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Configure logging

Teku uses Log4J2 for logging, and provides multiple methods to configure logging behavior:

The default log directory is OS dependent:

  • macOS: ~/Library/teku/logs
  • Unix/Linux: $XDG_DATA_HOME/teku/logs if $XDG_DATA_HOME is set; otherwise ~/.local/share/teku/logs
  • Windows: %localappdata%\teku\logs

The default Docker image location is /root/.local/share/teku/logs.

Basic log level settings

Use the --logging command line option to specify logging verbosity. The --logging option changes the volume of events displayed in the log. Valid log levels are OFF, FATAL, ERROR, WARN, INFO, DEBUG, TRACE, ALL. The default level is INFO.

By default most logging output is sent to the log file, and limited content shown on the console.


Use the log_level API method to change the log level while Teku is running.

Additional logging options include:

Configure log destination

Use the --log-destination command line option to specify where to output log information. Valid options are BOTH, CONSOLE, DEFAULT_BOTH, FILE. Defaults to DEFAULT_BOTH.

When using BOTH or DEFAULT_BOTH, system updates such as blockchain events are displayed on the console, and errors and other information are logged to a file. Specify the log file with the --log-file command-line option.

Use DEFAULT_BOTH when using a custom Log4J2 configuration file. Any other option applies the custom logging changes on top of its default settings.


For production systems we recommend using the CONSOLE or FILE options to ensure all log information is available in one place.

Advanced custom logging

You can provide your own logging configuration using the standard Log4J2 configuration mechanisms.

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="INFO">
<Property name="root.log.level">INFO</Property>

<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss.SSSZZZ} | %t | %-5level | %c{1} | %msg %throwable%n" />
<Root level="${sys:root.log.level}">
<AppenderRef ref="Console" />

To use your custom configuration, set the environment variable LOG4J_CONFIGURATION_FILE to the location of your configuration file, and ensure --log-destination is not set to DEFAULT_BOTH.

If you have more specific requirements, you can create your own log4j2 configuration.

For Bash-based executions, you can set the variable for only the scope of the program execution by setting it before starting Teku.