ArangoDB Server Log Options

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:

[log]
level = startup=trace
level = queries=trace
level = info

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.

See Log Levels in the Monitoring chapter for a detailed description of the different levels.

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-related 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

See more log levels

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.

queries=file://queries.txt

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

Any occurrence of $PID inside a log output value will be replaced at runtime with the actual process id. This enables logging to process-specific files, e.g.

--log.output 'file:///var/log/arangod.log.$PID'

Please note that the dollar sign may need extra escaping when specified from inside shells such as Bash.

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

If you specify --log.file-mode octalvalue then any newly created log file will use “octalvalue” as file mode. Please note that the umask value will be applied as well.

If you specify --log.file-group name then any newly created log file will try to use “name” as group name. Please note that you have to be a member of that group. Otherwise the group ownership will not be changed. Please note that this option is only available under Linux and Mac. It is not available under Windows.

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.

Time format

The option --log.time-format controls the time format used in log output. The possible values for this option are:

Escaping

There are two flags for retaining or escaping control and Unicode characters in the log. The flag --log.escape is deprecated since v3.9.0, and instead, the new flags --log.escape-control-chars and log.escape-unicode-chars should be used.

• --log.escape-control-chars:

  This flag applies to the control characters, that have hex codes below \x20, and also the character DEL with hex code \x7f.

  When the flag value is set to false, control characters will be retained when they have a visible representation, and replaced with a space character in case they do not have a visible representation. For example, the control character \n is visible, so a \n will be displayed in the log. Contrary, the control character BEL is not visible, so a space will be displayed instead.

  When the flag value is set to true, the hex code for the character is displayed, for example, the BEL character will be displayed as its hex code, \x07.

  The default value for this flag is true to ensure compatibility with previous versions.

• --log.escape-unicode-chars:

  If its value is set to false, Unicode characters will be retained and written to the log as-is. For example, 犬 will be logged as 犬. If the flag value is set to true, any Unicode characters are escaped, and the hex codes for all Unicode characters are logged instead. For example, 犬 would be logged as its hex code, \u72AC.

  The default value for this flag is set to false for compatibility with previous versions.

A side effect of turning off the escaping is that it will reduce the CPU overhead for the logging. However, this will only be noticeable when logging is set to a very verbose level (e.g. debug or trace).

Maximum line length

Introduced in: v3.7.9

--log.max-entry-length value

This option can be used to limit the maximum line length for individual log messages that are written into normal logfiles by arangod.

Any log messages longer than the specified value will be truncated and the suffix ... will be added to them.

The purpose of this parameter is to shorten long log messages in case there is lot a lot of space for logfiles, and to keep rogue log messages from overusing resources.

The default value is 128 MB, which is very high and should effectively mean downwards-compatibility with previous arangod versions, which did not restrict the maximum size of log messages.

Color logging

--log.color value

Logging to terminal output is by default colored. Colorful logging can be turned off by setting the value to false.

Source function, file and line number

--log.line-number

If enabled, then log messages will include the function name, file name and line number of the source code that issued the log message. The format is func@FileName.cpp:123.

Example:

2021-06-08T16:09:31Z [1] INFO [prepare@GreetingsFeature.cpp:43] [e52b0] ArangoDB 3.7.11 [linux] 64bit, using jemalloc, build tags/v3.7.11-0-g5ca39c161b, VPack 0.1.33, RocksDB 6.8.0, ICU 64.2, V8 7.9.317, OpenSSL 1.1.1k  25 Mar 2021
2021-06-08T16:09:31Z [1] INFO [prepare@EnvironmentFeature.cpp:68] [75ddc] detected operating system: Linux version 4.15.0-140-generic (buildd@lgw01-amd64-054) (gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)) #144-Ubuntu SMP Fri Mar 19 14:12:35 UTC 2021
2021-06-08T16:09:31Z [1] INFO [prepare@EnvironmentFeature.cpp:251] [25362] {memory} Available physical memory: 67513589760 bytes, available cores: 32
2021-06-08T16:09:31Z [1] WARNING [prepare@EnvironmentFeature.cpp:426] [3e451] {memory} It is recommended to set NUMA to interleaved.
2021-06-08T16:09:31Z [1] WARNING [prepare@EnvironmentFeature.cpp:428] [b25a4] {memory} put 'numactl --interleave=all' in front of your command
2021-06-08T16:09:31Z [1] INFO [prepare@AuthenticationFeature.cpp:190] [43396] {authentication} Jwt secret not specified, generating...
2021-06-08T16:09:31Z [1] INFO [prepare@EngineSelectorFeature.cpp:187] [144fe] using storage engine 'rocksdb'
2021-06-08T16:09:31Z [1] INFO [reportRole@ClusterFeature.cpp:410] [3bb7d] {cluster} Starting up with role SINGLE
2021-06-08T16:09:31Z [1] INFO [start@FileDescriptorsFeature.cpp:90] [a1c60] {syscall} file-descriptors (nofiles) hard limit is 1048576, soft limit is 1048576
2021-06-08T16:09:31Z [1] INFO [start@AuthenticationFeature.cpp:222] [3844e] {authentication} Authentication is turned off, authentication for unix sockets is turned on
2021-06-08T16:09:32Z [1] INFO [start@IResearchFeature.cpp:972] [c1b63] {arangosearch} ArangoSearch maintenance: [5..5] commit thread(s), [5..5] consolidation thread(s)
2021-06-08T16:09:32Z [1] INFO [dump@EndpointList.cpp:222] [6ea38] using endpoint 'http+tcp://0.0.0.0:8529' for non-encrypted requests
2021-06-08T16:09:32Z [1] INFO [start@BootstrapFeature.cpp:370] [cf3f4] ArangoDB (version 3.7.11 [linux]) is ready for business. Have fun!

Prefix

Log prefix: --log.prefix

This option specifies a prefix for log messages.

Example: arangod ... --log.prefix "-->"

2020-07-23T09:46:03Z --> [17493] INFO ...

Process ID, Thread ID and Name

Log Process identifier: --log.process (introduced in 3.8.0)

Log thread identifier: --log.thread

Log thread name: --log.thread-name

When log output is generated, the process ID is emitted as part of the log information by default. This can be turned off by adjusting the --log.process option.

The thread ID is not emitted by default, but it can be enabled by setting the option --log.thread.

To also log thread names, it is possible to set the --log.thread-name option. By default --log.thread-name is set to false.

Here is an example that only contains the process ID (19355 in this case):

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

And here is an example that also contains the thread ID in addition:

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

And another example with process and thread identifier logging disabled, but thread name logging turned on:

2010-09-20T13:04:29Z [main] ... ready for business

IDs

Log IDs: --log.ids true

Since ArangoDB 3.5, each log invocation in the ArangoDB source code contains a unique log ID, which can be used to quickly find the location in the source code that produced a specific log message. These log IDs are shown by default, unless the option --log.ids is set to false.

Log IDs are printed as 5-digit hexadecimal identifiers in square brackets between the log level and the log topic, e.g.

2020-06-22T21:16:48Z [39028] INFO [144fe] {general} using storage engine 'rocksdb'

(where 144fe is the log ID).

Role

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 / DB-Server
• A: Agent

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

Hostname

Log hostname: --log.hostname

This option specifies an optional hostname to be logged at the beginning of each log message (for regular logging) or inside the hostname attribute (for JSON-based logging).

The default value is the empty string, meaning no hostnames will be logged. Setting this option to a value of auto will automatically determine the hostname and use that value.

Example: arangod ... --log.hostname "auto"

JSON log output

Introduced in: v3.8.0

Toggle JSON log output: --log.use-json-format

This option can be used to switch log output to JSON format. Each log message then produces a separate line with JSON-encoded log data, which can be consumed by applications.

The attributes produced for each log message JSON object are:

Log API Access

Introduced in: v3.4.11, v3.5.6, v3.6.5, v3.7.1

/_admin/log control: --log.api-enabled

Credentials data is not written to log files. Nevertheless, some logged data might be sensitive depending on the context of the deployment. For example, if request logging is switched on, user requests and corresponding data might end up in log files. Therefore, a certain care with log files is recommended.

Since the database server offers an API to control logging and query logging data, this API has to be secured properly. By default, the API is accessible for admin users (administrative access to the _system database). However, one can lock this down further.

The possible values for this option are:

• true: The API /_admin/log is accessible for admin users.
• jwt: The API /_admin/log is accessible only for the superuser (authentication with JWT token and empty username).
• false: The API /_admin/log is not accessible at all.

The default value is true.

Logging to memory buffers

Introduced in: v3.8.0

Log to memory: --log.in-memory

This option can be used to toggle storing log messages in memory, from which they can be consumed via the /_admin/log HTTP API and via the Web UI. By default, this option is turned on, so log messages are consumable via the API and UI. Turning this option off will disable that functionality, save a tiny bit of memory for the in-memory log buffers and prevent potential log information leakage via these means.

Log level control for in-memory log messages: --log.in-memory-level

This option can be used to control which log messages are preserved in memory (in case --log.in-memory is set to true). The default value is info, meaning all log messages of types info, warning, error and fatal will be stored by an instance in memory. By setting this option to warning, only warning, error and fatal log messages will be preserved in memory, and by setting the option to error only error and fatal messages will be kept. This option is useful because the number of in-memory log messages is limited to the latest 2048 messages, and these slots are by default shared between informational, warning and error messages.