Syslog Messages

Syslog messages sent over the network to Meridian can be transformed into events according to preconfigured rules.

Syslogd, which enables Meridian to receive syslog messages over the network, must be enabled for this functionality to work. This daemon is disabled by default.

Parsers

You can use parsers to convert syslog message fields into Meridian event fields.

Syslog message parsers
Parser	Description
org.opennms.netmgt.syslogd.CustomSyslogParser	Uses a regex statement to parse the syslog header.
org.opennms.netmgt.syslogd.RadixTreeSyslogParser	Uses an internal list of Grok-style statements to parse the syslog header.
org.opennms.netmgt.syslogd.SyslogNGParser	Strictly parses messages in the default pattern of syslog-ng.
org.opennms.netmgt.syslogd.Rfc5424SyslogParser	Strictly parses the RFC 5424 format for syslog messages.

RadixTreeSyslogParser

The RadixTreeSyslogParser normally uses a set of internally defined patterns to parse multiple syslog message formats. To customize the set of patterns, modify ${OPENNMS_HOME}/etc/syslogd-grok-patterns.txt.

The patterns are defined in Grok-style statements where each token is defined by a %{PATTERN:semantic} clause. Whitespace in the pattern will match 0…n whitespace characters, and character literals in the pattern will match the corresponding characters. The % character literal must be escaped by using a backslash (for example, \%).

The RadixTreeSyslogParser Grok implementation supports only a limited number of pattern types. However, these patterns should be sufficient to parse any syslog message format.

Arrange the patterns in the file from most specific to least specific, since the first pattern to successfully match the syslog message will be used to construct the Meridian event.

`RadixTreeSyslogParser` parameter patterns
Pattern	Description
HOSTNAME	String containing only valid hostname characters (alphanumeric plus '.', '-' and '_').
HOSTNAMEORIP	String containing only valid hostname characters or IP address characters (IPv4 or IPv6).
INT	Positive integer
IPADDRESS	String containing only valid IP address characters (IPv4 or IPv6).
MONTH	Three-character English abbreviation of the month.
NOSPACE	String that contains no whitespace.
STRING	String. Because this matches any character, it must be followed by a delimiter in the pattern string.
WHITESPACE	String that contains only whitespace (spaces and tabs).

`RadixTreeSyslogParser` semantic tokens
Semantic Token	Description
day	Two-digit day of month (01-31)
facilityPriority	Facility-priority integer
hostname	String hostname (unqualified or FQDN), IPv4 address, or IPv6 address.
hour	Two-digit hour of day (00-23)
message	Remaining string message.
messageId	String message ID
minute	Two-digit minute (0-59)
month	Two-digit month (01-12)
parm*	Generic string parameter where the parameter’s key is the identifier following "parm" in the semantic token (for example, `parmComponentId` maps to a string parameter with key "ComponentId").
processId	String process ID
processName	String process name
second	Two-digit second (00-59)
secondFraction	One- to six-digit fractional second value as a string.
timezone	String timezone value
version	Version
year	Four-digit year

Examples

There are some sample syslog event parsing definitions in ${OPENNMS_HOME}/etc/syslog you can use as a base for customizing your own event parsing.

Discard messages

If there are syslog messages you do not want to keep, you can set the UEI to DISCARD-MATCHING-MESSAGES. This will flag the message as donotpersist so it will be dropped and not written to the database.

<ueiMatch>
    <match type="regex" expression="^.*(\[api-status-warning\].*deprecated).*$" />
    <uei>DISCARD-MATCHING-MESSAGES</uei>
</ueiMatch>

Facility/Severity filtering

If you have similar messages coming in with different syslog facility or severity flags, but only want to capture events that match a specific value, you can specify a filter in the syslogd configuration.

<ueiMatch>
    <facility>local0</facility>
    <severity>Warning</severity>
    <match type="regex" expression="^.*Certificate (.*) expired on (.*)$" />
    <uei>uei.opennms.org/custom/syslog/certExpired</uei>
    <parameter-assignment matching-group="1" parameter-name="certName" />
    <parameter-assignment matching-group="2" parameter-name="expireDate" />
</ueiMatch>