Possible macros   |the default  |
|               |      |are the same as with destination file().|logfile      |
|               |      |                                        |format.      |
|---------------+------+----------------------------------------+-------------|
|               |      |Turns on escaping ' and " in templated  |             |
|               |      |output files. This is useful for        |             |
|template_escape|yes or|generating SQL statements and quoting   |yes          |
|()             |no    |string contents so that parts of your   |             |
|               |      |log message don't get interpreted as    |             |
|               |      |commands to the SQL server.             |             |
+-----------------------------------------------------------------------------+

Example 3-11. Using the unix-stream() driver

            destination d_unix_stream { unix-stream("/var/run/logs"); };


-------------------------------------------------------------------------------

udp() & tcp()

This driver sends messages to another host on the local intranet or internet
using either UDP or TCP protocol.

Both drivers have a single required argument specifying the destination host
address, where messages should be sent, and several optional parameters. Note
that this differs from source drivers, where local bind address is implied, and
none of the parameters are required.

          Declaration:
            tcp(host [options]);
            udp(host [options]);


Table 3-10. Available options for udp() & tcp()

+-----------------------------------------------------------------------------+
|     Name      | Type |                Description                | Default  |
|---------------+------+-------------------------------------------+----------|
|localip()      |string|The IP address to bind to before connecting|0.0.0.0   |
|               |      |to target.                                 |          |
|---------------+------+-------------------------------------------+----------|
|localport()    |number|The port number to bind to.                |0         |
|---------------+------+-------------------------------------------+----------|
|port() or      |number|The port number to connect to.             |514       |
|destport()     |      |                                           |          |
|---------------+------+-------------------------------------------+----------|
|               |      |                                           |a format  |
|               |      |Specifies a template which defines the     |conforming|
|template()     |string|logformat to be used. Possible macros are  |to the    |
|               |      |the same as with destination file().       |default   |
|               |      |                                           |logfile   |
|               |      |                                           |format.   |
|---------------+------+-------------------------------------------+----------|
|               |      |Turns on escaping ' and " in templated     |          |
|template_escape|yes or|output. This is useful for generating SQL  |          |
|()             |no    |statements and quoting string contents so  |yes       |
|               |      |that parts of your log message don't get   |          |
|               |      |interpreted as commands to the SQL server. |          |
|---------------+------+-------------------------------------------+----------|
|tcp-keep-alive |yes or|Available for tcp() only, and specifies    |          |
|()             |no    |whether to enable TCP keep alive messages  |no        |
|               |      |using the SO_KEEPALIVE socket option.      |          |
|---------------+------+-------------------------------------------+----------|
|               |      |Enables source address spoofing. This means|          |
|               |      |that the host running syslog-ng generates  |          |
|               |      |UDP packets with the source IP address     |          |
|               |      |matching the original sender of the        |          |
|               |      |message. It is useful when you want to     |          |
|               |      |perform some kind of preprocessing via     |          |
|spoof_source   |yes or|syslog-ng then forward messages to your    |no        |
|               |no    |central log management solution with the   |          |
|               |      |source address of the original sender. This|          |
|               |      |option only works for UDP destinations     |          |
|               |      |though the original message can be received|          |
|               |      |by TCP as well. This option is only        |          |
|               |      |available if syslog-ng was compiled using  |          |
|               |      |the --enable-spoof-source configure option.|          |
+-----------------------------------------------------------------------------+

Table 3-11. Additional options for tcp()

+-----------------------------------------------------------------------------+
|Name| Type |                       Description                       |Default|
|----+------+---------------------------------------------------------+-------|
|sync|number|The messages are sent to the remote host when this number|0      |
|()  |      |of messages have been collected.                         |       |
+-----------------------------------------------------------------------------+

Example 3-12. Using the tcp() driver

            destination d_tcp { tcp("10.1.2.3" port(1999); localport(999)); };


-------------------------------------------------------------------------------

usertty()

This driver writes messages to the terminal of a logged-in user.

The usertty driver has a single required argument, specifying a username who
should receive a copy of matching messages, and no optional arguments.

          Declaration:
            usertty(username);


Table 3-12. Available options for usertty()

+-----------------------------------------------------------------------------+
|     Name      | Type |              Description               |   Default   |
|---------------+------+----------------------------------------+-------------|
|               |      |                                        |a format     |
|               |      |Specifies a template which defines the  |conforming to|
|template()     |string|logformat to be used. Possible macros   |the default  |
|               |      |are the same as with destination file().|logfile      |
|               |      |                                        |format.      |
|---------------+------+----------------------------------------+-------------|
|               |      |Turns on escaping ' and " in templated  |             |
|               |      |output. This is useful for generating   |             |
|template_escape|yes or|SQL statements and quoting string       |yes          |
|()             |no    |contents so that parts of your log      |             |
|               |      |message don't get interpreted as        |             |
|               |      |commands to the SQL server.             |             |
+-----------------------------------------------------------------------------+

Example 3-13. Using the usertty() driver

            destination d_usertty { usertty("root"); };


-------------------------------------------------------------------------------

program()

This driver fork()'s executes the given program with the given arguments and
sends messages down to the stdin of the child.

The program driver has a single required parameter, specifying a program name
to start and no options. The program is executed with the help of the current
shell, so the command may include both file patterns and I/O redirection, they
will be processed.

          Declaration:
            program(commandtorun);


    Note: NOTE: the program is executed once at startup, and kept running until
    SIGHUP or exit. The reason is to prevent starting up a large number of
    programs for messages, which would imply an easy DoS.

Table 3-13. Available options for program()

+-----------------------------------------------------------------------------+
|     Name      | Type |              Description               |   Default   |
|---------------+------+----------------------------------------+-------------|
|               |      |                                        |a format     |
|               |      |Specifies a template which defines the  |conforming to|
|template()     |string|logformat to be used. Possible macros   |the default  |
|               |      |are the same as with destination file().|logfile      |
|               |      |                                        |format.      |
|---------------+------+----------------------------------------+-------------|
|               |      |Turns on escaping ' and " in templated  |             |
|               |      |output. This is useful for generating   |             |
|template_escape|yes or|SQL statements and quoting string       |yes          |
|()             |no    |contents so that parts of your log      |             |
|               |      |message don't get interpreted as        |             |
|               |      |commands to the SQL server.             |             |
+-----------------------------------------------------------------------------+

Example 3-14. Using the program() destination driver

            destination d_prg { program("/bin/cat >/dev/null"); };


-------------------------------------------------------------------------------

Filter functions

The following functions may be used in the filter statement, as described in
the previous chapter.

Table 3-14. Available filter functions in syslog-ng

+-----------------------------------------------------------------------------+
|   Name    |    Synopsis    |                  Description                   |
|-----------+----------------+------------------------------------------------|
|facility   |facility(faciliy|Match messages having one of the listed facility|
|           |[,facility])    |code.                                           |
|-----------+----------------+------------------------------------------------|
|level() or |level(pri       |                                                |
|priority() |[,pri1..pri2    |Match messages based on priority.               |
|           |[,pri3]])       |                                                |
|-----------+----------------+------------------------------------------------|
|program()  |program(regexp) |Match messages by using a regular expression    |
|           |                |against the program name field of log messages  |
|-----------+----------------+------------------------------------------------|
|host()     |host(regexp)    |Match messages by using a regular expression    |
|           |                |against the hostname field of log messages.     |
|-----------+----------------+------------------------------------------------|
|match()    |match(regexp)   |Tries to match a regular expression to the      |
|           |                |message itself.                                 |
|-----------+----------------+------------------------------------------------|
|filter()   |filter          |Call another filter rule and evaluate its value |
|           |(filtername)    |                                                |
|-----------+----------------+------------------------------------------------|
|netmask()  |netmask(ip/mask)|Check the sender's IP address whether it is in  |
|           |                |the specified IP subnet                         |
+-----------------------------------------------------------------------------+

-------------------------------------------------------------------------------

Options

The following options can be specified in the options statement, as described
in the previous chapter.

Table 3-15. List of supported global options in syslog-ng

+-----------------------------------------------------------------------------+
|         Name          | Accepted |               Description                |
|                       |  values  |                                          |
|-----------------------+----------+------------------------------------------|
|time_reopen()          |number    |The time to wait before a died connection |
|                       |          |is reestablished                          |
|-----------------------+----------+------------------------------------------|
|time_reap()            |number    |The time to wait before an idle           |
|                       |          |destination file is closed.               |
|-----------------------+----------+------------------------------------------|
|sync()                 |number    |The number of lines buffered before       |
|                       |          |written to file                           |
|-----------------------+----------+------------------------------------------|
|mark()                 |number    |The number of seconds between two MARK    |
|                       |          |lines. NOTE: not implemented yet.         |
|-----------------------+----------+------------------------------------------|
|stats()                |number    |The number of seconds between two STATS.  |
|-----------------------+----------+------------------------------------------|
|log_fifo_size()        |number    |The number of lines fitting to the output |
|                       |          |queue                                     |
|-----------------------+----------+------------------------------------------|
|chain_hostnames()      |yes or no |Enable or disable the chained hostname    |
|                       |          |format.                                   |
|-----------------------+----------+------------------------------------------|
|keep_hostname()        |yes or no |Enable or disable hostname rewriting.     |
|-----------------------+----------+------------------------------------------|
|check_hostname()       |yes or no |Enable or disable whether the hostname    |
|                       |          |contains valid characters.                |
|-----------------------+----------+------------------------------------------|
|bad_hostname()         |regular   |A regexp which matches hostnames which    |
|                       |expression|should not be taken as such.              |
|-----------------------+----------+------------------------------------------|
|create_dirs()          |yes or no |Enable or disable directory creation for  |
|                       |          |destination files.                        |
|-----------------------+----------+------------------------------------------|
|owner()                |userid    |.                                         |
|-----------------------+----------+------------------------------------------|
|group()                |groupid   |.                                         |
|-----------------------+----------+------------------------------------------|
|perm()                 |permission|.                                         |
|                       |value     |                                          |
|-----------------------+----------+------------------------------------------|
|dir_owner()            |userid    |.                                         |
|-----------------------+----------+------------------------------------------|
|dir_group()            |groupid   |.                                         |
|-----------------------+----------+------------------------------------------|
|dir_perm()             |permission|.                                         |
|                       |value     |                                          |
|-----------------------+----------+------------------------------------------|
|use_time_recvd()       |yes or no |Use the time a message is received instead|
|                       |          |of the one specified in the message.      |
|-----------------------+----------+------------------------------------------|
|                       |          |Enable or disable DNS usage. syslog-ng    |
|                       |          |blocks on DNS queries, so enabling DNS may|
|                       |          |lead to a Denial of Service attack. To    |
|use_dns()              |yes or no |prevent DoS, protect your syslog-ng       |
|                       |          |network endpoint with firewall rules, and |
|                       |          |make sure that all hosts, which may get to|
|                       |          |syslog-ng is resolvable.                  |
|-----------------------+----------+------------------------------------------|
|dns_cache()            |yes or no |Enable or disable DNS cache usage.        |
|-----------------------+----------+------------------------------------------|
|dns_cache_size()       |number    |Number of hostnames in the DNS cache.     |
|-----------------------+----------+------------------------------------------|
|dns_cache_expire()     |number    |Number of seconds while a successful      |
|                       |          |lookup is cached.                         |
|-----------------------+----------+------------------------------------------|
|dns_cache_expire_failed|number    |Number of seconds while a failed lookup is|
|()                     |          |cached.                                   |
|-----------------------+----------+------------------------------------------|
|log_msg_size()         |number    |Maximum length of message in bytes.       |
|-----------------------+----------+------------------------------------------|
|use_fqdn()             |yes or no |Add Fully Qualified Domain Name instead of|
|                       |          |short hostname.                           |
|-----------------------+----------+------------------------------------------|
|                       |          |Sets the threshold value for the garbage  |
|gc_idle_threshold()    |number    |collector, when syslog-ng is idle. GC     |
|                       |          |phase starts when the number of allocated |
|                       |          |objects reach this number. Default: 100.  |
|-----------------------+----------+------------------------------------------|
|                       |          |Sets the threshold value for the garbage  |
|gc_busy_threshold()    |number    |collector, when syslog-ng is busy. GC     |
|                       |          |phase starts when the number of allocated |
|                       |          |objects reach this number. Default: 3000. |
+-----------------------------------------------------------------------------+

-------------------------------------------------------------------------------

Chapter 4. Performance tuning in syslog-ng

There are several settings available you can finetune the behaviour of
syslog-ng. The defaults should be adequate for a single server or workstation
installation, but for a central loghost receiving the logs from multiple
computers it may not be enough.

-------------------------------------------------------------------------------

Setting garbage collector parameters

Syslog-ng uses a garbage collector internally, and while the garbage collector
is running it does not accept messages. This may cause problems if some
non-connection oriented transport protocol is used, like unix-dgram() or udp().
There are two settings which control the garbage collection phase:

-------------------------------------------------------------------------------

gc_idle_threshold()

With this option you can specify the idle threshold of the gc. If the number of
allocated objects reach this number, and the system is idle (no message arrived
within 100msec), a gc phase starts. Since the system is idle, presumably no
messages will be lost if the gc is ran. Therefore this value should be low, but
higher than the minimally allocated objects. The minimum number of objects
allocated depends on your configuration, but you can get exact numbers by
specifying the -v command line option.

-------------------------------------------------------------------------------

gc_busy_threshold()

This threshold is used when syslog-ng is busy accepting messages (this means
that within 100msec an I/O event occured), however to prevent syslog-ng eating
all your memory, gc should be ran in these cases as well. Set this value high,
so that your log bursts don't get interrupted by the gc.

-------------------------------------------------------------------------------

Setting output queue size

Syslog-ng always reads its incoming log channels to prevent your running
daemons from blocking. This may result in lost messages if the output queue is
full. It's therefore important to set the output queue size (termed in number
of messages), which you can do globally, or on a per destination basis.

          options { log_fifo_size(1000); };


or

          destination d_messages { file("/var/log/messages" log_fifo_size(1000); };


You should set your fifo size to the estimated number of messages in a message
burst. If bursts extend the bandwidth of your destination pipe, syslog-ng can
feed messages into the destination pipe after the burst has collapsed.

Of course syslog-ng cannot widen your network bandwidth, so if your destination
host lives on a noisy network, and your logtraffic extends the bandwidth of
this network, syslog-ng can't do anything. It'll do its best however.

-------------------------------------------------------------------------------

Setting sync parameter

The sync parameter doesn't exactly do what you might expect. As you have seen
messages to be sent are buffered in an output queue. The sync parameter
specifies the number of messages held in this buffer before anything is
written.

Note that it doesn't write all buffered messages in one single chunk, it writes
each distinct message with a single write() system call.

