# syslog-ng v2.0 reference manual

### Balázs Scheidler

@VERSION@ (@SOURCE_REVISION@)

Copyright © 1999-2006 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.

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. Common options for source drivers
3.2. Available options for unix-stream() and unix-dgram()
3.3. Available options for tcp(), tcp6(), udp(), and udp6()
3.4. Available options for sun-streams
3.5. Common options for destination drivers
3.6. Available options for file()
3.7. Available options for pipe()
3.8. Available options for unix-stream() and unix-dgram()
3.9. Available options for udp(), udp6(), tcp() and tcp6()
3.10. Available filter functions in syslog-ng
3.11. Available macros in filename expansion
3.12. List of global options supported 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 'foo'
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. 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 having no importance - and important events which should not be lost in the tide of messages. With the current tools it is difficult to select which messages are interesting.

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 priorities (ranging from alert to debug).

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

A second problem is that there are very few programs which allow setting their "facility code" to use for logging. It is at best a compile time parameter.

Consequently, using facilities as a means of filtering is not an optimal approach. A better solution would be to make the syslog facility a runtime option for all applications, and add the ability to create new facilities in syslogd. Neither of these are available; the first one is not even 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 really important messages are sent to a specific destination. Another design principle was to make log forwarding between firewalled segments easier using long hostname format, which makes it easy to find the originating and the chain of forwarding hosts - even if a log message traverses several computers. The last principle was a clean and powerful configuration file format.

## 1. Timezone handling

One of the new features of syslog-ng 2.0 is the support for messages originating from different timezones. This is a difficult problem, as the original syslog protocol does not include timezone information. syslog-ng provides a solution by extending the syslog protocol to include this information and also by giving finegrained control to the administrator to supply timezone information for legacy devices which do not support the protocol extension.

Timezone information is associated with messages entering syslog-ng using the following algorithm:

1. The sender can specify the timezone of the messages. If the incoming message includes a timezone it is associated with the message. Otherwise, the local timezone is assumed.

2. The administrator specifies the `time_zone()` parameter for the source driver that reads the message. This parameter overrides the original timezone of the message. Each source defaults to the value of the `recv_time_zone()` global option.

3. The destination driver specifies the timezone via the `time_zone()` parameter. Each destination driver might have an associated timezone value to which message timestamps are converted before they are sent to the final destination (file or network socket). Each destination defaults to the value of the `send_time_zone()` global option. A message can be sent to multiple destination zones.

4. When macro expansions are used in the destination filenames, the local timezone is used.

There is another case when message timestamps are formatted:

## Chapter 2. Global objects

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 is sent to the specified destinations. Note that a message goes to all matching destinations by default, although this behavior can be changed.

## 1. Sources

A source is a set of source drivers collecting messages using a given method. For instance, there is a source driver for `AF_UNIX`, `SOCK_STREAM` style sockets, used by the Linux `syslog()` call.

To declare a source, the source statement has to be used in the configuration file with the following syntax:

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

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

You can control exactly which drivers are used to gather log messages, thus you have to know how your system and its native `syslogd` communicate. Below is an introduction to the inner workings of `syslogd` on some of the tested platforms:

Table 2.1. Communication method between syslogd and its clients

Platform | Method
--- | ---
Linux | A `SOCK_STREAM` unix socket named `/dev/log`; some of the distributions layers switched over to using `SOCK_DGRAM`, though applications still work with either method.
BSD flavors | A `SOCK_DGRAM` unix socket named `/var/run/log`.
Solaris (2.5 or below) | An SVR4 style `STREAMS` device named `/dev/log`.
Solaris (2.6 or above) | In addition to the `STREAMS` device used in earlier versions, 2.6 uses a new multithreaded IPC method called door. By default the door 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 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 using the `option(value)` syntax.

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.
tcp() | Listens on the specified TCP port for messages.
udp() | Listens on the specified UDP port for messages.
tcp6() | Listens on the specified TCP port for messages over IPv6.
udp6() | Listens on the specified UDP port for messages over IPv6.
sun-stream(), sun-streams() | Opens the specified `STREAMS` device on Solaris systems and reads messages.

For a complete descriptions on the above drivers, see Section 1, “Source drivers”.

## 2. Filters

Filters perform log routing within syslog-ng. You can write a boolean expression using internal functions: a message passes if the expression is true.

Filters also have a unique identifying name that can be referenced in 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 listed in Table 3.10, “Available filter functions in syslog-ng”.

Example 2.2. A filter statement finding the messages containing the word 'deny' coming from the host 'foo'

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

For a complete description on the above functions, see Section 3, “Filter functions”.

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 Section 5, “Log paths”.

## 3. Destinations

A destination is where a log is sent if the filtering rules match. Similarly to sources, destinations are comprised of one or more drivers, each defining how messages are handled. Destinations can be declared in the configuration file via a destination statement using the syntax below:

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

### Note

The list of drivers may be empty: in this case all messages sent to the destination are discarded. This is equivalent to omitting the destination from the log statement.

Table 2.3. Available destination drivers in syslog-ng

Name | Description
--- | ---
file() | Writes messages to the specified file.
fifo(), pipe() | Writes messages to the specified named pipe.
unix-stream() | Sends messages to the specified unix socket in `SOCK_STREAM` style (Linux).
unix-dgram() | Sends messages to the specified unix socket in `SOCK_DGRAM` style (BSD).
tcp() | Sends messages to the specified host and TCP port.
udp() | Sends messages to the specified host and UDP port.
tcp6() | Sends messages to the specified host and TCP port over IPv6.
udp6() | Sends messages to the specified host and UDP port over IPv6.
usertty() | Sends messages to the specified user's terminal if logged in.
program() | Forks and launches the specified program, and sends messages to its standard input.

For detailed description of the supported drivers, see Section 2, “Destination drivers”.

## 4. Template objects

syslog-ng 2.0 allows you to define common templates, and refer to them from every object requiring a template. For example:

              template t_filetmpl { template("$ISODATE $HOST $MSG\n"); template_escape(no)); };

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

Templates can reference one or more macros as described in Section 4, “Macros”.

### Note

Previous versions of syslog-ng required template formats to be defined for every destination.

## 5. Log paths

The previous chapters described how to define sources, filters and destinations. These components have to be connected together using log statements. The syntax of log statements is described below:

    				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 all the filters is sent to all listed destinations. Log statements are processed in the order they appear in the configuration file.

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

This default behavior can be changed using the `flags()` parameter.

Table 2.4. Log statement flags

Flag | Description
--- | ---
final | This flag means that the processing of log statements ends here. Note that this does not necessarily mean that matching messages will be stored only once, as there can be matching log statements processed prior the current one.
fallback | This flag makes a log statement 'fallback'. Being a 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.
flow-control | Specifies that this log path should be flow controlled, meaning that syslog-ng will stop reading messages from sources feeding destinations through this log statement if the destinations are not able to process the messages at the required speed. If disabled, syslog-ng will drop messages if the destination queues are full. If enabled, syslog-ng will only drop messages if the destination queues/window sizes are improperly sized.

## 6. Options

There are several options that can modify the behavior of syslog-ng. For an exact list of possible options see Section 5, “Options”. Each option may have parameters, similarly to driver specifications. The general syntax is:

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

## Chapter 3. Reference

This chapter documents the drivers and options that can be used in the configuration file.

## 1. Source drivers

The following drivers may be used in source statements, as described in Section 1, “Sources”. The option `log_msg_size()` is available in each source: it specifies the maximum length of incoming log messages in bytes. If not specified, the value of the global option is used (see Section 5, “Options”).

Some parameters affecting message parsing are common for all sources:

Table 3.1. Common options for source drivers

Name | Type | Default | Description
--- | --- | --- | ---
flags() | set of [no-parse,kernel] | empty set | Specifies log parsing flags. `no-parse` completely disables syslog message parsing and processes the complete line as the message part of a syslog message. Other information (timestamp, host, etc.) is added automatically. This flag is useful for parsing files not complying to the syslog format. `kernel` makes the source default to the `LOG_KERN | LOG_CRIT` priority if not specified otherwise.
log_msg_size() | number | The value specified by the global `log_msg_size()` option, which defaults to `8192`. | Specifies the maximum length of incoming log messages. Uses the value of the global option if not specified.
log_iw_size() | number | 100 | The size of the initial window, this value is used during flow control.
log_fetch_limit() | number | The value specified by the global `log_fetch_limit()` option, which defaults to `10`. | The maximum number of messages fetched from a source during a single poll loop. The destination queues might fill up before flow-control could stop reading if `log_fetch_limit()` is too high.
log_prefix() | string |  | A string prepended to every log message. It can be used to prepend an arbitrary string to any log source, though it is most commonly used for adding `kernel:` to the kernel messages on Linux.
pad_size() | number | 0 | Specifies input padding. Some operating systems (such as HP-UX) pad all 0 messages to block boundary. This option can be used to specify the block size. (HP-UX uses 2048 bytes). Syslog-ng will pad reads from the associated device to the number of bytes set in `pad_size()`. Mostly used on HP-UX where `/dev/log` is a named pipe and every write is padded to 2048 bytes.
follow_freq() | number | -1 | Indicates that the source should be checked periodically instead of being polled. This is useful for files which always indicate readability, even though no new lines were appended. If this value is higher than zero, syslog-ng will not attempt to use `poll()` on the file, but checks whether the file changed every time the `follow_freq()` interval (in seconds) has elapsed.
time_zone() | timezone in the form +/-HH:MM |  | The default timezone for messages read from the source. Applies only if no timezone is specified within the message itself.
optional() | yes or no |  | Instruct syslog-ng to ignore the error if a specific source cannot be initialized. No other attempts to initialize the source will be made until the configuration is reloaded. This option currently applies to the `pipe()`, `unix-dgram`, and `unix-stream` drivers.
keep_timestamp() | yes or no | yes | Specifies whether syslog-ng should accept the timestamp received from the peer. If disabled, the time of reception will be used instead.

### 1.1. internal()

All internally generated messages "come" from this special source. To collect warnings, errors and notices from syslog-ng itself, 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(); };

### 1.2. unix-stream() and unix-dgram()

These two drivers behave similarly: they open the given `AF_UNIX` socket and start listening on it for messages. `unix-stream()` is primarily used on Linux and uses `SOCK_STREAM` semantics (connection oriented, no messages are lost); while `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 have a single required positional argument, specifying the filename of the socket to create, and several optional parameters.

### Note

`syslogd` on Linux originally used `SOCK_STREAM` sockets but this was changed in some distributions to `SOCK_DGRAM` at around 1999. The change was a fix to a possible DoS problem, however, this might not have been a proper solution. On Linux you can choose to use whichever driver you like as syslog clients automatically detect the socket type being used.

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

The following options can be specified for these divers:

Table 3.2. Available options for unix-stream() and unix-dgram()

Name | Type | Description | Default
--- | --- | --- | ---
owner() | string | Set the uid of the socket. | root
group() | string | Set the gid of the socket. | root
perm() | number | Set the permission mask. For octal numbers prefix the number with '0', e.g.: use 0755 for rwxr-xr-x. | 0666
keep-alive() | yes or no | Selects whether to keep connections open when syslog-ng is restarted; can be used only with `unix-stream()`. | yes
max-connections() | number | Limits the number of simultaneously open connections. Can be used only with `unix-stream()`. | 10
so_broadcast | yes or no | no | This option controls the `SO_BROADCAST` socket option required to make syslog-ng send messages to a broadcast address. See the socket(7) manual page for details.
so_rcvbuf | number | 0 | Specifies the size of the socket receive buffer in bytes.
so_sndbuf | number | 0 | Specifies the size of the socket send buffer in bytes.
so_keepalive | yes or no | 0 | Specifies whether to enable SO_KEEPALIVE socket option, which enabled TCP keep alive messages for instance.

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 BSD
    						source s_dgram { unix-dgram("/var/run/log"); };

### 1.3. tcp(), tcp6(), udp() and udp6()

These drivers enable to receive messages from the network. As the name of the drivers implies, both UDP and TCP can be used to transport messages. The `tcp6()` and `udp6()` use the IPv6 network protocol.

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 at the protocol level to retransmit such lost messages. The syslog protocol traditionally uses UDP.

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 is safer to use TCP, because lost connections can be detected, and no messages get lost, assuming that the TCP connection does not break. When a TCP connection is broken the 'in-transit' messages that were sent by syslog-ng but not yet received on the other side are lost. (Basically these messages are still sitting in the socket buffer of the sending host and syslog-ng has no information about the fate of these messages).

The `tcp()` and `udp()` drivers do not require any 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 only one interface, use the `localip()` parameter as described below.

### Note

The tcp port 514 is reserved for use with rshell, so select a different port if syslog-ng and rshell is used at the same time.

If you specify a multicast bind address to `udp()` and `udp6()`, syslog-ng will automatically join the necessary multicast group. TCP does not support multicasting.

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

The following options are valid for `tcp()`, `tcp6()`, `udp()`, and `udp6()`

Table 3.3. Available options for tcp(), tcp6(), udp(), and udp6()

Name | Type | Description | Default
--- | --- | --- | ---
ip() or localip() | string | The IP address to bind to. Note that this is not the address where messages are accepted from. | 0.0.0.0
port() or localport() | number | The port number to bind to. | 514
keep-alive() | yes or no | Available for `tcp()` only; specifies whether connections should be closed upon the receipt of a SIGHUP signal. | yes
tcp-keep-alive() | yes or no | Obsolete alias for so_keep_alive() | same as the default of so_keep_alive()
max-connections() | number | Specifies the maximum number of simultaneous connections. | 10
so_broadcast | yes or no | no | This option controls the `SO_BROADCAST` socket option required to make syslog-ng send messages to a broadcast address. See the socket(7) manual page for details.
so_rcvbuf | number | 0 | Specifies the size of the socket receive buffer in bytes.
so_sndbuf | number | 0 | Specifies the size of the socket send buffer in bytes.
ip_ttl | number | 0 | Specifies the Time-To-Live value of outgoing packets.
ip_tos | number | 0 | Specifies the Type-of-Service value of outgoing packets.

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(); };

### 1.4. 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 the `file()` driver is needed. Please note that this driver cannot follow a file like tail -f does. To feed a growing logfile into syslog-ng (e.g.: an HTTP `access.log`), use a script like this:

Example 3.4. 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 has only the common source specific options as specified in Table 3.1, “Common options for source drivers”.

    					Declaration:
    					file(filename);

Example 3.5. Using the file() driver

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

### Note

On Linux, the `klogd` daemon can be used in addition to syslog-ng to read kernel messages and forward them to syslog-ng. `klogd` used to preprocess kernel messages to resolve symbols etc., but as this is deprecated by `ksymoops` there is really no point in running both `klogd` and syslog-ng in parallel. Also note that running two processes reading `/proc/kmsg` at the same time might result in dead-locks.

### 1.5. pipe()

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

The pipe driver has a single required parameter, specifying the filename of the pipe to open. It has only the common source specific options as specified in Table 3.1, “Common options for source drivers”.

Pipe is very similar to the `file()` driver, but there are a few differences, for example `pipe()` opens its argument in read-write mode, therefore it is not recommended to be used on special files like `/proc/kmsg`.

### Warning

It is not recommended to use `pipe()` on anything else than real pipes.

    					Declaration:
    					pipe(filename);

### Note

You have to create this pipe using mkfifo(1).

Example 3.6. Using the pipe() driver

    						source s_pipe { pipe("/dev/log" pad_size(2048)); };

### 1.6. sun-streams() driver

Solaris uses its `STREAMS` framework to send messages to the `syslogd` process. syslog-ng has to be compiled with this driver enabled for `sun-streams()` to be usable (see ./configure --help).

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

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

Example 3.7. Using the sun-streams() driver

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

Table 3.4. Available options for sun-streams

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

## 2. Destination drivers

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

Some of the parameters affecting message formatting and sending are common for all destinations.

Table 3.5. Common options for destination drivers

Name | Type | Default | Description
--- | --- | --- | ---
flags() |  | empty set |
log_fifo_size() | number | Use global setting. | The number of entries in the output fifo.
fsync() | yes or no | no | Forces an `fsync()` call on the destination fd after each write. Note: this may seriously degrade performance.
sync_freq() | number | Use global setting. | This setting is an obsolete alias of the `flush_lines()` option.
flush_lines() | number | Use global setting. | Specifies how many lines are flushed to a destination at a time. Syslog-ng waits for this number of lines to accumulate and sends them off in a single batch. Setting this number high increases throughput as fully filled frames are sent to the network, but also increases message latency. The latency can be limited by the use of the `flush_timeout` option.
flush_timeout() | time in milliseconds | Use global setting. | Specifies the time syslog-ng waits for lines to accumulate in its output buffer. See the `flush_lines` option for more information.
template() | string | A format conforming to the default logfile format. | Specifies a template defining the logformat to be used in the destination. Macros are described in Section 4, “Macros”. Please note that for network destinations it might not be appropriate to change the template as it changes the on-wire format of the syslog protocol which might not be tolerated by stock syslog receivers (like `syslogd` or syslog-ng itself). For network destinations make sure the receiver can cope with the custom format defined.
template_escape() | yes or no | yes | Turns on escaping `'` and `"` in templated output files. This is useful for generating SQL statements and quoting string contents so that parts of the log message are not interpreted as commands to the SQL server.
ts_format() | rfc3164, bsd, rfc3339, iso | rfc3164 | Override the global timestamp format (set in the global `ts_format()` parameter) for the specific destination.
frac_digits() | number | 0 | syslog-ng can store fractions of a second in the timestamps. `frac_digits()` specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the time the message was received.

### Note

The `usertty` destination does not support templates.

### 2.1. file()

The file driver is one of the most important destination drivers in syslog-ng. It allows to output messages to the specified file, or to a set of files.

The destination filename may include macros which get expanded when the message is written, thus a simple `file()` driver may crete several files. For more information on available macros see Section 4, “Macros”.

If the expanded filename refers to a directory which does not 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 is closed, and its state is freed.

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

The most suspicious macro is `$PROGRAM`, where the number of possible variations is quite high, so in untrusted environments `$PROGRAM` should not be used.

Apart from the common destination options described in Table 3.5, “Common options for destination drivers” the `file()` destination has the following options:

Table 3.6. Available options for file()

Name | Type | Default | Description
--- | --- | --- | ---
owner() | string | Set the owner of the created file to the one specified. | root
group() | string | Set the group of the created file to the one specified. | root
perm() | number | The permission mask of the file if it is created by syslog-ng. For octal numbers prefix the number with '0', e.g.: use 0755 for rwxr-xr-x. | 0600
create_dirs() | yes or no | Enable creating non-existing directories. | no
dir_perm() | number | The permission mask of directories created by syslog-ng. Log directories are only created if a file after macro expansion refers to a non-existing directory, and directory creation is enabled (see the `create_dirs()` option below). For octal numbers prefix the number with '0', e.g.: use 0755 for rwxr-xr-x. | 0600
dir_owner() | string | The owner of directories created by syslog-ng. | root
dir_group() | string | The group of directories created by syslog-ng. | root
overwrite_if_older() | number | If set to a value higher than 0, before reopening a file, syslog-ng checks whether the destination file is older than the specified amount of time (specified in seconds). If so, it removes the existing file and the line to be written is the first line of a new file having the same name. In combination with e.g.: the `$WEEKDAY` macro, this can be used for simple log rotation, in case not all history has to be kept. | Never remove existing files; use append instead ( = 0).
remove_if_older() | number | Obsolete alias for overwrite_if_older() | Same as overwrite_if_older()

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)
    						);
    						};

### 2.2. 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 have to create this pipe using mkfifo(1).

Apart from the common destination options described in Table 3.5, “Common options for destination drivers” the `pipe()` destination has the following options:

Table 3.7. Available options for pipe()

Name | Type | Description | Default
--- | --- | --- | ---
owner() | string | Set the owner of the pipe to the one specified. | root
group() | string | Set the group of the pipe to the one specified. | root
perm() | number | The permission mask of the pipe. For octal numbers prefix the number with '0', e.g.: use 0755 for rwxr-xr-x. | 0600
template() | string | Specifies a template which defines the logformat to be used. Possible macros are the same as for the `file()` destination. | A format conforming to the default logfile format.
template_escape() | yes or no | Turns on escaping ' and " in templated output files. This is useful for generating SQL statements and quoting string contents so that parts of the log message are not interpreted as commands to the SQL server. | yes

Example 3.10. Using the pipe() driver

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

### 2.3. 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]);

Apart from the common destination options described in Table 3.5, “Common options for destination drivers” the `unix-stream()` and `unix-dgram()` destinations has the following options:

Table 3.8. Available options for unix-stream() and unix-dgram()

Name | Type | Default | Description
--- | --- | --- | ---
so_broadcast | yes or no | no | This option controls the `SO_BROADCAST` socket option required to make syslog-ng send messages to a broadcast address. See the socket(7) manual page for details.
so_rcvbuf | number | 0 | Specifies the size of the socket receive buffer in bytes.
so_sndbuf | number | 0 | Specifies the size of the socket send buffer in bytes.

Example 3.11. Using the unix-stream() driver

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

### 2.4. udp(), udp6(), tcp() and tcp6()

This driver sends messages to another host on the local intranet or internet using either UDP or TCP protocol. The `tcp6()` and `udp6()` drivers use the IPv6 network 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.

`udp()` and `udp6()` automatically send multicast packets if a multicast destination address is specified. `tcp()` and `tcp6()` do not support multicasting.

    					Declaration:
    					tcp(host [options]);
    					udp(host [options]);
    					tcp6(host [options]);
    					udp6(host [options]);

Apart from the common destination options described in Table 3.5, “Common options for destination drivers” these destinations have the following options:

Table 3.9. Available options for udp(), udp6(), tcp() and tcp6()

Name | Type | Default | Description
--- | --- | --- | ---
localip() | string | The IP address to bind to before connecting to target. | 0.0.0.0
localport() | number | The port number to bind to. | 0
port() or destport() | number | The port number to connect to. | 514
spoof_source | yes or no | 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 syslog-ng then forward messages to your 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. | no
so_broadcast | yes or no | no | This option controls the `SO_BROADCAST` socket option required to make syslog-ng send messages to a broadcast address. See the socket(7) manual page for details.
so_rcvbuf | number | 0 | Specifies the size of the socket receive buffer in bytes.
so_sndbuf | number | 0 | Specifies the size of the socket send buffer in bytes.
ip_ttl | number | 0 | Specifies the Time-To-Live value of outgoing packets.
ip_tos | number | 0 | Specifies the Type-of-Service value of outgoing packets.

Example 3.12. Using the tcp() driver

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

### 2.5. 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.

    					Declaration:
    					usertty(username);

`usertty()` has only the common destination options described in Table 3.5, “Common options for destination drivers”.

### Note

The `usertty()` destination does not support templates.

Example 3.13. Using the usertty() driver

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

### 2.6. program()

This driver executes the specified program with the specified arguments and sends messages to the standard input (`stdin`) of the child.

The `program()` driver has a single required parameter, specifying a program name to start. 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

Syslog-ng 1.6 executed the program once at startup, and kept it running until SIGHUP or exit. The reason was to prevent starting up a large number of programs for messages, which would have enabled an easy DoS attack.

Syslog-ng 2.0 on the other hand restarts the program if it exits, mainly for reliability reasons. However it is not recommended to launch programs for single messages as that might easily cause a DoS for the system.

The program destination supports all common destination options described in Table 3.5, “Common options for destination drivers”. The default message format that is sent to the program matches the BSD syslog protocol, e.g. it includes the priority value in addition to the format used in logfiles.

Example 3.14. Using the program() destination driver

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

## 3. Filter functions

The following functions may be used in the filter statement, as described in Section 2, “Filters”.

Table 3.10. Available filter functions in syslog-ng

Name | Synopsis | Description
--- | --- | ---
facility | facility(facility[,facility]) | Match messages having one of the listed facility code. An alternate syntax permits the use an arbitrary facility codes.
facility | facility(<numeric facility code>) | An alternate syntax for `facility` permitting the use of an arbitrary facility code. Facility codes 0-23 are predefined and can be referenced by their usual name. Facility codes above 24 are not defined but can be used by this alternate syntax.
level() or priority() | level(pri[,pri1..pri2[,pri3]]) | Match messages based on priority.
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(filtername) | Call another filter rule and evaluate its value.
netmask() | netmask(ip/mask) | Check the sender's IP address whether it is in the specified IP subnet.

## 4. Macros

Certain parts of syslog-ng (e.g.: destination filenames and message content templates) can refer to one or more macros, which get expanded as a message is processed. The table below summarizes the macros available in syslog-ng.

Macros can be included by prefixing the macro name with a `$` sign, just like in Bourne compatible shells. syslog-ng 2.0 uses a new syntax for braces around macro names: `"$MSG"` and `"${MSG}"` are equivalent.

The macros related to the time of the message (e.g.: `ISODATE`, `HOUR`, etc.) have two further versions each: one with the `S_` and one with the `R_` prefix (e.g.: `S_DATE` and `R_DATE` ). The `S_DATE` macro represents the date found in the log message, i.e. when the message was sent by the original application. `R_DATE` is the date when syslog has received the message. `DATE` equals either `S_DATE` or `R_DATE`, depending on the global option set in the now deprecated `use_time_recvd()` parameter (see Section 5, “Options”).

Table 3.11. Available macros in filename expansion

Name | Description
--- | ---
FACILITY | The name of the facility from where the message originates.
PRIORITY or LEVEL | The priority of the message.
TAG | The priority and facility encoded as a 2 digit hexadecimal number.
PRI | The priority and facility encoded as a 2 or 3 digit decimal number as it is present in syslog messages.
DATE, R_DATE, S_DATE | Date of the message using the BSD-syslog style timestamp format (month/day/hour/minute/second, each expressed in two digits). This is the original syslog time stamp without year information, e.g.: `Jun 13 15:58:00`.
FULLDATE, R_FULLDATE, S_FULLDATE | A nonstandard format for the date of the message using the same format as `DATE`, but including the year as well, e.g.: `2006 Jun 13 15:58:00`.
ISODATE, R_ISODATE, S_ISODATE | Date of the message in the ISO 8601 compatible standard timestamp format (yyyy-mm-ddThh:mm:ss+-ZONE), e.g.: `2006-06-13T15:58:00.123+01:00`. If possible, it is recommended to use `ISODATE` for timestamping. Note that syslog-ng can produce fractions of a second in the timestamp by using the `frac_digits()` global or per-destination option.
STAMP, R_STAMP, S_STAMP | A timestamp formatted according to the `ts_format()` global or per-destination option.
YEAR, R_YEAR, S_YEAR | The year the message was sent.
MONTH, R_MONTH, S_MONTH | The month the message was sent.
DAY, R_DAY, S_DAY | The day the message was sent.
WEEKDAY, R_WEEKDAY, S_WEEKDAY | The 3-letter name of the day of week the message was sent, e.g. `Thu`.
WEEK, R_WEEK, S_WEEK | The week number of the year. (The first Monday in the year marks the first week.)
HOUR, R_HOUR, S_HOUR | The hour of day the message was sent.
MIN, R_MIN, S_MIN | The minute the message was sent.
SEC, R_SEC, S_SEC | The second the message was sent.
UNIXTIME, R_UNIXTIME, S_UNIXTIME | Standard unix timestamp, represented as the number of seconds since `1970-01-01T00:00:00`.
TZOFFSET, R_TZOFFSET, S_TZOFFSET | The time-zone as hour offset from GMT; e.g.: `-07:00`. In syslog-ng 1.6.x this used to be `-0700` but as `ISODATE` requires the colon it was added to `TZOFFSET` as well.
TZ, R_TZ, S_TZ | Equivalent to TZOFFSET, used to mean the time zone name abbreviation in syslog-ng 1.6.x.
HOST | The name of the source host where the message originates from. If the message traverses several hosts and the `chain_hostnames()` option is on (see Section 5, “Options”), the first host in the chain is used.
FULLHOST | The full FQDN of the host name chain (without trimming chained hosts), including the domain name.
HOST_FROM | Name of the host that sent the message to syslog-ng, as resolved by syslog-ng using DNS. If the message traverses several hosts, this is the last host in the chain.
FULLHOST_FROM | FQDN of the host that sent the message to syslog-ng as resolved by syslog-ng using DNS. If the message traverses several hosts, this is the last host in the chain.
SOURCEIP | IP address of the host that sent the message to syslog-ng. (I.e. the IP address of the host in the `FULLHOST_FROM` macro.) Please note that when a message traverses several relays, this macro contains the IP of the last relay.
PROGRAM | The name of the program sending the message.
PID | The PID of the program sending the message.
MSG or MESSAGE | Message contents including the program name and pid.
MSGONLY | Message contents without the program name.

## 5. Options

The following options can be specified in the options statement, as described in Section 6, “Options”.

Table 3.12. List of global options supported in syslog-ng

Name | Accepted values | Default | Description
--- | --- | --- | ---
time_reopen() | number | The time to wait in seconds before a dead connection is reestablished. | 60
time_reap() | number | The time to wait in seconds before an idle destination file is closed. | 60
time_sleep() | number | 0 | The time to wait in milliseconds between each invocation of the `poll()` iteration.
sync() or sync_freq() (DEPRECATED) | number | 0 | Obsolete aliases for `flush_lines()`
mark_freq() | number | 1200 | The number of seconds between two `MARK` lines. `MARK` lines are generated if there was no message traffic to inform the receiver that the connection is still alive.
stats_freq() | number | 600 | The period between two STATS messages in seconds. STATS are log messages sent by syslog-ng, containing statistics about dropped log messages. This parameter is identical to the `stats()` option of syslog-ng 1.6. In syslog-ng 2.0, `stats()` is an alias of `stats_freq()`.
log_fifo_size() | number | 100 | The number of lines fitting to the output queue
chain_hostnames() | yes or no | yes | Enable or disable the chained hostname format.
normalize_hostnames() | yes or no | no | Normalize hostnames, which currently translates to converting them to lower case. (requires 1.9.9)
keep_hostname() | yes or no | no | Enable or disable hostname rewriting.
check_hostname() | yes or no | no | Enable or disable checking whether the hostname contains valid characters.
bad_hostname() | regular expression | no | A regexp containing hostnames which should not be handled as hostnames.
create_dirs() | yes or no | no | Enable or disable directory creation for destination files.
owner() | userid | root | The default owner of output files.
group() | groupid | root | The default group of output files.
perm() | permission value | 0600 | The default permission for output files.
dir_owner() | userid | root | The default owner of newly created directories.
dir_group() | groupid | root | The default group for newly created directories.
dir_perm() | permission value | 0700 | The default permission for newly created directories.
use_time_recvd() (DEPRECATED) | yes or no | no | This option controls how the time related macros are expanded in filename and content templates. If set to yes, then the non-prefixed versions of the time related macros (e.g.: `HOUR` instead of `R_HOUR` and `S_HOUR`) refer to the time when the message was received, otherwise it refers to the timestamp which is in the message. ### Note The timestamps in the messages are generated by the originating host and might not be accurate. ### Note This option is deprecated as many users assumed that it controls the timestamp as it is written to logfiles/destinations, which is not the case. To change how messages are formatted, specify a content-template referring to the appropriate prefixed (`S_` or `R_`) time macro.
ts_format() | rfc3164, bsd, rfc3339, iso | rfc3164 | Specifies the timestamp format used when syslog-ng itself formats a timestamp and nothing else specifies a format (e.g.: `STAMP` macros, internal messages, messages without original timestamps).
use_dns() | yes, no, persist-only | yes | Control DNS usage. "yes" enables DNS queries (with using a cache, see the option dns_cache), "no" disables name resolution completely, "persist-only" uses entries in the DNS cache host file (see option dns_cache_hosts). syslog-ng blocks on DNS queries, so enabling DNS may lead to a Denial of Service attack. To prevent DoS, protect your syslog-ng network endpoint with firewall rules, and make sure that all hosts which may get to syslog-ng are resolvable/or you are using a static IP-name mapping.
dns_cache() | yes or no | yes | Enable or disable DNS cache usage.
dns_cache_size() | number | 1007 | Number of hostnames in the DNS cache.
dns_cache_expire() | number | 3600 | Number of seconds while a successful lookup is cached.
dns_cache_expire_failed() | number | 60 | Number of seconds while a failed lookup is cached.
dns_cache_hosts() | filename | Name of a file in /etc/hosts format that contains static IP->name mappings. By using this option it is possible to resolve names without reliance on DNS. | unset
log_msg_size() | number | 8192 | Maximum length of a message in bytes.
use_fqdn() | yes or no | no | Add Fully Qualified Domain Name instead of short hostname.
gc_idle_threshold() (DEPRECATED) | number | n/a | Has no meaning in syslog-ng 1.9.x and later.
gc_busy_threshold() (DEPRECATED) | number | n/a | Has no meaning in syslog-ng 1.9.x and later.
flush_lines() | number | 0 | Specifies how many lines are flushed to a destination at a time. Syslog-ng waits for this number of lines to accumulate and sends them off in a single batch. Setting this number high increases throughput as fully filled frames are sent to the network, but also increases message latency. The latency can be limited by the use of the `flush_timeout` option.
flush_timeout() | time in milliseconds | 10000 | Specifies the time syslog-ng waits for lines to accumulate in its output buffer. See the `flush_lines()` option for more information.
recv_time_zone() | time offset (e.g.: `+03:00`) | local timezone | Specifies the time zone associated with the incoming messages, if not specified otherwise in the message or in the source driver. See Section 1, “Timezone handling” for details.
send_time_zone() | time offset (e.g.: `+03:00`) | local timezone | Specifies the time zone associated with the messages sent by syslog-ng, if not specified otherwise in the message or in the destination driver. See Section 1, “Timezone handling” for details.
frac_digits() | number | 0 | syslog-ng can store fractions of a second in the timestamps. `frac_digits()` specifies the number of digits stored. The digits storing the fractions are padded by zeros if the original timestamp of the message specifies only seconds. Fractions can always be stored for the received time of the messages.

## 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.

## 1. Setting garbage collector parameters

Syslog-ng 2.0 is a complete reimplementation of syslog-ng 1.6, and does not use the mark and sweep garbage collector at all. The garbage collector parameters (`gc_idle_threshold`, `gc_busy_threshold`) are still accepted but are ignored.

## 2. Setting time_sleep()

When there are a lot of parallel connections to syslog-ng, the amount of time required to prepare for a single poll loop iteration is significant. Since the arrival of every single log message triggers a new iteration, the CPU usage of syslog-ng might increase significantly even if the number of messages received is otherwise low. The solution is to add a fixed latency to message processing to wait some messages to arrive and to process them in blocks. This can be accomplished by setting the `time_sleep()` to a non-zero value. It is not recommended to increase it above 100ms, as that might skew timestamps, slow syslog-ng, and cause messages to be dropped. An alternative solution is to avoid `tcp()` and `unix-stream()` sources and use the DGRAM versions, `udp()` and `unix-dgram()`, respectively.

The value of `fetch_limit()` and `log_fifo_size()` must also be sized accordingly when `time_sleep()` is modified.

## 3. Setting output queue size

syslog-ng always reads its incoming log channels to prevent the running daemons from blocking. This may result in lost messages if the output queue is full, it is therefore important to set the output queue size (termed in number of messages). The size of the output queue can be set either globally, or on a per destination basis.

### Note

This does not apply to syslog-ng 2.0 if the flow-control flag is enabled. See Table 2.4, “Log statement flags” for details.

    			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 the network bandwidth, so if the destination host lives on a noisy network and the logtraffic extends the bandwidth of this network, syslog-ng cannot do anything. However, it will do its best.

## 4. Setting the sync parameter

The `sync` parameter does not exactly do what its name implies. 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 does not write all buffered messages into a single chunk; each distinct message is written with a single `write()` system call.