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syslog-ng Premium Edition 7.0.32 - Administration Guide

Preface Introduction to syslog-ng The concepts of syslog-ng Installing syslog-ng PE 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 google-pubsub: collecting messages from the Google Pub/Sub messaging service wildcard-file: Collecting messages from multiple text files linux-audit: Collecting messages from Linux audit logs mssql, oracle, sql: collecting messages from an SQL database 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 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 udp-balancer: Receiving UDP messages at very high rate 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 google_pubsub(): Sending logs to the Google Cloud Pub/Sub messaging service google_pubsub-managedaccount(): Sending logs to the Google Cloud Pub/Sub messaging service authenticated by Google Cloud managed service account hdfs: Storing messages on the Hadoop Distributed File System (HDFS) http: Posting messages over HTTP kafka(): Publishing messages to Apache Kafka (Java implementation) (DEPRECATED) kafka-c(): Publishing messages to Apache Kafka using the librdkafka client (C implementation) 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 sentinel(): Sending logs to the Microsoft Azure Sentinel cloud snmp: Sending SNMP traps 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 Transport 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 Glossary

Monitoring statistics and metrics of syslog-ng

The syslog-ng PE application collects various statistics and measures different metrics about the messages it receives and delivers. These metrics are collected into different counters, depending on the configuration of syslog-ng PE. The stats-level() global option determines exactly which statistics syslog-ng PE collects. You can access these statistics and metrics using the following methods.

Recommended: Structured, selective methods:
Legacy: Unstructured, bulk methods:
  • Using the internal() source.

  • Using the syslog-ng-ctl stats command.

    For further information about using syslog-ng-ctl commands, see The syslog-ng control tool manual page.

  • Use the socat application: echo STATS | socat -vv UNIX-CONNECT:/opt/syslog-ng/var/run/syslog-ng.ctl -

  • If you have an OpenBSD-style netcat application installed, use the echo STATS | nc -U /opt/syslog-ng/var/run/syslog-ng.ctl command. Note that the netcat included in most Linux distributions is a GNU-style version that is not suitable to query the statistics of syslog-ng.

Metrics and counters of syslog-ng PE

You can list all active metrics on your syslog-ng PE 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 PE, 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 PE application stores the statistics of the objects when syslog-ng PE is reloaded. However, if the configuration of syslog-ng PE 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 PE 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 PE 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 PE 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 PE 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 PE 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 PE 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.

    • license_host_usage: The number of consumed licensed hosts since the latest syslog-ng startup or the latest periodic license reset (provided that reset-license-counter() option is turned on). This statistics counter is only registered if we have a valid limited license. For example:

    • license_monthly_consumed_hosts: The number of consumed licensed hosts since the latest monthly license report. This statistics counter is only registered if we have a valid and limited license, moreover the option report-host-usage() is turned on. For example:

    • 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 PE. 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 PE 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 PE 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 PE version 7.0.27, 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

Log statistics from the internal() source

If the stats-freq() global option is higher than 0, syslog-ng PE 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

The monitoring() source

The monitoring() source allows you to select which statistics of syslog-ng PE you want to monitor. In addition, the statistics are available as structured name-value pairs, so you can format the output similarly to other log messages. That way, you can easily convert the statistics and metrics, for example, into JSON or WELF format. That way, you can send the statistics of your log messages into a monitoring solution.

The monitoring() source queries the statistics (counters) that syslog-ng PE collects, formats them, and optionally resets the counters. The monitoring() source emits only these messages, making it easy to route them to their appropriate destination. The stats-level() global option determines exactly which statistics syslog-ng PE collects.

source s_monitor{
Example: Save all statistics into a file in JSON format

The following configuration increases the stats-level() option to 3, and generates a JSON-formatted message every 10 seconds. The generated message contains every available statistics, and is saved into the /var/log/syslog-ng-statistics.log file.

@version: 7.0 
options { 

source s_monitor { monitoring( 
    message-template("$(format-flat-json --scope nv_pairs)") 
destination d_file { 
log { 

The generated message is similar to this one:

[2021-09-02T13:30:18.003557] Outgoing message; message='Sep 2 13:30:18 test-host syslog-ng[71345]: {"tag..source.s_monitor.processed":"111","src.severity.7.processed":"0","src.severity.6.processed":"111","src.severity.5.processed":"0","src.severity.4.processed":"0","src.severity.3.processed":"0","src.severity.2.processed":"0","src.severity.1.processed":"0","src.severity.0.processed":"0","src.sender.s_monitor#0.test-host.stamp":"1630582216","src.sender.s_monitor#0.test-host.processed":"111","src.sender.test-host.stamp":"1630582216","src.sender.test-host.processed":"111","src.program.syslog-ng.stamp":"1630582216","src.program.syslog-ng.processed":"111","src.monitoring.s_monitor#0.stamp":"1630582216","src.monitoring.s_monitor#0.processed":"111","":"1630582216","":"111","":"1630582216","":"111","' 

For reference, the JSON part in a readable format is:

{ "tag..source.s_monitor.processed": "111", "src.severity.7.processed": "0", "src.severity.6.processed": "111", "src.severity.5.processed": "0", "src.severity.4.processed": "0", "src.severity.3.processed": "0", "src.severity.2.processed": "0", "src.severity.1.processed": "0", "src.severity.0.processed": "0", "src.sender.s_monitor#0.test-host.stamp": "1630582216", "src.sender.s_monitor#0.test-host.processed": "111", "src.sender.test-host.stamp": "1630582216", "src.sender.test-host.processed": "111", "src.program.syslog-ng.stamp": "1630582216", "src.program.syslog-ng.processed": "111", "src.monitoring.s_monitor#0.stamp": "1630582216", "src.monitoring.s_monitor#0.processed": "111", "": "1630582216", "": "111", "": "1630582216", "": "111", "src.facility.other.processed": "0", "src.facility.9.processed": "0", "src.facility.8.processed": "0", "src.facility.7.processed": "0", "src.facility.6.processed": "0", "src.facility.5.processed": "111", "src.facility.4.processed": "0", "src.facility.3.processed": "0", "src.facility.23.processed": "0", "src.facility.22.processed": "0", "src.facility.21.processed": "0", "src.facility.20.processed": "0", "src.facility.2.processed": "0", "src.facility.19.processed": "0", "src.facility.18.processed": "0", "src.facility.17.processed": "0", "src.facility.16.processed": "0", "src.facility.15.processed": "0", "src.facility.14.processed": "0", "src.facility.13.processed": "0", "src.facility.12.processed": "0", "src.facility.11.processed": "0", "src.facility.10.processed": "0", "src.facility.1.processed": "0", "src.facility.0.processed": "0", "source.s_monitor.processed": "111", "global.sdata_updates.processed": "0", "global.scratch_buffers_count.queued": "280", "global.scratch_buffers_bytes.queued": "50944", "global.payload_reallocs.processed": "557", "global.msg_clones.processed": "0", "global.msg_allocated_bytes.value": "1056", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.written": "111", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.truncated_count": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.truncated_bytes": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.queued": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.processed": "111", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.msg_size_max": "3019", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.msg_size_avg": "2991", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.memory_usage": "0", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.eps_since_start": "1", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.eps_last_24h": "1", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.eps_last_1h": "1", "dst.file.d_file#0./var/log/syslog-ng-statistics.log.dropped": "0", "destination.d_file.processed": "111", "center.received.processed": "111", "center.queued.processed": "111", "PROGRAM": "syslog-ng", "PID": "71345" } 
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