syslog-ng Open Source Edition 3.25 - 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 linux-audit: Collecting messages from Linux audit logs 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 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: Publishing messages to Apache Kafka (C implementation, using the librdkafka client) loggly: Using Loggly logmatic: Using mongodb: Storing messages in a MongoDB database 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 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 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 Glossary

TLS-encrypted message transfer

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Secure logging using TLS

The syslog-ng application can send and receive log messages securely over the network using the Transport Layer Security (TLS) protocol using the network() and syslog() drivers.


This chapter describes how to use TLS encryption when using the standard syslog protocols, that is, the network() and syslog() drivers, for example, to forward log messages between two syslog-ng nodes, or to send log data to syslog-ng Store Box or another log server. Other destinations that support TLS-encryption are not discussed in this chapter (for example, http()).

TLS uses certificates to authenticate and encrypt the communication, as illustrated on the following figure:

Figure 18: Certificate-based authentication

The client authenticates the server by requesting its certificate and public key. Optionally, the server can also request a certificate from the client, thus mutual authentication is also possible.

In order to use TLS encryption in syslog-ng, the following elements are required:

  • A certificate on the syslog-ng server that identifies the syslog-ng server.

  • The certificate of the Certificate Authority that issued the certificate of the syslog-ng server (or the self-signed certificate of the syslog-ng server) must be available on the syslog-ng client.

When using mutual authentication to verify the identity of the clients, the following elements are required:

  • A certificate must be available on the syslog-ng client. This certificate identifies the syslog-ng client.

  • The certificate of the Certificate Authority that issued the certificate of the syslog-ng client must be available on the syslog-ng server.

Mutual authentication ensures that the syslog-ng server accepts log messages only from authorized clients.

For more information about configuring TLS communication in syslog-ng, see Encrypting log messages with TLS.

For more information about TLS-related error messages, see Error messages.

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Encrypting log messages with TLS

This section describes how to configure TLS encryption in syslog-ng. For the concepts of using TLS in syslog-ng, see Secure logging using TLS.

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Configuring TLS on the syslog-ng clients


Complete the following steps on every syslog-ng client host. Examples are provided using both the legacy BSD-syslog protocol (using the network() driver) and the new IETF-syslog protocol standard (using the syslog() driver):

  1. Copy the CA certificate (for example, cacert.pem) of the Certificate Authority that issued the certificate of the syslog-ng server (or the self-signed certificate of the syslog-ng server) to the syslog-ng client hosts, for example, into the /opt/syslog-ng/etc/syslog-ng/ca.d directory.

    Issue the following command on the certificate: openssl x509 -noout -hash -in cacert.pem The result is a hash (for example, 6d2962a8), a series of alphanumeric characters based on the Distinguished Name of the certificate.

    Issue the following command to create a symbolic link to the certificate that uses the hash returned by the previous command and the .0 suffix.

    ln -s cacert.pem 6d2962a8.0

  2. Add a destination statement to the syslog-ng configuration file that uses the tls( ca-dir(path_to_ca_directory) ) option and specify the directory using the CA certificate. The destination must use the network() or the syslog() destination driver, and the IP address and port parameters of the driver must point to the syslog-ng server.

    Example: A destination statement using TLS

    The following destination encrypts the log messages using TLS and sends them to the 6514/TCP port of the syslog-ng server having the IP address.

    destination demo_tls_destination {
        network("" port(6514)
            tls( ca_dir("/opt/syslog-ng/etc/syslog-ng/ca.d"))

    A similar statement using the IETF-syslog protocol and thus the syslog() driver:

    destination demo_tls_syslog_destination {
        syslog("" port(6514)
  3. Include the destination created in Step 2 in a log statement.


    The encrypted connection between the server and the client fails if the Common Name or the subject_alt_name parameter of the server certificate does not contain the hostname or the IP address (as resolved from the syslog-ng clients and relays) of the server.

    Do not forget to update the certificate files when they expire.

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