syslog-ng Open Source Edition 3.38 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng The syslog-ng OSE quick-start guide The syslog-ng OSE configuration file source: Read, receive, and collect log messages
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 kubernetes: Collecting and parsing the Kubernetes CRI (Container Runtime Interface) format linux-audit: Collecting messages from Linux audit logs mqtt: receiving messages from an MQTT broker network: Collecting messages using the RFC3164 protocol (network() driver) nodejs: Receiving JSON messages from nodejs applications mbox: Converting local email messages to log messages osquery: Collect and parse osquery result logs pipe: Collecting messages from named pipes pacct: Collecting process accounting logs on Linux 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— OBSOLETE unix-stream, unix-dgram: Collecting messages from UNIX domain sockets stdin: Collecting messages from the standard input stream
destination: Forward, send, and store log messages
amqp: Publishing messages using AMQP collectd: sending metrics to collectd discord: Sending alerts and notifications to Discord elasticsearch2: Sending messages directly to Elasticsearch version 2.0 or higher (DEPRECATED) elasticsearch-http: Sending messages to Elasticsearch HTTP Bulk API file: Storing messages in plain-text files graphite: Sending metrics to Graphite Sending logs to Graylog hdfs: Storing messages on the Hadoop Distributed File System (HDFS) Posting messages over HTTP http: Posting messages over HTTP without Java kafka: Publishing messages to Apache Kafka (Java implementation) kafka-c(): Publishing messages to Apache Kafka using the librdkafka client (C implementation) loggly: Using Loggly logmatic: Using mongodb(): Storing messages in a MongoDB database mqtt() destination: sending messages from a local network to an MQTT broker network: Sending messages to a remote log server using the RFC3164 protocol (network() driver) osquery: Sending log messages to osquery's syslog table pipe: Sending messages to named pipes program: Sending messages to external applications pseudofile() python: writing custom Python destinations redis: Storing name-value pairs in Redis riemann: Monitoring your data with Riemann slack: Sending alerts and notifications to a Slack channel smtp: Generating SMTP messages (email) from logs snmp: Sending SNMP traps Splunk: Sending log messages to Splunk sql: Storing messages in an SQL database stomp: Publishing messages using STOMP Sumo Logic destinations: sumologic-http() and sumologic-syslog() 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) Telegram: Sending messages to Telegram unix-stream, unix-dgram: Sending messages to UNIX domain sockets usertty: Sending messages to a user terminal: usertty() destination Write your own custom destination in Java or Python Client-side failover
log: Filter and route log messages using log paths, flags, and filters Global options of syslog-ng OSE TLS-encrypted message transfer template and rewrite: Format, modify, and manipulate log messages parser: Parse and segment structured messages
Parsing syslog messages Parsing messages with comma-separated and similar values Parsing key=value pairs JSON parser XML parser Parsing dates and timestamps Python parser Parsing tags Apache access log parser Linux audit parser Cisco parser Parsing enterprise-wide message model (EWMM) messages iptables parser Netskope parser panos-parser(): parsing PAN-OS log messages Sudo parser MariaDB parser Websense parser Fortigate parser Check Point Log Exporter parser Regular expression (regexp) parser db-parser: Process message content with a pattern database (patterndb)
Correlating log messages Enriching log messages with external data Statistics of syslog-ng Multithreading and scaling in syslog-ng OSE Troubleshooting syslog-ng Best practices and examples The syslog-ng manual pages Creative Commons Attribution Non-commercial No Derivatives (by-nc-nd) License The syslog-ng Open Source Edition Documentation License Glossary

Metrics and counters of syslog-ng OSE

You can list all active metrics on your syslog-ng OSE host using the following command (this lists the metrics, without their current values): syslog-ng-ctl query list "*"

To list the metrics and their values, use the following command: syslog-ng-ctl query get "*"

The displayed metrics have the following structure.

  1. The type of the object (for example, dst.file, tag, src.facility)

  2. The ID of the object used in the syslog-ng configuration file, for example, d_internal or source.src_tcp. The #0 part means that this is the first destination in the destination group.

  3. The instance ID (destination) of the object, for example, the filename of a file destination, or the name of the application for a program source or destination.

  4. The status of the object. One of the following:

    • a - active. At the time of quering the statistics, the source or the destination was still alive (it continuously received statistical data).

    • d - dynamic. Such objects may not be continuously available, for example, like statistics based on the sender's hostname. These counters only appear above a certain value of stats-level() global option:

      • host: source host, from stats-level(2)

      • program: program, from stats-level(3)

      • sender: sender host, from stats-level(3)

      Example: Dynamic counters

      The following example contains 6 different dynamic values: a sender, a host, and four different programs.


      To avoid performance issues or even overloading syslog-ng OSE, you might want to limit the number of registered dynamic counters in the message statistics. To do this, configure the stats-max-dynamics() global option.

    • o - This object was once active, but stopped receiving messages. (For example, a dynamic object may disappear and become orphan.)

      NOTE: The syslog-ng OSE application stores the statistics of the objects when syslog-ng OSE is reloaded. However, if the configuration of syslog-ng OSE was changed since the last reload, the statistics of orphaned objects are deleted.

  5. The connections statistics counter displays the number of connections tracked by syslog-ng OSE for the selected source driver.

    Example: sample configuration and statistics output

    The following configuration will display the following syslog-ng-ctl statistics output:


    source s_network { 

    Statistics output:

  6. The type of the statistics:

    • batch_size_avg: When batching is enabled, then this shows the current average batch size of the given source or destination.

      NOTE: In version 7.0.27, syslog-ng OSE only supports the batch_size_avg for the http() destination.

    • batch_size_max: When batching is enabled, the value of batch_size_max shows the current largest batch size of the given source or destination.

      NOTE: In version 7.0.27, syslog-ng OSE only supports the batch_size_max for the http() destination.

    • discarded: The number of messages discarded by the given parser. These are messages that the parser could not parsed, and are therefore not processed. For example:

    • dropped: The number of dropped messages — syslog-ng OSE could not send the messages to the destination and the output buffer got full, so messages were dropped by the destination driver, or syslog-ng OSE dropped the message for some other reason (for example, a parsing error).

    • eps_last_1h: The EPS value of the past 1 hour.

    • eps_last_24h: The EPS value of the past 24 hours.

    • eps_since_start: The EPS value since the current syslog-ng OSE start.

      NOTE: When using the eps_last_1h, the eps_last_24h, and the eps_since_start statistics, consider the following:

      • EPS stands for "event per second", and in our case, a message received or sent counts as a single event.

      • The eps_last_1h, the eps_last_24h, and the eps_since_start values are only approximate values.

      • The eps_last_1h, the eps_last_24h, and the eps_since_start values are automatically updated every 60 seconds.

    • matched: The number of messages that are accepted by a given filter. Available for filters and similar objects (for example, a conditional rewrite rule). For example, if a filter matches a specific hostname, then the matched counter contains the number of messages that reached the filter from this hosts.

    • memory_usage: The memory used by the messages in the different queue types (in bytes). This includes every queue used by the object, including memory buffers (log-fifo) and disk-based buffers (both reliable and non-reliable). For example:;d_net#0;tcp,;a;memory_usage;0

      NOTE: The memory usage (size) of queues is not equal to the memory usage (size) of the log messages in syslog-ng OSE. A log message can be in multiple queues, thus its size is added to multiple queue sizes. To check the size of all log messages, use global.msg_allocated_bytes.value metric.

    • msg_size_max: The current largest message size of the given source or destination.

    • msg_size_avg: The current average message size of the given source or destination.

      NOTE: When using the msg_size_avg and msg_size_max statistics, consider that message sizes are calculated as follows:

      • on the source side: the length of the incoming raw message

      • on the destination side: the length of the outgoing formatted message

    • not_matched: The number of messages that are filtered out by a given filter. Available for filters and similar objects (for example, a conditional rewrite rule). For example, if a filter matches a specific hostname, then the not_matched counter contains the number of messages that reached the filter from other hosts, and so the filter discarded them.

      NOTE: Since the not_matched metric applies to filters, and filters are expected to discard messages that do not match the filter condition, not_matched messages are not included in the dropped metric of other objects.

    • processed: The number of messages that successfully reached their destination driver.

      NOTE: Consider that a message that has successfully reached its destination driver does not necessarily mean that the destination driver successfully delivered the messages as well. For example, a message can be written to disk or sent to a remote server after reaching the destination driver.

    • queued: The number of messages passed to the message queue of the destination driver, waiting to be sent to the destination.

    • stamp: The UNIX timestamp of the last message sent to the destination.

    • suppressed: The number of suppressed messages (if the suppress() feature is enabled).

    • written: The number of messages successfully delivered to the destination. This value is calculated from other counters: written = processed - queued - dropped. That is, the number of messages syslog-ng OSE passed to the destination driver (processed) minus the number of messages that are still in the output queue of the destination driver (queued) and the number of messages dropped because of an error (dropped, for example, because syslog-ng OSE could not deliver the message to the destination and exceeded the number of retries).

      This metric is calculated from other metrics. You cannot reset this metric directly: to reset it, you have to reset the metrics it is calculated from.

    NOTE: Consider that for syslog-ng OSE version 3.36, the following statistics counters are only supported for the http() destination, or the http() destination and all network() sources and destinations, and all file() sources and destinations, respectively:

    • msg_size_max

    • msg_size_avg

    • batch_size_max

    • batch_size_avg

    • eps_last_1h

    • eps_last_24h

    • eps_since_start

  7. The number of such messages.

Availability of statistics

Certain statistics are available only if the stats-level() global option is set to a higher value.

  • Level 0 collects only statistics about the sources and destinations.

  • Level 1 contains details about the different connections and log files, but has a slight memory overhead.

  • Level 2 contains detailed statistics based on the hostname.

  • Level 3 contains detailed statistics based on various message parameters like facility, severity, or tags.

When receiving messages with non-standard facility values (that is, higher than 23), these messages will be listed as other facility instead of their facility number.

Aggregated statistics

Aggregated statistics are available for different sources and destinations from different levels and upwards:









network() source and destination

from level 1

from level 1

counter N/A

counter N/A

from level 1

from level 1

from level 1

file() source and destination

from level 1

from level 1

counter N/A

counter N/A

from level 1

from level 1

from level 1

http() destination

from level 0


from level 0

from level 0

from level 0

from level 0

from level 0

from level 0

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Log statistics from the internal() source

If the stats-freq() global option is higher than 0, syslog-ng OSE periodically sends a log statistics message. This message contains statistics about the received messages, and about any lost messages since the last such message. It includes a processed entry for every source and destination, listing the number of messages received or sent, and a dropped entry including the IP address of the server for every destination where syslog-ng has lost messages. The center(received) entry shows the total number of messages received from every configured sources.

The following is a sample log statistics message for a configuration that has a single source (s_local) and a network and a local file destination (d_network and d_local, respectively). All incoming messages are sent to both destinations.

Log statistics;

The statistics include a list of source groups and destinations, as well as the number of processed messages for each. You can control the verbosity of the statistics using the stats-level() global option. The following is an example output.


The statistics are semicolon separated: every line contains statistics for a particular object (for example, source, destination, tag, and so on). The statistics have the following fields:

To reset the statistics to zero, use the following command: syslog-ng-ctl stats --reset

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Multithreading and scaling in syslog-ng OSE

Starting with version 3.3, syslog-ng OSE can process sources and destinations in multithreaded mode to scale to multiple CPUs or cores for increased performance. Starting with version 3.6, this multithreaded mode is the default.

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Multithreading concepts of syslog-ng OSE

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

NOTE: The way syslog-ng OSE uses multithreading may change in future releases. The current documentation applies to version 3.38.

syslog-ng OSE 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 OSE.

The maximum number of worker threads syslog-ng OSE uses is the number of CPUs or cores in the host running syslog-ng OSE (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 OSE can use, including the main syslog-ng OSE thread. However, the --worker-threads option does not affect the supervisor of syslog-ng OSE. 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 OSE.

When an event requiring a new thread occurs (for example, syslog-ng OSE receives new messages, or a destination becomes available), syslog-ng OSE 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() option. 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 OSE 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 OSE, in addition to the limit set in 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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