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syslog-ng Open Source Edition 3.30 - 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 Sumo Logic destinations: sumologic-http() and sumologic-syslog() 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

Options of JSON parsers

The JSON parser has the following options.

extract-prefix()
Synopsis: extract-prefix()

Description: Extract only the specified subtree from the JSON message. Use the dot-notation to specify the subtree. The rest of the message will be ignored. For example, assuming that the incoming object is named msg, the json-parser(extract-prefix("foo.bar[5]")); parser is equivalent to the msg.foo.bar[5] javascript code. Note that the resulting expression must be a JSON object in order to extract its members into name-value pairs.

This feature also works when the top-level object is an array, because you can use an array index at the first indirection level, for example: json-parser(extract-prefix("[5]")), which is equivalent to msg[5].

In addition to alphanumeric characters, the key of the JSON object can contain the following characters: !"#$%&'()*+,-/:;<=>?@\^_`{|}~

It cannot contain the following characters: .[]

Example: Convert logstash eventlog format v0 to v1

The following parser converts messages in the logstash eventlog v0 format to the v1 format.

parser p_jsoneventv0 {
    channel {
        parser {
            json-parser(extract-prefix("@fields"));
        };
        parser {
            json-parser(prefix(".json."));
        };
        rewrite {
            set("1" value("@version"));
            set("${.json.@timestamp}" value("@timestamp"));
            set("${.json.@message}" value("message"));
        };
    };
};
marker
Synopsis: marker()

Description: Use a marker in case of mixed log messages, to identify JSON encoded messages for the parser.

Some logging implementations require a marker to be set before the JSON payload. The JSON parser is able to find these markers and parse the message only if it is present.

Example: Using the marker option in JSON parser

This json parser parses log messages which use the "@cee:" marker in front of the json payload. It inserts ".cee." in front of the name of name-value pairs, so later on it is easier to find name-value pairs that were parsed using this parser. (For details on selecting name-value pairs, see value-pairs().)

parser {
        json-parser(
            marker("@cee:")
            prefix(".cee.")
        );
    };
prefix()
Synopsis: prefix()

Description: Insert a prefix before the name part of the parsed name-value pairs to help further processing. For example:

  • To insert the my-parsed-data. prefix, use the prefix(my-parsed-data.) option.

  • To refer to a particular data that has a prefix, use the prefix in the name of the macro, for example, ${my-parsed-data.name}.

  • If you forward the parsed messages using the IETF-syslog protocol, you can insert all the parsed data into the SDATA part of the message using the prefix(.SDATA.my-parsed-data.) option.

Names starting with a dot (for example, .example) are reserved for use by syslog-ng OSE. If you use such a macro name as the name of a parsed value, it will attempt to replace the original value of the macro (note that only soft macros can be overwritten, see Hard versus soft macros for details). To avoid such problems, use a prefix when naming the parsed values, for example, prefix(my-parsed-data.)

template()
Synopsis: template("${<macroname>}")

Description: The macro that contains the part of the message that the parser will process. It can also be a macro created by a previous parser of the log path. By default, the parser processes the entire message (${MESSAGE}).

XML parser

Extensible Markup Language (XML) is a text-based open standard designed for both human-readable and machine-readable data interchange. Like JSON, it is used primarily to transmit data between a server and web application. It is described in W3C Recommendation: Extensible Markup Language (XML).

The XML parser processes input in XML format, and adds the parsed data to the message object.

To create an XML parser, define an xml_parser that has the xml() option. By default, the parser will process the ${MESSAGE} part of the log message. To process other parts of a log message using the XML parser, use the template() option. You can also define the parser inline in the log path.

Declaration:
parser xml_name {
    xml(
        template()
        prefix()
        drop-invalid()
        exclude-tags()
        strip-whitespaces()
    );
};
Example: Using an XML parser

In the following example, the source is an XML-encoded log message. The destination is a file that uses the format-json template. The log line connects the source, the destination and the parser.

source s_local {
    file("/tmp/aaa");
};

destination d_local {
    file(
        "/tmp/bbb"
        template("$(format-json .xml.*)\n")
    );
};

parser xml_parser {
    xml();
};

log {
    source(s_local);
    parser(xml_parser);
    destination(d_local);
};

You can also define the parser inline in the log path.

log {
    source(s_file);
    parser { xml(prefix(".SDATA")); };
    destination(d_file);
};

The XML parser inserts an ".xml" prefix by default before the extracted name-value pairs. Since format-json replaces a dot with an underscore at the beginning of keys, the ".xml" prefix becomes "_xml". Attributes get an _ prefix. For example, from the XML input:

<tags attr='attrval'>part1<tag1>Tag1 Leaf</tag1>part2<tag2>Tag2 Leaf</tag2>part3</tags>

The following output is generated:

{"_xml":{"tags":{"tag2":"Tag2 Leaf","tag1":"Tag1 Leaf","_attr":"attrval","tags":"part1part2part3"}}}

When the text is separated by tags on different levels or tags on the same level, the parser simply concatenates the different parts of text. For example, from this input XML:

<tag>
 <tag1>text1</tag1>
 <tag1>text2</tag1>
</tag>

The following output is generated:

.xml.tag.tag1 = text1text2

Whitespaces are kept as they are in the XML input. No collapsing happens on significant whitespaces. For example, from this input XML:

<133>Feb 25 14:09:07 webserver syslogd: <b>|Test\n\n   Test2|</b>\n

The following output is generated:

[2017-09-04T13:20:27.417266] Setting value; msg='0x7f2fd8002df0', name='.xml.b', value='|Test\x0a\x0a   Test2|'

However, note that users can choose to strip whitespaces using the strip-whitespaces() option.

Configuration hints

Define a source that correctly detects the end of the message, otherwise the XML parser will consider the input invalid, resulting in a parser error.

To ensure that the end of the XML document is accurately detected, use any of the following options:

  • Ensure that the XML is a single-line message.

  • In the case of multiline XML documents:

    • If the opening and closing tags are fixed and known, you can use multi-line-mode(prefix-suffix). Using regular expressions, specify a prefix and suffix matching the opening and closing tags. For details on using multi-line-mode(prefix-suffix), see the multi-line-prefix() and multi-line-suffix() options.

    • In the case of TCP, you can encapsulate and send the document in syslog-protocol format, and use a syslog() source. Make sure that the message conforms to the octet counting method described in RFC6587.

      For example:

      59 <133>Feb 25 14:09:07 webserver syslogd: <book>\nText\n</book>

      Considering the new lines as one character, 59 is appended to the original message.

    • You can use a datagram-based source. In the case of datagram-based sources, the protocol signals the end of the message automatically. Ensure that the complete XML document is written in one message.

    • Unless the opening and closing tags are fixed and known, stream-based sources are currently not supported.

In case you experience issues, start syslog-ng with debug logs enabled. There will be a debug log about the incoming log entry, which shows the complete message to be parsed. The entry should contain the entire XML document.

NOTE: If your log messages are entirely in .xml format, make sure to disable any message parsing on the source side by including the flags("no-parse") option in your source statement. This will put the entire log message in the $MESSAGE macro, which is the field that the XML parser parses by default.

Limitations of the XML parsers

The XML parser comes with certain limitations.

Vector-like structures:

It is not possible to address each element of a vector-like structure individually. For example, take this input:

<vector>
    <entry>value1</entry>
    <entry>value2</entry>
    ...
    <entry>valueN</entry>
</vector>

After parsing, the entries cannot be addressed individually. Instead, the text of the entries will be concatenated:

vector.entry = "value1value2...valueN"

Note that xmllint has the same behavior:

$ xmllint --xpath "/vector/entry/text()" test.xml
value1value2valueN%
CDATA:

The XML parser does not support CDATA. CDATA inside the XML input is ignored. This is true for the processing instructions as well.

Inherited limitations:

The XML parser is based on the glib XML subset parser, called "GMarkup" parser, which is not a full-scale XML parser. It is intended to parse a simple markup format that is a subset of XML. Some limitations are inherited:

  • Do not use the XML parser if you expect to interoperate with applications generating full-scale XML. Instead, use it for application data files, configuration files, log files, and so on, where you know your application will be the only one writing the file.

  • The XML parser is not guaranteed to display an error message in the case of invalid XML. It may accept invalid XML. However, it does not accept XML input that is not well-formed (a condition that is weaker than requiring XML to be valid).

No support for long keys:

If the key is longer than 255 characters, syslog-ng drops the entry and an error log is emitted. There is no chunking or any other way of recovering data, not even partial data. The entry will be replaced by an empty string.

Options of the XML parsers

The XML parser has the following options.

drop-invalid
Synopsis: drop-invalid()
Format: yes|no
Default: no
Mandatory: no

Description: If set, messages with an invalid XML will be dropped entirely.

exclude-tags
Synopsis: exclude-tags()
Format: list of globs
Default:

None

If not set, no filtering is done.

Mandatory: no

Description: The XML parser matches tags against the listed globs. If there is a match, the given subtree of the XML will be omitted.

Example: Using exclude_tags
parser xml_parser {
    xml(
        template("$MSG")
        exclude-tags("tag1", "tag2", "inner*")
    );
};

From this XML input:

<tag1>Text1</tag1><tag2>Text2</tag2><tag3>Text3<innertag>TextInner</innertag></tag3>

The following output is generated:

{"_xml":{"tag3":"Text3"}}
prefix()
Synopsis: prefix()

Description: Insert a prefix before the name part of the parsed name-value pairs to help further processing. For example:

  • To insert the my-parsed-data. prefix, use the prefix(my-parsed-data.) option.

  • To refer to a particular data that has a prefix, use the prefix in the name of the macro, for example, ${my-parsed-data.name}.

  • If you forward the parsed messages using the IETF-syslog protocol, you can insert all the parsed data into the SDATA part of the message using the prefix(.SDATA.my-parsed-data.) option.

Names starting with a dot (for example, .example) are reserved for use by syslog-ng OSE. If you use such a macro name as the name of a parsed value, it will attempt to replace the original value of the macro (note that only soft macros can be overwritten, see Hard versus soft macros for details). To avoid such problems, use a prefix when naming the parsed values, for example, prefix(my-parsed-data.)

The prefix() option is optional and its default value is ".xml".

strip-whitespaces
Synopsis: strip-whitespaces()
Format: yes|no
Default: no
Mandatory: no

Description: Strip the whitespaces from the XML text nodes before adding them to the message.

Example: Using strip-whitespaces
parser xml_parser {
    xml(
        template("$MSG")
        strip-whitespaces(yes)
    );
};

From this XML input:

<tag1> Tag </tag1>

The following output is generated:

{"_xml":{"tag1":"Tag"}}
template()
Synopsis: template("${<macroname>}")

Description: The macro that contains the part of the message that the parser will process. It can also be a macro created by a previous parser of the log path. By default, the parser processes the entire message (${MESSAGE}).

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