arthasv3.7.2
Table of Contents

FAQ

TIP

For questions that are not in this list, please search in issues. https://github.com/alibaba/arthas/issuesopen in new window

Where is the log file?

Log file path: ~/logs/arthas/arthas.log

How much impact does Arthas attach have on the performance of the original process?

https://github.com/alibaba/arthas/issues/44open in new window

target process not responding or HotSpot VM not loaded

com.sun.tools.attach.AttachNotSupportedException: Unable to open socket file: target process not responding or HotSpot VM not loaded

  1. Check whether the current user and the target java process are consistent. If they are inconsistent, switch to the same user. JVM can only attach java processes under the same user.
  2. Try to use jstack -l $pid. If the process does not respond, it means that the process may freeze and fail to respond to the JVM attach signal. So Arthas based on the attach mechanism cannot work. Try to use jmap heapdump to analyze.
  3. Try to attach math-game in quick-start.
  4. For more information: https://github.com/alibaba/arthas/issues/347open in new window

Can commands such as trace/watch enhance the classes in jdk?

By default, classes beginning with java. or the classes loaded by the Bootstrap ClassLoader are filtered out, but they can be turned on:

options unsafe true

See more at options

TIP

To support the jars appended by java.lang.instrument.Instrumentation#appendToBootstrapClassLoaderSearch need to enable unsafe.

How to view the result in json format

options json-format true

See more at options

Can arthas trace native methods

No.

Can arthas view the value of a variable in memory?

  1. You can use vmtool command.
  2. You can use some tricks to intercept the object with the tt command, or fetch it from a static method.

How to filter method with the same name?

You can used all variables in fundamental fields in expressions for the condition express to filter method with the same name, you can use the number of parameters params.length ==1,parameter type params[0] instanceof java.lang.Integer,return value type returnObj instanceof java.util.List and so on in one or more combinations as condition express.

You can use -v to view the condition express result https://github.com/alibaba/arthas/issues/1348open in new window

example math-game

watch demo.MathGame primeFactors '{params,returnObj,throwExp}' 'params.length >0 && returnObj instanceof java.util.List' -v

How to watch or trace constructor?

watch demo.MathGame <init> '{params,returnObj,throwExp}' -v

How to watch or trace inner classes?

In the JVM specification the name of inner classes is OuterClass$InnerClass.

watch OuterClass$InnerClass

Enter Unicode characters

Convert Unicode characters to \u representation:

ognl '@java.lang.System@out.println("Hello \u4e2d\u6587")'

java.lang.ClassFormatError: null, skywalking arthas compatible use

When error log appear java.lang.ClassFormatError: null, it is usually modified by other bytecode tools that are not compatible with arthas modified bytecode.

For example: use skywalking V8.1.0 below cannot trace, watch classes enhanced by skywalking agentopen in new window, V8.1.0 or above is compatible, refer to skywalking configuration for more details. skywalking compatible with other javaagent bytecode processingopen in new window.

class redefinition failed: attempted to change the schema (add/remove fields)

Reference: https://github.com/alibaba/arthas/issues/2165open in new window

Can I use arthas offline?

Yes. Just download the full size package and unzip it, refer to: Download.

Attach the process with pid 1 in docker/k8s failed

Reference: https://github.com/alibaba/arthas/issues/362#issuecomment-448185416open in new window

Why is the new version of Arthas downloaded, but the old version is connected?

For example, the started version of as.sh/arthas-boot.jar is 3.5., but after connecting, the printed arthas version is 3.4..

It may be that the target process has been diagnosed with the old version of arthas before. You can execute stop to stop the old version of arthas, and then reuse the new version to attach.