= Trac Logging
[[TracGuideToc]]

Trac supports logging of system messages using Python's [https://docs.python.org/2/library/logging.html logging module].

Logging is configured in the [TracIni#logging-section "[logging]"] section of TracIni.

== Supported Logging Methods

The log method is set using the [TracIni#logging-log_type-option "[logging] log_type"] option, which accepts the following values:

 '''none'':: Suppress all log messages.
 '''file''':: Log messages to a file, specified with the [TracIni#logging-log_file-option "[logging] log_file"] option. Relative paths for `log_file` are resolved relative to the environment `log` directory.
 '''stderr''':: Output log entries to console ([TracStandalone tracd] only).
 '''syslog''':: (UNIX) Send log messages to the local syslogd via named pipe `/dev/log`. By default, syslog will write them to the `/var/log/messages` file.
 '''eventlog''':: (Windows) Use the system's NT Event Log.

== Log Levels

The verbosity level of logged messages can be set using the [TracIni#logging-log_level-option "[logging] log_level"] option. The log level defines the minimum level of urgency required for a message to be logged, and those levels are:

 '''CRITICAL''':: Log only the most critical (typically fatal) errors.
 '''ERROR''':: Log failures, bugs and errors. 
 '''WARN''':: Log warnings, non-interrupting events.
 '''INFO''':: Diagnostic information, log information about all processing.
 '''DEBUG''':: Trace messages, profiling, etc.

Additionally, you can  enable logging of SQL statements at debug level. This is turned off by default, as it's very verbose. Set [TracIni#trac-debug_sql-option "[trac] debug_sql  = yes"] to activate.

== Log Format

The output format for log entries can be specified in the [TracIni#logging-log_format-option "[logging] log_format"] option. The format is a string which can contain any of the [https://docs.python.org/2/library/logging.html#logrecord-attributes Python logging Formatter variables]. Additionally, the following Trac-specific variables can be used:
 '''$(basename)s''':: The environment directory name.
 '''$(path)s''':: The absolute path of the environment directory.
 '''$(project)s''':: The originating project's name.

Note that variables are identified using a dollar sign (`$(...)s`) instead of percent sign (`%(...)s`).

The default format is:
{{{#!ini
log_format = Trac[$(module)s] $(levelname)s: $(message)s
}}}

In a multi-project environment where all logs are sent to the same place (e.g. `syslog`), it makes sense to add the project name. In this example we use `basename` since that can generally be used to identify a project:
{{{#!ini
log_format = Trac[$(basename)s:$(module)s] $(levelname)s: $(message)s
}}}

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See also: TracIni, TracEnvironment