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read_syslog

Parses an incoming Syslog stream into events.

read_syslog [merge=bool, raw=bool, schema=string, selector=string, schema_only=bool, unflatten=string]

Description​

Syslog is a standard format for message logging.

Tenzir supports reading syslog messages in both the standardized "Syslog Protocol" format (RFC 5424), and the older "BSD syslog Protocol" format (RFC 3164).

Depending on the syslog format, the result can be different. Here's an example of a syslog message in RFC 5424 format:

<165>8 2023-10-11T22:14:15.003Z mymachineexamplecom evntslog 1370 ID47 [exampleSDID@32473 eventSource="Application" eventID="1011"] Event log entry

With this input, the parser will produce the following output, with the schema name syslog.rfc5424:

{
  "facility": 20,
  "severity": 5,
  "version": 8,
  "timestamp": "2023-10-11T22:14:15.003000",
  "hostname": "mymachineexamplecom",
  "app_name": "evntslog",
  "process_id": "1370",
  "message_id": "ID47",
  "structured_data": {
    "exampleSDID@32473": {
      "eventSource": "Application",
      "eventID": 1011
    }
  },
  "message": "Event log entry"
}

Here's an example of a syslog message in RFC 3164 format:

<34>Nov 16 14:55:56 mymachine PROGRAM: Freeform message

With this input, the parser will produce the following output, with the schema name syslog.rfc3164:

{
  "facility": 4,
  "severity": 2,
  "timestamp": "Nov 16 14:55:56",
  "hostname": "mymachine",
  "app_name": "PROGRAM",
  "process_id": null,
  "content": "Freeform message"
}

merge = bool (optional)​

Merges all incoming events into a single schema* that converges over time. This option is usually the fastest for reading highly heterogeneous data, but can lead to huge schemas filled with nulls and imprecise results. Use with caution.

*: In selector mode, only events with the same selector are merged.

raw = bool (optional)​

Use only the raw types that are native to the parsed format. Fields that have a type specified in the chosen schema will still be parsed according to the schema.

In the case of CEF, this means that no parsing of data takes place at all and every value remains a string, unless the field is in the schema.

schema = string (optional)​

Provide the name of a schema to be used by the parser.

If a schema with a matching name is installed, the result will always have all fields from that schema.

  • Fields that are specified in the schema, but did not appear in the input will be null.
  • Fields that appear in the input, but not in the schema will also be kept. schema_only=true can be used to reject fields that are not in the schema.

If the given schema does not exist, this option instead assigns the output schema name only.

The schema option is incompatible with the selector option.

selector = string (optional)​

Designates a field value as schema name with an optional dot-separated prefix.

The string is parsed as <fieldname>[:<prefix>]. The prefix is optional and will be prepended to the field value to generate the schema name.

For example, the Suricata EVE JSON format includes a field event_type that contains the event type. Setting the selector to event_type:suricata causes an event with the value flow for the field event_type to map onto the schema suricata.flow.

The selector option is incompatible with the schema option.

schema_only = bool (optional)​

When working with an existing schema, this option will ensure that the output schema has only the fields from that schema. If the schema name is obtained via a selector and it does not exist, this has no effect.

This option requires either schema or selector to be set.

unflatten = string (optional)​

A delimiter that, if present in keys, causes values to be treated as values of nested records.

A popular example of this is the Zeek JSON format. It includes the fields id.orig_h, id.orig_p, id.resp_h, and id.resp_p at the top-level. The data is best modeled as an id record with four nested fields orig_h, orig_p, resp_h, and resp_p.

Without an unflatten separator, the data looks like this:

Without unflattening
{
  id.orig_h: 1.1.1.1,
  id.orig_p: 10,
  id.resp_h: 1.1.1.2,
  id.resp_p: 5,
}

With the unflatten separator set to ., Tenzir reads the events like this:

With 'unflatten'
{
  id: {
    orig_h: 1.1.1.1,
    orig_p: 10,
    resp_h: 1.1.1.2,
    resp_p: 5,
  }
}

Examples​

Read in the auth.log​

Pipeline
load_file "/var/log/auth.log"
read_syslog
{
  facility: null,
  severity: null,
  timestamp: 2024-10-14T07:15:01.348027,
  hostname: "tenzirs-magic-machine",
  app_name: "CRON",
  process_id: "895756",
  content: "pam_unix(cron:session): session opened for user root(uid=0) by root(uid=0)",
}
{
  facility: null,
  severity: null,
  timestamp: 2024-10-14T07:15:01.349838,
  hostname: "tenzirs-magic-machine",
  app_name: "CRON",
  process_id: "895756",
  content: "pam_unix(cron:session): session closed for user root"
}