Day 02: Process Management & Signal Handling

// Objective

To master the Linux Process Lifecycle, understanding how to identify resource-hogging daemons and safely terminate rogue processes using proper UNIX signals.

// Core Monitoring Tools

1. Real-Time Telemetry (top)

The standard dashboard for system load.

• Key Metrics: PID (Process ID), %CPU, %MEM, NI (Niceness/Priority).
• Interactive Commands:
  • k : Kill a process (prompts for PID).
  • u : Filter by user.

2. Advanced Visualization (htop)

A graphical ncurses-based viewer.

• Allows scrolling through the process tree.
• Visual bars for CPU/RAM usage per core.

// Process Discovery (ps)

Understanding the “Process Snapshot” command (ps).

# List EVERY running process on the system
ps aux

# Filter for a specific target (e.g., SSH daemon)
ps aux | grep ssh

• a = all users
• u = user/owner column
• x = processes not attached to a terminal (daemons)

// Termination Protocols (Signals)

In Linux, you don’t “kill” a process; you send it a signal.

Command	Signal Code	Description	Consequence
kill <PID>	SIGTERM (15)	The “Polite” Kill	Asks the process to stop. Allows it to save data and close files.
kill -9 <PID>	SIGKILL (9)	The “Force” Kill	The kernel immediately rips the process from memory. Risk of data corruption.

// Research Note

Always attempt SIGTERM (15) first. Only use SIGKILL (9) if a process is zombie/unresponsive.