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syslog-ng Premium Edition 7.0.17 - 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 linux-audit: Collecting messages from Linux audit logs network: Collecting messages using the RFC3164 protocol (network() driver) office365: Fetching logs from Office 365 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
elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher (DEPRECATED) elasticsearch-http: Sending messages to Elasticsearch HTTP Event Collector 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 (email) from logs splunk-hec: Sending messages to Splunk HTTP Event Collector sql: Storing messages in an SQL database stackdriver: Sending logs to the Google Stackdriver cloud syslog: Sending messages to a remote logserver using the IETF-syslog protocol syslog-ng(): Forward logs 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

monitoring() source options

The monitoring() driver has the following options. Only the query() option is required, other options are optional.

Type: boolean
Default: no

Description: Reset the counters after reading. Note that if a destination is not available, syslog-ng PE will not reset its counter even if clear-on-read() is set to yes.

If you use multiple monitoring source, and you use the clear-on-read() parameter, make sure to adjust the queries appropriately. Overlapping queries that read and reset the same counters result in incorrect statistics.

Type: integer
Default: 600 [seconds]

Description: Specifies how often does syslog-ng PE execute the query and send a statistics message.

Type: string
Default: N/A

Description: Specifies how the message containing the queried statistics is formatted. You can use macros and template functions in the format string. For example, you can format the message as a JSON object:

source s_monitor{ monitoring(
    message-template('$(format-json --scope nv_pairs)')

Note that here you can only format the payload of the message (that is the, ${MESSAGE} part). You can format the headers or other parts of the outgoing message in the destination driver.

Type: string
Default: N/A

Description: Specifies which statistical counters will be included in the messages. Note that the list of available counters depends on your syslog-ng PE configuration (mainly the configured sources and destinations) and on the stats-level() global option. The * string includes every available counters. The syntax of the query option is identical to the syslog-ng-ctl query get <query> command.

source s_monitor{ monitoring(

For example, the "destination*" query lists the configured destinations, and the metrics related to each destination. An example output:,elasticsearch-syslog-ng-test,t7cde889529c034aea9ec_micek).stats.dropped: 0,elasticsearch-syslog-ng-test,t7cde889529c034aea9ec_micek).stats.processed: 0,elasticsearch-syslog-ng-test,t7cde889529c034aea9ec_micek).stats.stored: 0
destination.d_elastic.stats.processed: 0

The monitoring-welf() source

This source is actually preconfigured monitoring() source that generates statistics messages in WELF format. Starting with syslog-ng PE version 7.0.2, syslog-ng PE uses this driver for new installations to generate statistics. By default, a message is sent every 10 minutes (600 seconds).

@version: 7.0
@include 'scl.conf'
options {
source s_monitoring_welf {
    monitoring-welf(freq(10) query('*'));
destination d_file {
log {

The output is similar to the following:

Apr 3 14:03:26 example-host syslog-ng[12363]: PID=12363 PROGRAM=syslog-ng center.queued.processed=0 center.received.processed=0 destination.d_file.processed=0 global.msg_clones.processed=0 global.payload_reallocs.processed=2 global.sdata_updates.processed=0 source.s_monitoring_welf.processed=0 src.facility.0.processed=0 src.facility.1.processed=0 src.facility.10.processed=0 src.facility.11.processed=0 src.facility.12.processed=0 src.facility.13.processed=0 src.facility.14.processed=0 src.facility.15.processed=0 src.facility.16.processed=0 src.facility.17.processed=0 src.facility.18.processed=0 src.facility.19.processed=0 src.facility.2.processed=0 src.facility.20.processed=0 src.facility.21.processed=0 src.facility.22.processed=0 src.facility.23.processed=0 src.facility.3.processed=0 src.facility.4.processed=0 src.facility.5.processed=0 src.facility.6.processed=0 src.facility.7.processed=0 src.facility.8.processed=0 src.facility.9.processed=0 src.facility.other.processed=0 src.monitoring.s_monitoring_welf#0.processed=0 src.monitoring.s_monitoring_welf#0.stamp=0 src.severity.0.processed=0 src.severity.1.processed=0 src.severity.2.processed=0 src.severity.3.processed=0 src.severity.4.processed=0 src.severity.5.processed=0 src.severity.6.processed=0 src.severity.7.processed=0\x0a'

Multithreading and scaling in syslog-ng PE

Starting with version 4 F1, syslog-ng PE can process sources and destinations in multithreaded mode to scale to multiple CPUs or cores for increased performance. Starting with version 5 F4, this multithreaded mode is the default.

Multithreading concepts of syslog-ng PE

This section is a brief overview on how syslog-ng PE works in multithreaded mode. It is mainly for illustration purposes: the concept has been somewhat simplified and may not completely match reality.


The way syslog-ng PE uses multithreading may change in future releases. The current documentation applies to version 7.

syslog-ng PE always uses multiple threads:

  • A main thread that is always running

  • A number of worker threads that process the messages. You can influence the behavior of worker threads using the threaded() option and the --worker-threads command-line option.

  • Some other, special threads for internal functionalities. For example, certain destinations run in a separate thread, independently of the multithreading (threaded()) and --worker-threads settings of syslog-ng PE.

The maximum number of worker threads syslog-ng PE uses is the number of CPUs or cores in the host running syslog-ng PE (up to 64). You can limit this value using the --worker-threads command-line option that sets the maximum total number of threads syslog-ng PE can use, including the main syslog-ng PE thread. However, the --worker-threads option does not affect the supervisor of syslog-ng PE. The supervisor is a separate process (see The syslog-ng manual page), but certain operating systems might display it as a thread. In addition, certain destinations always run in a separate thread, independently of the multithreading (threaded()) and --worker-threads settings of syslog-ng PE.

When an event requiring a new thread occurs (for example, syslog-ng PE receives new messages, or a destination becomes available), syslog-ng PE tries to start a new thread. If there are no free threads, the task waits until a thread finishes its task and becomes available. There are two types of worker threads:

  • Reader threads read messages from a source (as many as possible, but limited by the log-fetch-limit() and log-iw-size() options. The thread then processes these messages, that is, performs filtering, rewriting and other tasks as necessary, and puts the log message into the queue of the destination. If the destination does not have a queue (for example, usertty), the reader thread sends the message to the destination, without the interaction of a separate writer thread.

  • Writer threads take the messages from the queue of the destination and send them to the destination, that is, write the messages into a file, or send them to the syslog server over the network. The writer thread starts to process messages from the queue only if the destination is writable, and there are enough messages in the queue, as set in the flush-lines() and the flush-timeout() options. Writer threads stop processing messages when the destination becomes unavailable, or there are no more messages in the queue.

Sources and destinations affected by multithreading

The following list describes which sources and destinations can use multiple threads. Changing the --worker-threads command-line option changes the number of threads available to these sources and destinations.

  • The tcp and syslog(tcp) sources can process independent connections in separate threads. The number of independent connections is limited by the max-connections() option of the source. Separate sources are processed by separate thread, for example, if you have two separate tcp sources defined that receive messages on different IP addresses or port, syslog-ng PE will use separate threads for these sources even if they both have only a single active connection.

  • The udp, file, and pipe sources use a single thread for every source statement.

  • The tcp, syslog, and pipe destinations use a single thread for every destination.

  • The file destination uses a single thread for writing the destination file, but may use a separate thread for each destination file if the filename includes macros.

Sources and destinations not affected by multithreading

The following list describes sources and destinations that use a separate thread even if you disable multithreading in syslog-ng PE, in addition to the limit set in the --worker-threads command-line option.

  • The logstore destination uses separate threads for writing the messages from the journal to the logstore files, and also for timestamping. These threads are independent from the setting of the --worker-threads command-line option.

  • Every sql destination uses its own thread. These threads are independent from the setting of the --worker-threads command-line option.

  • The java destinations use one thread, even if there are multiple Java-based destinations configured. This thread is independent from the setting of the --worker-threads command-line option.

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