Linux top and htop Commands: Real-Time Process Monitoring

The top and htop commands are powerful tools for real-time monitoring and management of running processes in a Linux system. They provide a dynamic, interactive view of system activity, making them essential utilities for DevOps professionals and system administrators.

top Command

Basic Syntax

top [options]

Common Options

• -d: Set update delay interval (in seconds)
• -n: Specify number of iterations
• -p: Monitor specific process IDs
• -u: Monitor processes owned by a specific user
• -o: Sort by a specific column

Usage Examples

# Display top resource-consuming processes
$ top

# Sort by CPU usage
$ top -o %CPU

# Monitor a specific process
$ top -p 1234

# Run top for 5 iterations
$ top -n 5

htop Command

Basic Syntax

htop

Key Features

• Interactive, user-friendly interface
• Customizable columns and sorting
• Process tree view
• Support for mouse interaction
• Advanced filtering and search

Usage Examples

# Launch htop
$ htop

# Sort by memory usage
$ htop -s VIRT

# Filter processes by name
$ htop -u myuser

Common Use Cases

1. Performance Monitoring

   # Identify resource-intensive processes
   $ top -o %CPU
   $ htop
   

2. Process Management

   # Kill a specific process
   $ kill -9 $(top -n1 -o %CPU | grep -E '^\s*[0-9]+' | head -1 | awk '{print $1}')
   

3. System Troubleshooting

   # Monitor system activity in real-time
   $ top -d 1
   $ htop
   

Tips and Tricks

1. Customizing top

   # Change sort order
   $ top -o %MEM
   
   # Specify columns to display
   $ top -o %CPU,%MEM,command
   

2. Automating top

   # Run top for a specific number of iterations
   $ top -n 10 -b > top_output.txt
   

3. Navigating htop

   # Sort by a specific column
   $ htop -s PERCENT_CPU
   
   # Search for a process
   $ htop -s command -f nginx
   

Best Practices

1. Monitor Critical Processes

   # Watch for high CPU/memory usage
   $ top -d 5 -o %CPU,%MEM
   

2. Automate Process Management

   # Restart a service if it crashes
   $ while true; do
       htop | grep -q nginx || /etc/init.d/nginx restart
       sleep 60
   done
   

3. Secure Process Information

   # Restrict access to process details
   $ sudo chmod 750 /proc
   

Common Errors and Solutions

1. Permission Denied

   # Use sudo for restricted processes
   $ sudo top
   $ sudo htop
   

2. Process Not Found

   # Check if process is still running
   $ ps -p 1234
   

3. Incomplete Information

   # Use more detailed options
   $ top -o %CPU,%MEM,command
   

Related Commands

• ps: Process status
• kill: Terminate processes
• pgrep: Find processes by name
• pkill: Kill processes by name
• strace: Trace system calls

Advanced Usage

1. Scripting with top

#!/bin/bash
# Kill processes using excessive CPU
while true; do
    top -bn1 | awk '/^ *[0-9]+/ { if ($9 > 50) print $1 }' | xargs kill -9
    sleep 60
done

2. Monitoring Specific Users

#!/bin/bash
# Monitor processes for a specific user
user="myuser"
while true; do
    echo "Processes for $user:"
    top -u "$user"
    sleep 60
done

3. Integrating with Other Tools

# Use top with grep to find Java processes
top | grep java

# Combine with ps to show detailed process information
top -o %CPU,%MEM,command

The top and htop commands are essential tools for real-time process monitoring and management in a Linux environment. Understanding their usage and capabilities is crucial for DevOps professionals to effectively troubleshoot, optimize, and automate their systems.