The syslog-ng application uses the following objects:
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Source driver: A communication method used to receive log messages. For example, syslog-ng can receive messages from a remote host via TCP/IP, or read the messages of a local application from a file. For details on source drivers, see Collecting log messages — sources and source drivers.
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Source: A named collection of configured source drivers.
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Destination driver: A communication method used to send log messages. For example, syslog-ng can send messages to a remote host via TCP/IP, or write the messages into a file or database. For details on destination drivers, see Sending and storing log messages — destinations and destination drivers.
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Destination: A named collection of configured destination drivers.
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Filter: An expression to select messages. For example, a simple filter can select the messages received from a specific host. For details, see Customizing message format using macros and templates.
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Macro: An identifier that refers to a part of the log message. For example, the ${HOST} macro returns the name of the host that sent the message. Macros are often used in templates and filenames. For details, see Customizing message format using macros and templates.
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Parser: Parsers are objects that parse the incoming messages, or parts of a message. For example, the csv-parser() can segment messages into separate columns at a predefined separator character (for example, a comma). Every column has a unique name that can be used as a macro. For details, see parser: Parse and segment structured messages and Processing message content with a pattern database.
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Rewrite rule: A rule modifies a part of the message, for example, replaces a string, or sets a field to a specified value. For details, see Modifying messages using rewrite rules.
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Log paths: A combination of sources, destinations, and other objects like filters, parsers, and rewrite rules. The syslog-ng application sends messages arriving from the sources of the log paths to the defined destinations, and performs filtering, parsing, and rewriting of the messages. Log paths are also called log statements. Log statements can include other (embedded) log statements and junctions to create complex log paths. For details, see Routing messages: log paths, flags, and filters.
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Template: A template is a set of macros that can be used to restructure log messages or automatically generate file names. For example, a template can add the hostname and the date to the beginning of every log message. For details, see Customizing message format using macros and templates.
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Option: Options set global parameters of syslog-ng, like the parameters of name resolution and timezone handling. For details, see Global options of syslog-ng PE.
For details on the above objects, see Global objects.
The syslog-ng application receives the timezone and daylight saving information from the operating system it is installed on. If the operating system handles daylight saving correctly, so does syslog-ng.
The syslog-ng application supports messages originating from different timezones. The original syslog protocol (RFC3164) does not include timezone information, but syslog-ng provides a solution by extending the syslog protocol to include the timezone in the log messages. The syslog-ng application also enables administrators to supply timezone information for legacy devices which do not support the protocol extension.
When syslog-ng PE receives a message, it assigns timezone information to the message using the following algorithm.
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The sender application (for example, the syslog-ng client) or host specifies the timezone of the messages. If the incoming message includes a timezone it is associated with the message. Otherwise, the local timezone is assumed.
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Specify the time-zone() parameter for the source driver that reads the message. This timezone will be associated with the messages only if no timezone is specified within the message itself. Each source defaults to the value of the recv-time-zone() global option. It is not possible to override only the timezone information of the incoming message, but setting the keep-timestamp() option to no allows syslog-ng PE to replace the full timestamp (timezone included) with the time the message was received.
NOTE: When processing a message that does not contain timezone information, the syslog-ng PE application will use the timezone and daylight-saving that was effective when the timestamp was generated. For example, the current time is 2011-03-11 (March 11, 2011) in the EU/Budapest timezone. When daylight-saving is active (summertime), the offset is +02:00. When daylight-saving is inactive (wintertime) the timezone offset is +01:00. If the timestamp of an incoming message is 2011-01-01, the timezone associated with the message will be +01:00, but the timestamp will be converted, because 2011-01-01 meant winter time when daylight saving is not active but the current timezone is +02:00.
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Specify the timezone in the destination driver using the time-zone() parameter. Each destination driver might have an associated timezone value: syslog-ng converts message timestamps to this timezone before sending the message to its destination (file or network socket). Each destination defaults to the value of the send-time-zone() global option.
NOTE: A message can be sent to multiple destination zones. The syslog-ng application converts the timezone information properly for every individual destination zone.
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Caution:
If syslog-ng PE sends the message is to the destination using the legacy-syslog protocol (RFC3164) which does not support timezone information in its timestamps, the timezone information cannot be encapsulated into the sent timestamp, so syslog-ng PE will convert the hour:min values based on the explicitly specified timezone. |
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If the timezone is not specified, local timezone is used.
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When macro expansions are used in the destination filenames, the local timezone is used. (Also, if the timestamp of the received message does not contain the year of the message, syslog-ng PE uses the local year.)
If the clients run syslog-ng, then use the ISO timestamp, because it includes timezone information. That way you do not need to adjust the recv-time-zone() parameter of syslog-ng.
If you want syslog-ng to output timestamps in Unix (POSIX) time format, use the S_UNIXTIME and R_UNIXTIME macros. You do not need to change any of the timezone related parameters, because the timestamp information of incoming messages is converted to Unix time internally, and Unix time is a timezone-independent time representation. (Actually, Unix time measures the number of seconds elapsed since midnight of Coordinated Universal Time (UTC) January 1, 1970, but does not count leap seconds.)
