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syslog-ng Open Source Edition 3.23 - 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 Logmatic.io 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

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 disk-based buffering is not available. Or if you want the fastest solution, and if syslog-ng OSE crash or network downtime is never expected. In these cases, losing logs is possible. This solution does not use disk-based buffering, logs are stored only in the memory.

Example: Example for using memory buffering
destination d_BSD {
    network("127.0.0.1"
        port(3333)
        log-fifo-size(10000)
    );
};

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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 OSE crashes if the client and the destination server communicate using the Reliable Log Transfer Protocol (RLTP). Note that the Reliable Log Transfer Protocol is available only in syslog-ng Premium Edition. 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 OSE 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.


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Filters

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


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Using filters

Filters perform log routing within syslog-ng: a message passes the filter if the filter expression is true for the particular message. If a log statement includes filters, the messages are sent to the destinations only if they pass all filters of the log path. For example, a filter can select only the messages originating from a particular host. Complex filters can be created using filter functions and logical boolean expressions.

To define a filter, add a filter statement to the syslog-ng configuration file using the following syntax:

filter <identifier> { <filter_type>("<filter_expression>"); };

Then use the filter in a log path, for example:

log {
    source(s1);
    filter(<identifier>);
    destination(d1); };

You can also define the filter inline. For details, see Defining configuration objects inline.

Example: A simple filter statement

The following filter statement selects the messages that contain the word deny and come from the host example.

filter demo_filter { host("example") and match("deny" value("MESSAGE"))
};
log {
    source(s1);
    filter(demo_filter);
    destination(d1);
};

The following example does the same, but defines the filter inline.

log {
    source(s1);
    filter { host("example") and match("deny" value("MESSAGE")) };
    destination(d1);
};

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