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syslog-ng Premium Edition 7.0.12 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng The syslog-ng PE quick-start guide The syslog-ng PE configuration file Collecting log messages — sources and source drivers
How sources work default-network-drivers: Receive and parse common syslog messages internal: Collecting internal messages file: Collecting messages from text files wildcard-file: Collecting messages from multiple text files network: Collecting messages using the RFC3164 protocol (network() driver) osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes program: Receiving messages from external applications python: writing server-style Python sources python-fetcher: writing fetcher-style Python sources snmptrap: Read Net-SNMP traps sun-streams: Collecting messages on Sun Solaris syslog: Collecting messages using the IETF syslog protocol (syslog() driver) system: Collecting the system-specific log messages of a platform systemd-journal: Collecting messages from the systemd-journal system log storage systemd-syslog: Collecting systemd messages using a socket tcp, tcp6, udp, udp6: Collecting messages from remote hosts using the BSD syslog protocol unix-stream, unix-dgram: Collecting messages from UNIX domain sockets windowsevent: Collecting Windows event logs
Sending and storing log messages — destinations and destination drivers
elasticsearch: Sending messages directly to Elasticsearch version 1.x elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher file: Storing messages in plain-text files hdfs: Storing messages on the Hadoop Distributed File System (HDFS) http: Posting messages over HTTP kafka: Publishing messages to Apache Kafka logstore: Storing messages in encrypted files mongodb: Storing messages in a MongoDB database network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) pipe: Sending messages to named pipes program: Sending messages to external applications python: writing custom Python destinations smtp: Generating SMTP messages (e-mail) from logs splunk-hec: Sending messages to Splunk HTTP Event Collector sql: Storing messages in an SQL database syslog: Sending messages to a remote logserver using the IETF-syslog protocol syslog-ng: Forwarding messages and tags to another syslog-ng node tcp, tcp6, udp, udp6: Sending messages to a remote log server using the legacy BSD-syslog protocol (tcp(), udp() drivers) unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal — usertty() destination Client-side failover
Routing messages: log paths, flags, and filters Global options of syslog-ng PE TLS-encrypted message transfer Advanced Log Transfer Protocol Reliability and minimizing the loss of log messages Manipulating messages parser: Parse and segment structured messages Processing message content with a pattern database Correlating log messages Enriching log messages with external data Monitoring statistics and metrics of syslog-ng Multithreading and scaling in syslog-ng PE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages About us

snmptrap: Read Net-SNMP traps

Using the snmptrap() source, you can read and parse the SNMP traps of the Net-SNMP's snmptrapd application. syslog-ng PE can read these traps from a log file, and extract their content into name-value pairs, making it easy to forward them as a structured log message (for example, in JSON format). The syslog-ng PE application automatically adds the .snmp. prefix to the name of the fields the extracted from the message.

The snmptrap() source is available in syslog-ng PE version 7.0.3 and later.

  • The snmptrap() source has only the options listed in snmptrap() source options. Other options commonly available in other source drivers are not supported.

  • In addition to traps, the log of snmptrapd may contain other messages (for example, daemon start/stop information, debug logs) as well. Currently syslog-ng PE discards these messages.

  • Because of a bug, snmptrapd does not escape String values in the VarBindList if it can resolve an OID to a symbolic name. As a result, syslog-ng PE cannot process traps that contain the = in the value of the string. To overcome this problem, disable resolving OIDs in snmptrapd.

  • The colon (:) character is commonly used in SNMP traps. However, this character cannot be used in the name of syslog-ng PE macros (name-value pairs). Therefore, the syslog-ng PE application automatically replaces all consecutive : characters with a single underscore (_) character. For example, you can reference the value of the NET-SNMP-EXAMPLES-MIB::netSnmpExampleString key using the ${NET-SNMP-EXAMPLES-MIB_netSnmpExampleString} macro.

    Note that this affects only name-value pairs (macros). The generated message always contains the original name of the key.

  • Configure snmptrapd to log into a file.

  • If you use SMIv1 traps, include the following format string in the configuration file of snmptrapd:

    format1 %.4y-%.2m-%.2l %.2h:%.2j:%.2k %B [%b]: %N\n\t%W Trap (%q) Uptime: %#T\n%v\n
  • If you use SMIv2 traps, use the default format. The snmptrap() source of syslog-ng PE expects this default format:

    format2 %.4y-%.2m-%.2l %.2h:%.2j:%.2k %B [%b]:\n%v\n
  • Beacause of an snmptrapd bug, if you specify the filename in the configuration file with logOption, you must also specify another output as a command line argument (-Lf, -Ls). Otherwise, snmptrapd will not apply the the trap format.

To use the snmptrap() driver, the scl.conf file must be included in your syslog-ng PE configuration:

@include "scl.conf"
Example: Using the snmptrap() driver

A sample snmptrapd configuration:

authCommunity log,execute,net public
format1 %.4y-%.2m-%.2l %.2h:%.2j:%.2k %B [%b]: %N\n\t%W Trap (%q) Uptime: %#T\n%v\n
outputOption s

Starting snmptrapd: snmptrapd -A -Lf /var/log/snmptrapd.log

Sending a sample V2 trap message: snmptrap -v2c -c public 666 NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification netSnmpExampleHeartbeatRate i 60 netSnmpExampleString s "string". From this trap, syslog-ng PE receives the following input:

2017-05-23 15:29:40 localhost [UDP: []:59993->[]:162]:
SNMPv2-SMI::mib- = Timeticks: (666) 0:00:06.66   SNMPv2-SMI::snmpModules. = OID: NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification     NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatRate = INTEGER: 60        NET-SNMP-EXAMPLES-MIB::netSnmpExampleString = STRING: string

The following syslog-ng PE configuration sample uses the default settings of the driver, reading SNMP traps from the /var/log/snmptrapd.log file, and writes the log messages generated from the traps into a file.

@include "scl.conf"
log {
    source {
    destination {

From the trap, syslog-ng PE writes the following into the log file:

May 23 15:29:40 myhostname snmptrapd: hostname='localhost', transport_info='UDP: []:59993->[]:162', SNMPv2-SMI::mib-'(666) 0:00:06.66', SNMPv2-SMI::snmpModules.'NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatNotification', NET-SNMP-EXAMPLES-MIB::netSnmpExampleHeartbeatRate='60', NET-SNMP-EXAMPLES-MIB::netSnmpExampleString='string'

Using the same input trap, the following configuration example formats the SNMP traps as JSON messages.

@include "scl.conf"
log {
    source {

    destination {
            template("$(format-json --scope dot-nv-pairs)\n")

The previous trap formatted as JSON:

      "transport_info":"UDP: []:59993->[]:162",
               "0":"(666) 0:00:06.66"

snmptrap() source options

The snmptrap() driver has the following options. Only the filename() option is required, the others are optional.

Type: path

Description: The log file of snmptrapd. The syslog-ng PE application reads the traps from this file.

In addition to traps, the log of snmptrapd may contain other messages (for example, daemon start/stop information, debug logs) as well. Currently syslog-ng PE discards these messages.

Type: string

Description:If you receive the following error message during syslog-ng PE startup, set the persist-name() option of the duplicate drivers:

Error checking the uniqueness of the persist names, please override it with persist-name option. Shutting down.

This error happens if you use identical drivers in multiple sources, for example, if you configure two file sources to read from the same file. In this case, set the persist-name() of the drivers to a custom string, for example, persist-name("example-persist-name1").

Synopsis: prefix()

Description: Insert a prefix before the name part of the parsed name-value pairs to help further processing. For example:

  • To insert the my-parsed-data. prefix, use the prefix(my-parsed-data.) option.

  • To refer to a particular data that has a prefix, use the prefix in the name of the macro, for example, ${} .

  • If you forward the parsed messages using the IETF-syslog protocol, you can insert all the parsed data into the SDATA part of the message using the prefix( option.

Names starting with a dot (for example, .example) are reserved for use by syslog-ng PE. If you use such a macro name as the name of a parsed value, it will attempt to replace the original value of the macro (note that only soft macros can be overwritten, see Hard vs. soft macros for details). To avoid such problems, use a prefix when naming the parsed values, for example, prefix(my-parsed-data.)

Default value: .snmp. option.

Type: yes|no
Default: yes

Description: The snmptrap() source automatically parses the traps into name-value pairs, so you can handle the content of the trap as a structured message. Consequently, you might not even need the ${MESSAGE} part of the log message. If set-message-macro() is set to no, syslog-ng PE leaves the ${MESSAGE} part empty. If set-message-macro() is set to yes, syslog-ng PE generates a regular log message from the trap.

sun-streams: Collecting messages on Sun Solaris

Solaris uses its STREAMS framework to send messages to the syslogd process. Solaris 2.5.1 and above uses an IPC called door in addition to STREAMS, to confirm the delivery of a message. The syslog-ng application supports the IPC mechanism via the door() option (see below).


The sun-streams() driver must be enabled when the syslog-ng application is compiled (see ./configure --help).

The sun-streams() driver has a single required argument specifying the STREAMS device to open, and the door() option. For the list of available optional parameters, see sun-streams() source options.


Starting with version 7.0.7, the syslog-ng PE system() driver automatically extracts the msgid from the message (if available), and stores it in the .solaris.msgid macro. To extract the msgid from the message without using the system()driver, use the extract-solaris-msgid() parser.

sun-streams(<name_of_the_streams_device> door(<filename_of_the_door>));
Example: Using the sun-streams() driver
source s_stream {
    sun-streams("/dev/log" door("/etc/.syslog_door"));

sun-streams() source options

The sun-streams() driver has the following options.

Type: string
Default: none

Description: Specifies the filename of a door to open, needed on Solaris above 2.5.1.

Type: assume-utf8, empty-lines, expect-hostname, kernel, no-hostname, no-multi-line, no-parse, sanitize-utf8, store-legacy-msghdr, store-raw-message, syslog-protocol, validate-utf8
Default: empty set

Description: Specifies the log parsing options of the source.

  • assume-utf8: The assume-utf8 flag assumes that the incoming messages are UTF-8 encoded, but does not verify the encoding. If you explicitly want to validate the UTF-8 encoding of the incoming message, use the validate-utf8 flag.

  • empty-lines: Use the empty-lines flag to keep the empty lines of the messages. By default, syslog-ng PE removes empty lines automatically.

  • expect-hostname: If the expect-hostname flag is enabled, syslog-ng PE will assume that the log message contains a hostname and parse the message accordingly. This is the default behavior for TCP sources. Note that pipe sources use the no-hostname flag by default.

  • kernel: The kernel flag makes the source default to the LOG_KERN | LOG_NOTICE priority if not specified otherwise.

  • no-hostname: Enable the no-hostname flag if the log message does not include the hostname of the sender host. That way syslog-ng PE assumes that the first part of the message header is ${PROGRAM} instead of ${HOST}. For example:

    source s_dell {
  • no-multi-line: The no-multi-line flag disables line-breaking in the messages: the entire message is converted to a single line. Note that this happens only if the underlying transport method actually supports multi-line messages. Currently the file() and pipe() drivers support multi-line messages.

  • no-parse: By default, syslog-ng PE parses incoming messages as syslog messages. The no-parse flag completely disables syslog message parsing and processes the complete line as the message part of a syslog message. The syslog-ng PE application will generate a new syslog header (timestamp, host, and so on) automatically and put the entire incoming message into the MESSAGE part of the syslog message (available using the ${MESSAGE} macro). This flag is useful for parsing messages not complying to the syslog format.

    If you are using the flags(no-parse) option, then syslog message parsing is completely disabled, and the entire incoming message is treated as the ${MESSAGE} part of a syslog message. In this case, syslog-ng PE generates a new syslog header (timestamp, host, and so on) automatically. Note that since flags(no-parse) disables message parsing, it interferes with other flags, for example, disables flags(no-multi-line).

  • dont-store-legacy-msghdr: By default, syslog-ng stores the original incoming header of the log message. This is useful if the original format of a non-syslog-compliant message must be retained (syslog-ng automatically corrects minor header errors, for example, adds a whitespace before msg in the following message: Jan 22 10:06:11 host program:msg). If you do not want to store the original header of the message, enable the dont-store-legacy-msghdr flag.

  • sanitize-utf8: When using the sanitize-utf8 flag, syslog-ng PE converts non-UTF-8 input to an escaped form, which is valid UTF-8.

  • store-raw-message: Save the original message as received from the client in the ${RAWMSG} macro. You can forward this raw message in its original form to another syslog-ng node using the syslog-ng() destination, or to a SIEM system, ensuring that the SIEM can process it. Available only in 7.0.9 and later.

  • syslog-protocol: The syslog-protocol flag specifies that incoming messages are expected to be formatted according to the new IETF syslog protocol standard (RFC5424), but without the frame header. Note that this flag is not needed for the syslog driver, which handles only messages that have a frame header.

  • validate-utf8: The validate-utf8 flag enables encoding-verification for messages formatted according to the new IETF syslog standard (for details, see IETF-syslog messages). If theBOM1character is missing, but the message is otherwise UTF-8 compliant, syslog-ng automatically adds the BOM character to the message.

Type: number
Default: 1

Description: Indicates that the source should be checked periodically. 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. Floating-point numbers (for example 1.5) can be used as well.

Type: yes or no
Default: yes

Description: Specifies whether syslog-ng should accept the timestamp received from the sending application or client. If disabled, the time of reception will be used instead. This option can be specified globally, and per-source as well. The local setting of the source overrides the global option if available.


To use the S_ macros, the keep-timestamp() option must be enabled (this is the default behavior of syslog-ng PE).

Type: number
Default: 10

Description: 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.

Type: number
Default: 100

Description: The size of the initial window, this value is used during flow control. For details on flow control, see Managing incoming and outgoing messages with flow-control.

Type: number (bytes)
Default: Use the global log-msg-size() option, which defaults to 65536.

Description: Maximum length of a message in bytes. This length includes the entire message (the data structure and individual fields). The maximal value that can be set is 268435456 bytes (256MB). For messages using the IETF-syslog message format (RFC5424), the maximal size of the value of an SDATA field is 64kB.

In most cases, it is not recommended to set log-msg-size() higher than 10 MiB.

For details on how encoding affects the size of the message, see Message size and encoding.

Uses the value of the global option if not specified.

log-prefix() (DEPRECATED)
Type: string

Description: A string added to the beginning of every log message. It can be used to add an arbitrary string to any log source, though it is most commonly used for adding kernel: to the kernel messages on Linux. NOTE: This option is deprecated. Use program-override() instead.

Type: yes or no

Description: 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.

Type: number
Default: 0

Description: Specifies input padding. Some operating systems (such as HP-UX) pad all messages to block boundary. This option can be used to specify the block size. The syslog-ng PE application 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. If pad-size() was given and the incoming message does not fit into pad-size(), syslog-ng will not read anymore from this pipe and displays the following error message:

Padding was set, and couldn't read enough bytes
Type: string

Description: Replaces the ${PROGRAM} part of the message with the parameter string. For example, to mark every message coming from the kernel, include the program-override("kernel") option in the source containing /proc/kmsg.

Type: string

Description: Label the messages received from the source with custom tags. Tags must be unique, and enclosed between double quotes. When adding multiple tags, separate them with comma, for example tags("dmz", "router"). This option is available only in syslog-ng 3.1 and later.

Type: name of the timezone, or the timezone offset

Description: The default timezone for messages read from the source. Applies only if no timezone is specified within the message itself.

The timezone can be specified as using the name of the (for example time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format (for example +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.

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