top Command

1. What Is top?

top is a terminal-based program that displays dynamic, real-time information about system activity. It helps system administrators identify high-resource processes and monitor overall system health.

2. Running top

Usually preinstalled in most Linux distributions, you can launch it with:

top

3. Basic top Output

• uptime: Duration the system has been running
• load average: System load over the past 1, 5, and 15 minutes
• Tasks: Total number of processes (running, sleeping, stopped)
• CPU usage: Percent CPU used by user/system/idle
• Memory: RAM usage breakdown
• Swap: Swap memory usage

4. Interactive Control Keys

Key	Function
h	Display help screen
k	Kill a process (enter PID)
r	Renice a process
u	Filter by user
n / #	Set number of processes to show
q	Quit top

5. Useful Command-Line Options

• -d: Refresh interval in seconds

top -d 3

• -u: Show processes by specific user

top -u jina

• -p: Show specific process IDs

top -p 1234,5678

6. Sorting Within top

• P – Sort by CPU usage
• M – Sort by memory usage
• T – Sort by time running

7. Enhanced Alternative: htop

htop offers a more user-friendly and graphical interface:

sudo apt install htop

htop

8. Practical Use Cases

• Identify CPU-intensive processes
• Monitor RAM usage trends
• Kill or renice unresponsive processes
• Investigate system slowdowns

9. Conclusion

top is a foundational Linux tool for understanding what’s consuming system resources in real time. With its keyboard shortcuts and configurable options, it empowers administrators to detect performance bottlenecks and manage processes effectively.