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Chapter 6: Process Management

Overview

In Linux, processes are instances of running programs. Process management is essential for monitoring system performance, debugging, and ensuring the stability of the operating system. This chapter covers the tools and commands for viewing, managing, and controlling processes.

1. Understanding Linux Processes

Key Concepts:

  • Process ID (PID): A unique identifier assigned to each process.
  • Parent Process ID (PPID): The ID of the process that created the current process.
  • Foreground Processes: Processes that run interactively in the terminal.
  • Background Processes: Processes that run without user interaction.
  • Daemon: A background service typically started at boot time.

Process States:

  • Running: The process is currently executing.
  • Sleeping: The process is waiting for a resource.
  • Stopped: The process has been stopped by a signal.
  • Zombie: The process has completed but is not yet removed by its parent.

2. Viewing Processes

ps: Process Snapshot

  • Displays information about running processes.

Examples:

ps aux                # Show all processes with detailed information
ps -ef                # Show all processes in full format

top: Real-Time Process Monitoring

  • Interactive tool for viewing and managing processes in real-time.

Usage:

top
  • Common Keys in top:
    • q: Quit
    • k: Kill a process
    • r: Renice a process

htop: Enhanced Process Viewer

  • Provides a user-friendly interface for process management.

Installation:

sudo apt install htop

Usage:

htop

3. Managing Processes

kill: Terminate a Process

  • Sends a signal to a process to terminate it.

Syntax:

kill [signal] PID

Examples:

  • Terminate a process: 
    kill 1234
  • Forcefully kill a process: 
    kill -9 1234

pkill: Kill Processes by Name

  • Terminates processes matching a pattern.

Example:

pkill firefox

jobs: List Background Jobs

  • Displays jobs started in the current session.

Example:

jobs

fg and bg: Foreground and Background Processes

  • fg: Bring a background process to the foreground.
  • bg: Resume a stopped process in the background.

Example:

fg %1
bg %2

4. Prioritizing Processes

nice: Set Process Priority

  • Assigns a priority to a process when starting it.
  • Priority ranges from -20 (highest) to 19 (lowest).

Example:

nice -n 10 ./script.sh

renice: Change Process Priority

  • Adjusts the priority of a running process.

Example:

sudo renice -5 1234

5. Monitoring Resource Usage

vmstat: Virtual Memory Statistics

  • Provides an overview of system performance.

Example:

vmstat 2 5

iostat: CPU and Disk I/O Statistics

  • Displays CPU and I/O usage.

Example:

iostat

free: Memory Usage

  • Shows free and used memory.

Example:

free -h

6. Advanced Process Management

strace: Trace System Calls

  • Debugs a process by tracing its system calls and signals.

Example:

strace -p 1234

lsof: List Open Files

  • Shows files opened by processes.

Example:

lsof -p 1234

systemctl: Manage System Services

  • Controls services and daemons.

Examples:

  • Start a service: 
    sudo systemctl start apache2
  • Stop a service: 
    sudo systemctl stop apache2
  • Check service status: 
    sudo systemctl status apache2

Summary

By the end of this chapter, you should be able to:

  • View and monitor processes using ps, top, and htop.
  • Manage processes with kill, pkill, fg, and bg.
  • Adjust process priorities using nice and renice.
  • Debug and analyze processes with strace and lsof.

Next Steps:

Exercises

  1. List all processes running on your system and identify their PIDs.
  2. Start a process in the background and bring it to the foreground using fg.
  3. Change the priority of a running process using renice.
  4. Use strace to debug a simple script and analyze its system calls.
  5. Monitor memory and CPU usage on your system using vmstat and iostat.