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syslog-ng Premium Edition 7.0.18 - 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 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 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 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

Enabling the normal disk-buffer option

The following destination drivers can use the disk-buffer option: elasticsearch2(), file(), hdfs(), kafka(), mongodb(), program(), riemann(), smtp(),sql(), unix-dgram(), and unix-stream(). The network(), syslog(), tcp(), and tcp6() destination drivers can also use the disk-buffer option, except when using the udp transport method. (The other destinations or protocols do not provide the necessary feedback mechanisms required for the disk-buffer option.)

To enable the normal disk-buffer option, use the disk-buffer(reliable(no)) parameter in the destination. Use the normal disk-buffer option if you want a solution that is faster than the reliable disk-buffer option. In this case, the process will be less reliable and it is possible to lose logs in case of syslog-ng PE crash. The filename of the normal disk-buffer file is the following: <syslog-ng path>/var/syslog-ng-00000.qf.

Example: Example for using the normal disk-buffer option

When using the plugin for the disk-buffer file

destination d_BSD {
    network(
            "127.0.0.1"
            port(3333)
            disk-buffer(
                mem-buf-length(10000)
                disk-buf-size(2000000)
                reliable(no)
            )
        );
        }; 

For more details on the differences between the normal and the reliable disk-buffer options, see About disk queue files.

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 {
    network(
            "127.0.0.1"
            port(3333)
            log-fifo-size(10000)
        );
};

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.

Filters

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

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