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Command-Line Options for Logging

Log levels and topics

ArangoDB’s log output is grouped into topics. --log.level can be specified multiple times at startup, for as many topics as needed. The log verbosity and output files can be adjusted per log topic. For example

--log.level startup=trace --log.level queries=trace --log.level info

will log messages concerning startup at trace level, AQL queries at trace level and everything else at info level.

In a configuration file, it is written like this:

level = startup=trace
level = queries=trace
level = info

Note that there must not be any whitespace around the second =.

The available log levels are:

  • fatal: only logs fatal errors
  • error: only logs errors
  • warning: only logs warnings and errors
  • info: logs information messages, warnings and errors
  • debug: logs debug and information messages, warnings and errors
  • trace: logs trace, debug and information messages, warnings and errors

Note that levels debug and trace will be very verbose.

Some relevant log topics available in ArangoDB 3 are:

  • agency: information about the agency
  • collector: information about the WAL collector’s state
  • compactor: information about the collection datafile compactor
  • datafiles: datafile-related operations
  • mmap: information about memory-mapping operations (including msync)
  • performance: performance-releated messages
  • queries: executed AQL queries, slow queries
  • replication: replication-related info
  • requests: HTTP requests
  • startup: information about server startup and shutdown
  • threads: information about threads

Log outputs

The log option --log.output <definition> allows directing the global or per-topic log output to different outputs. The output definition <definition> can be one of

  • - for stdin
  • + for stderr
  • syslog://<syslog-facility>
  • syslog://<syslog-facility>/<application-name>
  • file://<relative-path>

The option can be specified multiple times in order to configure the output for different log topics. To set up a per-topic output configuration, use --log.output <topic>=<definition>, e.g.


logs all queries to the file “queries.txt”.

The old option --log.file is still available in 3.0 for convenience reasons. In 3.0 it is a shortcut for the more general option --log.output file://filename.

The old option --log.requests-file is still available in 3.0. It is now a shortcut for the more general option --log.output requests=file://....

Using --log.output also allows directing log output to different files based on topics. For example, to log all AQL queries to a file “queries.log” one can use the options:

--log.level queries=trace --log.output queries=file:///path/to/queries.log

To additionally log HTTP request to a file named “requests.log” add the options:

--log.level requests=info --log.output requests=file:///path/to/requests.log

Forcing direct output

The option --log.force-direct can be used to disable logging in an extra logging thread. If set to true, any log messages are immediately printed in the thread that triggered the log message. This is non-optimal for performance but can aid debugging. If set to false, log messages are handed off to an extra logging thread, which asynchronously writes the log messages.

Local time

Log dates and times in local time zone: --log.use-local-time

If specified, all dates and times in log messages will use the server’s local time-zone. If not specified, all dates and times in log messages will be printed in UTC / Zulu time. The date and time format used in logs is always YYYY-MM-DD HH:MM:SS, regardless of this setting. If UTC time is used, a Z will be appended to indicate Zulu time.

Line number

Log line number: --log.line-number

Normally, if an human readable fatal, error, warning or info message is logged, no information about the file and line number is provided. The file and line number is only logged for debug and trace message. This option can be use to always log these pieces of information.


Log prefix: --log.prefix prefix

This option is used specify an prefix to logged text.


Log thread identifier: --log.thread

Whenever log output is generated, the process ID is written as part of the log information. Setting this option appends the thread id of the calling thread to the process id. For example,

2010-09-20T13:04:01Z [19355] INFO ready for business

when no thread is logged and

2010-09-20T13:04:17Z [19371-18446744072487317056] ready for business

when this command line option is set.


Log role: --log.role

When set to true, this option will make the ArangoDB logger print a single character with the server’s role into each logged message. The roles are:

  • U: undefined/unclear (used at startup)
  • S: single server
  • C: coordinator
  • P: primary
  • A: agent

The default value for this option is false, so no roles will be logged.