arthas/en/_sources/faq.md.txt

## FAQ


> For questions that are not in this list, please search in issues. [https://github.com/alibaba/arthas/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](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](quick-start.md).


##### 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:

```bash
options unsafe true
```

See more at [options](options.md)


##### How to view the result in `json` format

```bash
options json-format true
```

See more at [options](options.md)


##### 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](advice-class.md) 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](https://github.com/alibaba/arthas/issues/1348)

example [arthas-demo](quick-start.md)

```bash
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?

```bash
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](https://github.com/alibaba/arthas/issues/1141), V8.1.0 or above is compatible, refer to skywalking configuration for more details. [skywalking compatible with other javaagent bytecode processing](https://github.com/apache/skywalking/blob/v8.1.0/docs/en/FAQ/Compatible-with-other-javaagent-bytecode-processing.md).