Logging example
Logging example

Logging example


What level of detail the log will have. There are seven levels:

  • 1 – SYSERROR
  • 2 – ERROR
  • 3 – CRITICAL
  • 4 – WARNING
  • 5 – INFO
  • 6 – VERBOSE
  • 7 – DEBUG

By setting log_level, one can enable logging of all classes below or equal to the given level. Tarantool prints its logs to the standard error stream by default, but this can be changed with the log configuration parameter.

Type: integer
Default: 5
Dynamic: yes

Warning: prior to Tarantool 1.7.5 there were only six levels and DEBUG was level 6. Starting with Tarantool 1.7.5 VERBOSE is level 6 and DEBUG is level 7. VERBOSE is a new level for monitoring repetitive events which would cause too much log writing if INFO were used instead.


By default, Tarantool sends the log to the standard error stream (stderr). If log is specified, Tarantool sends the log to a file, or to a pipe, or to the system logger.

Example setting for sending the log to a file:

box.cfg{log = 'tarantool.log'}
-- or
box.cfg{log = 'file:tarantool.log'}

This will open the file tarantool.log for output on the server’s default directory. If the log string has no prefix or has the prefix “file:”, then the string is interpreted as a file path.

Example setting for sending the log to a pipe:

box.cfg{log = '| cronolog tarantool.log'}
-- or
box.cfg{log = 'pipe: cronolog tarantool.log'}'

This will start the program cronolog when the server starts, and will send all log messages to the standard input (stdin) of cronolog. If the log string begins with ‘|’ or has the prefix “pipe:”, then the string is interpreted as a Unix pipeline.

Example setting for sending the log to syslog:

box.cfg{log = 'syslog:identity=tarantool'}
-- or
box.cfg{log = 'syslog:facility=user'}
-- or
box.cfg{log = 'syslog:identity=tarantool,facility=user'}
-- or
box.cfg{log = 'syslog:server=unix:/dev/log'}

If the log string begins with “syslog:”, then it is interpreted as a message for the syslogd program which normally is running in the background of any Unix-like platform. The setting can be ‘syslog:’, ‘syslog:facility=…’, ‘syslog:identity=…’, ‘syslog:server=…’, or a combination.

The syslog:identity setting is an arbitrary string which will be placed at the beginning of all messages. The default value is: tarantool.

The syslog:facility setting is currently ignored but will be used in the future. The value must be one of the syslog keywords, which tell syslogd where the message should go. The possible values are: auth, authpriv, cron, daemon, ftp, kern, lpr, mail, news, security, syslog, user, uucp, local0, local1, local2, local3, local4, local5, local6, local7. The default value is: user.

The syslog:server setting is the locator for the syslog server. It can be a Unix socket path beginning with “unix:”, or an ipv4 port number. The default socket value is: dev/log (on Linux) or /var/run/syslog (on Mac OS). The default port value is: 514, the UDP port.

When logging to a file, Tarantool reopens the log on SIGHUP. When log is a program, its pid is saved in the log.logger_pid variable. You need to send it a signal to rotate logs.

Type: string
Default: null
Dynamic: no

If log_nonblock equals true, Tarantool does not block on the log file descriptor when it’s not ready for write, and drops the message instead. If log_level is high, and many messages go to the log file, setting log_nonblock to true may improve logging performance at the cost of some log messages getting lost.

This parameter has effect only if the output is going to syslog or to a pipe.

Type: boolean
Default: true
Dynamic: no

If processing a request takes longer than the given value (in seconds), warn about it in the log. Has effect only if log_level is more than or equal to 4 (WARNING).

Type: float
Default: 0.5
Dynamic: yes

Log entries have two possible formats:

  • ‘plain’ (the default), or
  • ‘json’ (with more detail and with JSON labels).

Here is what a log entry looks like after box.cfg{log_format='plain'}:

2017-10-16 11:36:01.508 [18081] main/101/interactive I> set 'log_format' configuration option to "plain"

Here is what a log entry looks like after box.cfg{log_format='json'}:

{"time": "2017-10-16T11:36:17.996-0600",
"level": "INFO",
"message": "set 'log_format' configuration option to \"json\"",
"pid": 18081,|
"cord_name": "main",
"fiber_id": 101,
"fiber_name": "interactive",
"file": "builtin\/box\/load_cfg.lua",
"line": 317}

The log_format='plain' entry has time, process id, cord name, fiber_id, fiber_name, log level, and message.

The log_format='json' entry has the same things along with their labels, and in addition has the file name and line number of the Tarantool source.

Type: string
Default: ‘plain’
Dynamic: yes

Logging example

This will illustrate how “rotation” works, that is, what happens when the server instance is writing to a log and signals are used when archiving it.

Start with two terminal shells, Terminal #1 and Terminal #2.

On Terminal #1: start an interactive Tarantool session, then say the logging will go to Log_file, then put a message “Log Line #1” in the log file:

log = require('log')'Log Line #1')

On Terminal #2: use mv so the log file is now named Log_file.bak. The result of this is: the next log message will go to Log_file.bak.

mv Log_file Log_file.bak

On Terminal #1: put a message “Log Line #2” in the log file.'Log Line #2')

On Terminal #2: use ps to find the process ID of the Tarantool instance.

ps -A | grep tarantool

On Terminal #2: use kill -HUP to send a SIGHUP signal to the Tarantool instance. The result of this is: Tarantool will open Log_file again, and the next log message will go to Log_file. (The same effect could be accomplished by executing log.rotate() on the instance.)

kill -HUP process_id

On Terminal #1: put a message “Log Line #3” in the log file.'Log Line #3')

On Terminal #2: use less to examine files. Log_file.bak will have these lines, except that the date and time will depend on when the example is done:

2015-11-30 15:13:06.373 [27469] main/101/interactive I> Log Line #1`
2015-11-30 15:14:25.973 [27469] main/101/interactive I> Log Line #2`

and Log_file will have

log file has been reopened
2015-11-30 15:15:32.629 [27469] main/101/interactive I> Log Line #3


By default a Tarantool daemon sends a small packet once per hour, to The packet contains three values from,, and By changing the feedback configuration parameters, users can adjust or turn off this feature.


Whether to send feedback.

If this is set to true, feedback will be sent as described above. If this is set to false, no feedback will be sent.

Type: boolean
Default: true
Dynamic: yes

The address to which the packet is sent. Usually the recipient is Tarantool, but it can be any URL.

Type: string
Dynamic: yes

The number of seconds between sendings, usually 3600 (1 hour).

Type: float
Default: 3600
Dynamic: yes