Module log | Tarantool

Module log

Tarantool provides a set of options used to configure logging in various ways: you can set a level of logging, specify where to send the log’s output, configure a log format, and so on. The log module allows you to configure logging in your application and provides additional capabilities, for example, logging custom messages and rotating log files.

Below is a list of all log functions.

Name Use
log.cfg({}) Configure a logger
Log a message with the specified level Get the PID of a logger
log.rotate() Rotate a log file Create a new logger with the specified name

Configure logging options. The following options are available:

  • level: Specifies the level of detail the log has.

    Learn more: log_level.

  • log: Specifies where to send the log’s output, for example, to a file, pipe, or system logger.

    Learn more: log.

  • nonblock: If true, Tarantool does not block during logging when the system is not ready for writing, and drops the message instead.

    Learn more: log_nonblock.

  • format: Specifies the log format: ‘plain’ or ‘json’.

    Learn more: log_format.

  • modules: Configures the specified log levels for different modules.

    Learn more: log_modules.

The example below shows how to set the log level to ‘debug’ and how to send the resulting log to the ‘tarantool.log’ file:

log = require('log')
log.cfg{ level='debug', log='tarantool.log'}


Note that calling log.cfg() before box.cfg() takes into account logging options specified using environment variables, such as TT_LOG and TT_LOG_LEVEL.


Log a message with the specified logging level. You can learn more about the available levels from the log_level property description.

The example below shows how to log a message with the info level:

log = require('log')

-- Prints 'warn' messages --
log.warn('Warning message')
2023-07-20 11:03:57.029 [16300] main/103/interactive/tarantool [C]:-1 W> Warning message
  • message (any) –

    A log message.

    • A message can be a string.
    • A message may contain C-style format specifiers %d or %s. Example:
      log = require('log')'Info %s',
    • A message may be a scalar data type or a table. Example:
      log = require('log')
      log.error({500,'Internal error'})


The actual output will be a line in the log, containing:

  • the current timestamp
  • a module name
  • ‘E’, ‘W’, ‘I’, ‘V’ or ‘D’ depending on the called function
  • message

Note that the message will not be logged if the severity level corresponding to the called function is less than log_level.
Return:A PID of a logger. You can use this PID to send a signal to a log rotation program, so it can rotate logs.

Rotate the log. For example, you need to call this function to continue logging after a log rotation program renames or moves a file with the latest logs.


Since: 2.11.0

Create a new logger with the specified name. You can configure a specific log level for a new logger using the log_modules configuration property.

  • name (string) – a logger name

a logger instance


The code snippet below shows how to set the verbose level for module1 and the error level for module2:

box_cfg = { log_level = 'warn',
            log_modules = {
                module1 = 'verbose',
                module2 = 'error' }

To create the module1 and module2 loggers, call the new() function:

-- Creates new loggers --
module1_log = require('log').new('module1')
module2_log = require('log').new('module2')

Then, you can call functions corresponding to different logging levels to make sure that events with severities above or equal to the given levels are shown:

-- Prints 'info' messages --'Info message from module1')
[16300] main/103/interactive/module1 I> Info message from module1

-- Swallows 'debug' messages --
module1_log.debug('Debug message from module1')

-- Swallows 'info' messages --'Info message from module2')

At the same time, the events with severities below the specified levels are swallowed.

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