druid/docs/configuration/logging.md

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---
id: logging
title: "Logging"
---
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Apache Druid processes will emit logs that are useful for debugging to log files.
These processes also emit periodic [metrics](../configuration/index.md#enabling-metrics) about their state.
Metric info logs can be disabled with `-Ddruid.emitter.logging.logLevel=debug`.
Druid uses [log4j2](http://logging.apache.org/log4j/2.x/) for logging.
The default configuration file log4j2.xml ships with Druid under conf/druid/{config}/_common/log4j2.xml .
By default, Druid uses `RollingRandomAccessFile` for rollover daily, and keeps log files up to 7 days.
If that's not suitable in your case, you could modify the log4j2.xml to meet your need.
An example log4j2.xml file is shown below:
```
<?xml version="1.0" encoding="UTF-8" ?>
<Configuration status="WARN">
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{ISO8601} %p [%t] %c - %m%n"/>
</Console>
<RollingRandomAccessFile name="FileAppender"
fileName="${sys:druid.log.path}/${sys:druid.node.type}.log"
filePattern="${sys:druid.log.path}/${sys:druid.node.type}.%d{yyyyMMdd}.log">
<PatternLayout pattern="%d{ISO8601} %p [%t] %c - %m%n"/>
<Policies>
<TimeBasedTriggeringPolicy interval="1" modulate="true"/>
</Policies>
<DefaultRolloverStrategy>
<Delete basePath="${sys:druid.log.path}/" maxDepth="1">
<IfFileName glob="*.log" />
<IfLastModified age="7d" />
</Delete>
</DefaultRolloverStrategy>
</RollingRandomAccessFile>
<Loggers>
<Root level="info">
<AppenderRef ref="FileAppender"/>
</Root>
<!-- Uncomment to enable logging of all HTTP requests
<Logger name="org.apache.druid.jetty.RequestLog" additivity="false" level="DEBUG">
<AppenderRef ref="FileAppender"/>
</Logger>
-->
</Loggers>
</Configuration>
```
> NOTE:
> Although the log4j configuration file is shared with Druid's peon processes,
> the appenders in this file DO NOT take effect for peon processes for they always output logs to console.
> And middle managers are responsible to redirect the console output to task log files.
>
> But the logging levels settings take effect for these peon processes
> which means you can still configure loggers at different logging level for peon processes in this file.
>
## How to change log directory
By default, Druid outputs the logs to a directory `log` under the directory where Druid is launched from.
For example, if Druid is started from its `bin` directory, there will be a subdirectory `log` generated under `bin` directory to hold the log files.
If you want to change the log directory, set environment variable `DRUID_LOG_DIR` to the right directory before you start Druid.
## My logs are really chatty, can I set them to asynchronously write?
Yes, using a `log4j2.xml` similar to the following causes some of the more chatty classes to write asynchronously:
```
<?xml version="1.0" encoding="UTF-8" ?>
<Configuration status="WARN">
<Appenders>
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{ISO8601} %p [%t] %c - %m%n"/>
</Console>
</Appenders>
<Loggers>
<!-- AsyncLogger instead of Logger -->
<AsyncLogger name="org.apache.druid.curator.inventory.CuratorInventoryManager" level="debug" additivity="false">
<AppenderRef ref="Console"/>
</AsyncLogger>
<AsyncLogger name="org.apache.druid.client.BatchServerInventoryView" level="debug" additivity="false">
<AppenderRef ref="Console"/>
</AsyncLogger>
<!-- Make extra sure nobody adds logs in a bad way that can hurt performance -->
<AsyncLogger name="org.apache.druid.client.ServerInventoryView" level="debug" additivity="false">
<AppenderRef ref="Console"/>
</AsyncLogger>
<AsyncLogger name ="org.apache.druid.java.util.http.client.pool.ChannelResourceFactory" level="info" additivity="false">
<AppenderRef ref="Console"/>
</AsyncLogger>
<Root level="info">
<AppenderRef ref="Console"/>
</Root>
</Loggers>
</Configuration>
```