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syslog-ng Premium Edition 7.0.20 - 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 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 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 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 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 Glossary

How to empty disk-buffer files

This section describes how to empty disk-buffer files used in syslog-ng Premium Edition (syslog-ng PE).


Hazard of data loss!

You must stop log reception to be able to empty a disk-buffer. If you fail to stop log reception before emptying a disk-buffer, your newly received log messages may get stored in the disk-buffer, overwriting your previous log messages. To avoid log loss, One Identity recommends that you redirect your logs to a different syslog server when emptying your disk-buffer files.

NOTE: Consider the following while reading this section:

This section uses a simple example configuration with one source and one destination with disk-buffer.

If you are not aware of disk-buffers or you're not sure which of your destinations use disk-buffer, One Identity recommends that you do not proceed with the procedure of emptying your disk-buffer files. Instead, One Identity recommends that you contact our Support Team and open a service request. When opening the service request, describe your issue and attach a collected debug bundle from your system.

For more information about collecting a debug bundle for Microsoft Windows, see How to create a syslog-ng debug bundle archive on Windows operating system.

For more information about collecting a debug bundle for Linux or Unix OS, see How to create a syslog-ng debug bundle on Linux Or Unix operating system.


One Identity recommends that you empty your disk-buffer files before you begin the following:

  • Upgrading syslog-ng Premium Edition (syslog-ng PE) from version 6 to 7.

  • Changing the configuration of a remote destination with disk-buffer.

  • Applying a solution that includes the removal of the syslog-ng PE persistent file.

Example configuration for emptying disk-buffer files

The syslog-ng PE application uses the following example configuration to describe how to empty disk-buffer files:

source s_net { 
destination d_logserver { 
    network("" port(514) disk-buffer( disk-buf-size(2000000) ) );
log { 

To empty disk-buffer files,

  1. Name the disk-buffer file to empty and the destination statement using it.

    If you are not sure about which disk-buffer file to empty, or the destination statement using the disk-buffer file in question, you can use one of the following methods:

    • Check the list and the status of the disk-buffer files.

      • Non-empty disk-buffer file

        Disk-buffer state loaded; filename='/opt/syslog-ng/var/syslog-ng-00000.qf', qout_length='0', qbacklog_length='0', qoverflow_length='0', qdisk_length='3006'
      • IP:PORT information of the destination with the disk-buffer in use

        afsocket_dd_qfile(stream, = { "queue_file": "/opt/syslog-ng/var/syslog-ng-00000.qf" }

      For more information about getting information about disk-buffer files, see Useful information about disk-buffers.

    • Find the destination statement in the syslog-ng PE configuration using the IP:PORT information.

      destination d_logserver { network("" port(514) disk-buffer( disk-buf-size(2000000) ) ); };
  2. Locate the log statements that use the destination statement you named previously.

  3. Disable the sources in the log statements.

    Add '#' at the beginning of all source() entries in the log paths.

    log { 
  4. Reload syslog-ng PE by entering the /opt/syslog-ng/sbin/syslog-ng-ctl reload command.

  5. Check the disk-buffer file status.

    For more information, see Getting status information of disk-buffer files.

  6. To enable the sources again, remove '#' from the log paths and reload syslog-ng PE.

Enabling memory buffering

To enable memory buffering, use the log-fifo-size() parameter in the destination. All destination drivers can use memory buffering. Use memory buffering if you want to send logs to destinations where the disk-buffer option is not available, if you want the fastest solution, and if syslog-ng PE crash or network downtime is never expected. In these cases, losing logs is possible. This solution does not use the disk-buffer option. Instead, logs are stored only in the memory.

Example: Example for using memory buffering
destination d_BSD {

About disk queue files

Normal and reliable queue files

The key difference between disk queue files that employ the reliable(yes) option and not is the strategy they employ. Reliable disk queues guarantee that all the messages passing through them are written to disk first, and removed from the queue only after the destination has confirmed that the message has been successfully received. This prevents message loss, for example, due to syslog-ng PE crashes if the client and the destination server communicate using the Advanced Log Transfer Protocol (ALTP). Note that the Reliable Log Transfer Protocol is available only in syslog-ng Premium Edition version 6 LTS. Of course, using the reliable(yes) option introduces a significant performance penalty as well. Reliable disk queues employ an in-memory cache buffer, the content of which is also written to the disk, and which is intended to speed up the process of reading back data from the queue.

Normal disk queues work in a different way: they employ an in-memory output buffer (set in qout-size()) and an in-memory overflow queue (set in mem-buf-length()). The disk-buffer file itself is only used if the in-memory output buffer (set in qout-size()) is filled up completely. This approach has better performance (because of less disk IO operations), but also carries the risk of losing a maximum of qout-size() plus mem-buf-length() number of messages in case of an unexpected power failure or application crash.

Size and truncation of queue files

Disk queue files tend to grow. Each may take up to disk-buf-size() bytes on the disk. Due to the nature of reliable queue files, all the messages traversing the queue are written to disk, constantly increasing the size of the queue file. Truncation only occurs if the read and write heads of the queue reach the same position. Given that new messages arrive all the time, at least a small number of messages will almost always be stored in the queue file at all times. As a result, the queue file is not truncated automatically, but grows until it reaches the maximal configured size, after which the write head will wrap around, later followed by the read head.

In case of normal disk queue files, growth in size is not so apparent, as the disk-based queue file is only used if the in-memory overflow buffer fills up. Once the destination sends messages faster than the incoming message rate, the queue will start to empty, and when the read and write heads of the queue reach the same position, the queue files are finally truncated.

Note that if a queue file becomes corrupt, syslog-ng PE starts a new one. This might lead to the queue files consuming more space in total than their maximal configured size and the number of configured queue files multiplied together.


The following sections describe how to select and filter log messages.

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