FAQ

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

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

https://github.com/alibaba/arthas/issues/44

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 arthas-demo in quick-start.

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

By default, classes beginning with java. are filtered out, but they can be turned on:

options unsafe true

See more at options

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?

No. But 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/1348

example arthas-demo

watch demo.MathGame primeFactors traceE '{params,returnObj,throwExp}' -v -n 5 -x 3 'params.length >0 && returnObj instanceof java.util.List'

How to watch or trace constructor?

watch demo.MathGame <init> '{params,returnObj,throwExp}' -v -n 5 -x 3 '1==1'

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 agent, V8.1.0 or above is compatible, refer to skywalking configuration for more details. skywalking compatible with other javaagent bytecode processing.

Can I use arthas offline?

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