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logger
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===
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[`logger` online tutorial](https://arthas.aliyun.com/doc/arthas-tutorials?language=en&id=command-logger)
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> Print the logger information, update the logger level
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### Usage
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#### Print the logger information
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Take the following `logback.xml` as an example:
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<configuration>
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<appender name="APPLICATION" class="ch.qos.logback.core.rolling.RollingFileAppender">
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<file>app.log</file>
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<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
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<fileNamePattern>mylog-%d{yyyy-MM-dd}.%i.txt</fileNamePattern>
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<maxFileSize>100MB</maxFileSize>
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<maxHistory>60</maxHistory>
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<totalSizeCap>2GB</totalSizeCap>
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</rollingPolicy>
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<encoder>
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<pattern>%logger{35} - %msg%n</pattern>
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</encoder>
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</appender>
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<appender name="ASYNC" class="ch.qos.logback.classic.AsyncAppender">
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<appender-ref ref="APPLICATION" />
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</appender>
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<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
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<encoder>
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<pattern>%-4relative [%thread] %-5level %logger{35} - %msg %n
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</pattern>
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<charset>utf8</charset>
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</encoder>
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</appender>
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<root level="INFO">
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<appender-ref ref="CONSOLE" />
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<appender-ref ref="ASYNC" />
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</root>
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</configuration>
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```
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The result of the `logger` command:
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```bash
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[arthas@2062]$ logger
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name ROOT
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class ch.qos.logback.classic.Logger
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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level INFO
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effectiveLevel INFO
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additivity true
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codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
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appenders name CONSOLE
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class ch.qos.logback.core.ConsoleAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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target System.out
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name APPLICATION
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class ch.qos.logback.core.rolling.RollingFileAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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file app.log
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name ASYNC
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class ch.qos.logback.classic.AsyncAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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appenderRef [APPLICATION]
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```
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In the `appenders` section:
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* The target of `CONSOLE` logger is `System.out`
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* `APPLICATION` logger is `RollingFileAppender`, the file is `app.log`
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* `ASYNC` its `appenderRef` is `APPLICATION`, which means asynchronous output to the file
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#### View logger information for the special name
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```bash
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[arthas@2062]$ logger -n org.springframework.web
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name org.springframework.web
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class ch.qos.logback.classic.Logger
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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level null
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effectiveLevel INFO
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additivity true
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codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
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```
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#### View logger information for the special classloader
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Note that the hashcode changes, you need to check the current ClassLoader information first, and extract the hashcode corresponding to the ClassLoader.
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if you use`-c`, you have to manually type hashcode by `-c <hashcode>`.
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```bash
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[arthas@2062]$ logger -c 2a139a55
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name ROOT
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class ch.qos.logback.classic.Logger
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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level DEBUG
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effectiveLevel DEBUG
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additivity true
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codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
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appenders name CONSOLE
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class ch.qos.logback.core.ConsoleAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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target System.out
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name APPLICATION
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class ch.qos.logback.core.rolling.RollingFileAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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file app.log
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name ASYNC
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class ch.qos.logback.classic.AsyncAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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appenderRef [APPLICATION]
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```
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For classloader with only one instance, it can be specified by `--classLoaderClass` using class name, which is more convenient to use.
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`logger --classLoaderClass sun.misc.Launcher$AppClassLoader`
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* PS: Here the classLoaderClass in java 8 is sun.misc.Launcher$AppClassLoader, while in java 11 it's jdk.internal.loader.ClassLoaders$AppClassLoader.
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The value of `--classloaderclass` is the class name of classloader. It can only work when it matches a unique classloader instance. The purpose is to facilitate the input of general commands. However, `-c <hashcode>` is dynamic.
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#### Update logger level
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```bash
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[arthas@2062]$ logger --name ROOT --level debug
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update logger level success.
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```
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#### Speecify classloader to update logger level
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By default，logger command will be executed under SystemClassloader, if the application is a traditional `war`, or using spring boot fat jar, then it needs to specify classloader。
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You can first use `sc -d yourClassName` to check specified classloader hashcode，then specify classloader when updating logger level:
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```bash
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[arthas@2062]$ logger -c 2a139a55 --name ROOT --level debug
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```
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#### View the logger information without appenders
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By default, the `logger` command only prints information about the logger with appenders. If you want to see information about loggers without `appender`, you can use the parameter `--include-no-appender`.
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Note that the output will usually be very long.
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```bash
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[arthas@2062]$ logger --include-no-appender
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name ROOT
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class ch.qos.logback.classic.Logger
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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level DEBUG
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effectiveLevel DEBUG
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additivity true
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codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
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appenders name CONSOLE
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class ch.qos.logback.core.ConsoleAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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target System.out
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name APPLICATION
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class ch.qos.logback.core.rolling.RollingFileAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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file app.log
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name ASYNC
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class ch.qos.logback.classic.AsyncAppender
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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appenderRef [APPLICATION]
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name com
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class ch.qos.logback.classic.Logger
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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level null
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effectiveLevel DEBUG
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additivity true
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codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
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name com.alibaba
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class ch.qos.logback.classic.Logger
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classLoader sun.misc.Launcher$AppClassLoader@2a139a55
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classLoaderHash 2a139a55
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level null
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effectiveLevel DEBUG
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additivity true
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codeSource file:/Users/hengyunabc/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar
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...
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```
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