Complete Guide to PM2: Theory, Installation & Essential Commands

If you run Node.js applications on a Linux server, you need a process manager that keeps your app running 24/7, restarts automatically on crashes, handles logs, and survives system reboots. PM2 is the most popular tool for that.

This guide covers everything: ✔ What PM2 is ✔ Why developers use it ✔ How to install it ✔ How to start/stop/manage apps ✔ All essential PM2 commands you need daily ✔ Setting up PM2 to run applications on system startup ✔ Advanced ecosystem configuration

What is PM2?

PM2 (Process Manager 2) is a production-grade process manager for Node.js applications. It ensures your app:

• Stays running even after crashes
• Automatically restarts after server reboot
• Runs multiple apps concurrently
• Monitors CPU & RAM usage
• Provides live logs
• Supports zero-downtime reloads

PM2 is widely used in MERN, MEAN, Express.js APIs, Next.js, Vite, and other Node-based applications.

🧠 How PM2 Works (Simple Theory)

PM2 sits between your app and the operating system:

User → PM2 → Node.js App → System

Key responsibilities:

1️⃣ Process Management

PM2 starts your app and keeps it alive. If the app crashes, PM2 restarts it instantly.

2️⃣ Monitoring

PM2 monitors CPU/RAM and gives you live dashboards.

3️⃣ Logging

It merges stdout and stderr logs:

~/.pm2/logs/

4️⃣ Auto-Restart on Boot

PM2 generates a startup script so your app launches after reboot.

5️⃣ Clustering (Optional)

PM2 can run your app in multiple instances to use all CPU cores:

pm2 start app.js -i max

🛠️ Installing PM2

You only need Node.js + npm installed.

Install globally:

npm install -g pm2

Check version:

pm2 -v

You’re ready to use PM2.

🚀 Starting Apps with PM2

Start a Node.js app:

pm2 start app.js

Start with a custom name:

pm2 start app.js --name api

Start an app using an npm script (React, Vite, Next.js, MERN frontend)

pm2 start npm --name frontend -- run dev

Start MERN backend:

pm2 start npm --name backend -- run dev

Start with environment variables:

pm2 start app.js --env production

Start in cluster mode (using all CPU cores):

pm2 start app.js -i max

📌 Essential PM2 Commands (Cheat Sheet)

The most complete list for practical usage:

🔵 Process Management

Start:

pm2 start app.js
pm2 start npm --name frontend -- run dev

Stop:

pm2 stop app
pm2 stop all

Restart:

pm2 restart app
pm2 restart all

Reload (zero-downtime restart for cluster mode):

pm2 reload app

Delete (stop + remove from PM2):

pm2 delete app
pm2 delete all

Pause (stop accepting new connections):

pm2 pause app

Resume:

pm2 resume app

🔵 Monitoring & Logs

List running apps:

pm2 list
pm2 ls

Show process details:

pm2 show app

Detailed info:

pm2 describe app

View logs:

pm2 logs
pm2 logs app

View last 200 lines:

pm2 logs --lines 200

Stream logs in real-time:

pm2 logs --raw

Clear logs:

pm2 flush
pm2 flush app  # specific app

Real-time monitoring dashboard:

pm2 monit

Generate process list in JSON format:

pm2 jlist

Display process metrics:

pm2 show app

🔵 System Startup Configuration

One of PM2’s most powerful features is keeping your applications running after system reboots. Here’s how to set it up:

Step 1: Generate startup script

pm2 startup

This command will output a command you need to run with sudo. Example output:

[PM2] Init System found: systemd
[PM2] To setup the Startup Script, copy/paste the following command:
sudo env PATH=$PATH:/usr/bin /usr/lib/node_modules/pm2/bin/pm2 startup systemd -u yourusername --hp /home/yourusername

Copy and run the command it shows!

Step 2: Save current process list

After starting your applications, save the current PM2 process list:

pm2 save

This creates a dump file at ~/.pm2/dump.pm2

Step 3: Verify startup configuration

Check if startup is configured:

pm2 startup status

Step 4: Update saved processes

If you add or remove applications, save the new configuration:

pm2 save

Step 5: Disable startup (if needed)

pm2 unstartup

Step 6: Manual restoration

If you need to restore saved processes without a reboot:

pm2 resurrect

Important Notes:

1. User-specific: The startup script runs for the specific user who set it up
2. PATH issues: If you get “command not found” after reboot, ensure Node.js is in the system PATH
3. Test reboot: Always test with sudo reboot on a staging server first
4. Multiple users: Each user needs their own PM2 instance and startup configuration

🔵 Cluster Mode

Start in cluster mode with max instances:

pm2 start app.js -i max

Start with specific number of instances:

pm2 start app.js -i 4

Scale up/down cluster:

pm2 scale app +2  # Add 2 instances
pm2 scale app -1  # Remove 1 instance
pm2 scale app 4   # Set to exactly 4 instances

Reload cluster (zero downtime):

pm2 reload app

🔵 Environment Management

Set environment variables:

pm2 start app.js --env production

List environments:

pm2 env

Get environment for specific app:

pm2 show app

Update environment variables:

pm2 restart app --update-env

🔵 Maintenance Commands

Completely kill PM2 daemon:

pm2 kill

Update PM2 to latest version:

pm2 update

Get PM2 version:

pm2 --version

Show PM2 help:

pm2 --help

Generate a sample ecosystem file:

pm2 init

🔵 Advanced Log Management

Disable logging for an app:

pm2 start app.js --no-logs

Merge logs from all instances:

pm2 start app.js --merge-logs

Specify log file location:

pm2 start app.js --log /var/log/myapp.log

Set log file size limit:

pm2 start app.js --max-memory-restart 200M

🎯 Bonus: Use PM2 with an Ecosystem File

For production deployments, use an ecosystem file for better configuration management.

Generate an ecosystem file:

pm2 init

Example ecosystem.config.js (MERN stack):

module.exports = {
  apps: [
    // Backend API (Express.js)
    {
      name: "backend",
      script: "npm",
      args: "run start",
      cwd: "./backend",
      instances: "max",  // Use all CPU cores
      exec_mode: "cluster",
      env: {
        NODE_ENV: "development",
        PORT: 5000,
        MONGODB_URI: "mongodb://localhost:27017/mernapp"
      },
      env_production: {
        NODE_ENV: "production",
        PORT: 5000,
        MONGODB_URI: "mongodb://production-db:27017/mernapp"
      },
      log_date_format: "YYYY-MM-DD HH:mm Z",
      error_file: "/var/log/backend-error.log",
      out_file: "/var/log/backend-out.log",
      merge_logs: true,
      max_memory_restart: "1G",
      watch: false,  // Set to true for development auto-restart
      ignore_watch: ["node_modules", "logs"]
    },
    
    // Frontend (React/Next.js)
    {
      name: "frontend",
      script: "npm",
      args: "run start",
      cwd: "./frontend",
      instances: 1,
      env: {
        NODE_ENV: "development",
        PORT: 3000,
        REACT_APP_API_URL: "http://localhost:5000"
      },
      env_production: {
        NODE_ENV: "production",
        PORT: 3000,
        REACT_APP_API_URL: "https://api.yourdomain.com"
      },
      error_file: "/var/log/frontend-error.log",
      out_file: "/var/log/frontend-out.log",
      max_memory_restart: "512M"
    }
  ]
};

Start all apps from ecosystem file:

pm2 start ecosystem.config.js

Start with production environment:

pm2 start ecosystem.config.js --env production

Stop all apps from ecosystem file:

pm2 stop ecosystem.config.js

Delete all apps from ecosystem file:

pm2 delete ecosystem.config.js

Reload all apps (zero downtime):

pm2 reload ecosystem.config.js

🔧 Common Issues & Solutions

Issue 1: PM2 not starting on reboot

Solution:

# Remove existing startup
pm2 unstartup

# Recreate with correct user
pm2 startup

# Run the displayed command with sudo
# Save current processes
pm2 save

Issue 2: Applications not running after PM2 save

Solution: Ensure paths are absolute in your start commands or ecosystem file.

Issue 3: Permission denied errors

Solution:

# Check PM2 logs
pm2 logs

# Run PM2 with correct permissions
sudo chown -R $USER:$USER ~/.pm2

Issue 4: Environment variables not loading

Solution: Use ecosystem file with env_production section and start with:

pm2 start ecosystem.config.js --env production

Issue 5: Memory leaks causing crashes

Solution: Set memory limits:

pm2 start app.js --max-memory-restart 500M

📊 PM2 Monitoring & Metrics

Install PM2 monitoring module:

pm2 install pm2-logrotate  # Automatically rotate logs
pm2 install pm2-server-monit  # Server monitoring

Setup log rotation (prevents disk space issues):

pm2 set pm2-logrotate:max_size 10M  # Max log file size
pm2 set pm2-logrotate:retain 30     # Keep last 30 files
pm2 set pm2-logrotate:compress true # Compress rotated logs

Monitor key metrics:

# Real-time dashboard
pm2 monit

# Show app metrics
pm2 show app

# Generate metrics in JSON
pm2 jlist

🧾 Summary

PM2 is a must-have tool for running production Node.js applications. It keeps apps alive, handles logs, manages restarts, and offers monitoring — all while being extremely easy to use.

What you learned:

✔ What PM2 is and how it works
✔ How to install PM2 globally
✔ How to manage applications (start, stop, restart, delete)
✔ How to monitor logs and performance
✔ How to configure auto-start on system reboot
✔ How to use ecosystem files for complex setups
✔ How to run applications in cluster mode
✔ How to handle common issues
✔ Every essential PM2 command for daily operations

Pro Tips:

1. Always use ecosystem files for production deployments
2. Set up log rotation to prevent disk space issues
3. Test auto-start configuration on a staging server
4. Use cluster mode for Node.js applications to maximize CPU usage
5. Monitor memory usage and set appropriate limits
6. Save your configuration after any changes with pm2 save

Use this guide as your go-to reference whenever you deploy MERN or Node.js apps to production. With PM2 properly configured, your applications will run reliably 24/7, surviving crashes and system reboots automatically.

📚 Additional Resources

• PM2 Official Documentation
• PM2 GitHub Repository
• Node.js Production Best Practices
• Linux Systemd for Node.js Services

Now you’re equipped to run your Node.js applications in production with confidence! 🚀