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Arthas Quick Start Guide

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🛠️ Arthas Introduction

Arthas is a powerful Java diagnostic tool open-sourced by Alibaba in September 2018. It supports JDK 6 and above, provides interactive command-line mode, supports multiple platforms (Linux/Mac/Windows), and features Tab auto-completion. Arthas helps developers quickly diagnose and locate Java application production issues without modifying code or restarting services.

🤔 Why Do We Need Arthas?

In daily development, when encountering the following Java issues, traditional methods are inefficient:

  • CPU load spikes, but unable to locate specific threads
  • Thread deadlocks causing system freeze, difficult to view thread status in real-time
  • Application response becomes slow, method call chain unclear
  • Suspicion of online code inconsistency with local environment
  • Unable to debug online issues, can only check logs

Arthas provides powerful solutions for these scenarios.

🚀 Quick Start

Installation

Download and run with a single command:

# Download arthas-boot.jar
curl -O https://arthas.aliyun.com/arthas-boot.jar

# Launch Arthas
java -jar arthas-boot.jar

Selecting Target Process

After startup, Arthas will automatically detect all Java processes on the current machine:

[INFO] arthas-boot version: 3.x.x
[INFO] Process:
* [1]: 35542 (Spring Boot Application)
  [2]: 71560 (Tomcat Application)
  [3]: 63914 (Other Java Process)
Please choose the target process (1-3, default is 1):

Simply enter the number to attach to the target process.

🎯 Core Commands

1. Thread Analysis Commands

thread - View Thread Information

View all threads:

[arthas@35542]$ thread

Find high CPU consumption threads:

[arthas@35542]$ thread -n 3
# Shows top 3 threads with highest CPU usage

View specific thread:

[arthas@35542]$ thread 1
# View thread with ID 1

Detect deadlocks:

[arthas@35542]$ thread -b
# Shows blocked threads and potential deadlocks

2. Class and Method Analysis

sc - View Class Information

Search for classes:

[arthas@35542]$ sc *UserService*
# Search for all classes containing 'UserService'

View class details:

[arthas@35542]$ sc -d com.example.UserService
# View detailed information about UserService class

sm - View Method Information

View class methods:

[arthas@35542]$ sm com.example.UserService
# List all methods in UserService class

View method details:

[arthas@35542]$ sm -d com.example.UserService getUserById
# View detailed information about getUserById method

3. Method Monitoring Commands

watch - Monitor Method Execution

Monitor method parameters and return values:

[arthas@35542]$ watch com.example.UserService getUserById '{params, returnObj}' -x 2

Monitor method execution time:

[arthas@35542]$ watch com.example.UserService getUserById '{params, returnObj, throwExp}' -x 2 -b -s -e
# -b: before method execution
# -s: after successful execution
# -e: after exception thrown

trace - Method Call Trace

Trace method execution path:

[arthas@35542]$ trace com.example.UserService getUserById

Trace with time threshold:

[arthas@35542]$ trace com.example.UserService getUserById '#cost > 100'
# Only show calls that take more than 100ms

monitor - Method Execution Statistics

Monitor method execution statistics:

[arthas@35542]$ monitor -c 5 com.example.UserService getUserById
# Monitor for 5 seconds and show statistics

4. JVM Analysis Commands

dashboard - System Overview

[arthas@35542]$ dashboard
# Real-time display of system metrics: CPU, memory, GC, threads, etc.

jvm - JVM Information

[arthas@35542]$ jvm
# View JVM version, parameters, memory allocation, etc.

memory - Memory Information

[arthas@35542]$ memory
# View heap/non-heap memory usage details

gc - GC Information

[arthas@35542]$ gc
# View garbage collection statistics

5. Class Loading Commands

classloader - View ClassLoader Information

[arthas@35542]$ classloader
# View all ClassLoader information

Find classes loaded by specific ClassLoader:

[arthas@35542]$ classloader -c 327a647b
# View classes loaded by specified ClassLoader

mc and redefine - Hot Code Replacement

Compile Java source:

[arthas@35542]$ mc /tmp/UserService.java -d /tmp
# Compile UserService.java to /tmp directory

Hot replace class:

[arthas@35542]$ redefine /tmp/com/example/UserService.class
# Hot replace UserService class

🌐 Web Console

Arthas also provides a Web interface for easier use:

# Start with Web Console
java -jar arthas-boot.jar --target-ip 0.0.0.0

Then access http://localhost:8563 in your browser.

📊 Practical Troubleshooting Examples

Example 1: Troubleshooting High CPU Issues

# Step 1: View high CPU threads
[arthas@35542]$ thread -n 5

# Step 2: View specific thread details
[arthas@35542]$ thread 42

# Step 3: Trace suspected methods
[arthas@35542]$ trace com.example.service.ProcessService process

Example 2: Method Performance Analysis

# Monitor method execution time
[arthas@35542]$ watch com.example.UserService getUserById '{params[0], returnObj, cost}' -x 2

# Trace method call chain
[arthas@35542]$ trace com.example.UserService getUserById '#cost > 50'

Example 3: Deadlock Detection

# Detect deadlocks
[arthas@35542]$ thread -b

# View blocked thread details
[arthas@35542]$ thread 28

Example 4: Memory Leak Investigation

# Monitor GC situation
[arthas@35542]$ gc

# View heap memory details
[arthas@35542]$ memory

# Monitor object creation
[arthas@35542]$ watch java.util.ArrayList <init> '{params, target}' -x 2

⚠️ Production Environment Considerations

Performance Impact

  1. Minimal Impact: Arthas has very low performance overhead under normal use
  2. Heavy Commands: Commands like watch, trace may have some impact
  3. Recommended: Test in staging environment first

Security Considerations

# Set access restrictions
java -jar arthas-boot.jar --target-ip 127.0.0.1 --http-port 8563 --telnet-port 3658

Resource Management

# Exit Arthas
[arthas@35542]$ quit

# Stop Arthas completely
[arthas@35542]$ stop

🎁 Advanced Features

Profiler Integration

# Start profiler
[arthas@35542]$ profiler start

# Generate flame graph
[arthas@35542]$ profiler getSamples
[arthas@35542]$ profiler status

Log Monitoring

# Monitor log output
[arthas@35542]$ logger

# Change log level
[arthas@35542]$ logger --name com.example --level DEBUG

OGNL Expression Support

# Use OGNL expressions in watch command
[arthas@35542]$ watch com.example.UserService getUserById '@user.name'

# Get static field value
[arthas@35542]$ ognl '@com.example.Constants@DEFAULT_SIZE'

📝 Best Practices

1. Effective Use of Filtering

# Filter by execution time
[arthas@35542]$ trace com.example.UserService * '#cost > 100'

# Filter by parameter values
[arthas@35542]$ watch com.example.UserService getUserById 'params[0] > 1000'

2. Batch Operations

# Monitor multiple methods
[arthas@35542]$ monitor -c 10 com.example.UserService *

3. Result Export

# Export results to file
[arthas@35542]$ trace com.example.UserService getUserById > /tmp/trace.log

🔚 Summary

Arthas is a powerful Java diagnostic tool that can help developers:

  • Quickly locate high CPU and performance issues
  • Real-time monitor method execution without code changes
  • Analyze class loading and memory issues
  • Hot replace code for rapid debugging

Key Points:

  • ✅ Zero intrusion, no need to restart applications
  • ✅ Rich command set covering various diagnostic scenarios
  • ✅ Simple to use with Tab completion support
  • ⚠️ Use cautiously in production, pay attention to performance impact

Arthas is an essential tool for Java developers, especially valuable for production environment troubleshooting and performance optimization.

Performance Tuning Diagnostic Tools Java