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Linux Processes

Understanding Linux processes, process management, and system monitoring.

Linux Processes

A process is a running instance of a program in Linux. This guide explains how processes work, how to manage them, and how to monitor system resources.

Process Basics

What is a Process?

A process is:

  • A running instance of a program
  • Has its own memory space
  • Has a unique Process ID (PID)
  • Can create child processes

Process States

Processes can be in different states:

  1. Running: Currently executing
  2. Waiting: Waiting for an event or resource
  3. Stopped: Suspended by a signal
  4. Zombie: Terminated but not cleaned up
  5. Dead: Terminated and cleaned up

Process Management

Process Commands

ps      # List processes
top     # Display system processes
htop    # Interactive process viewer
kill    # Send signals to processes
nice    # Run with modified priority
renice  # Change process priority

Process Information

Key process information:

  • PID (Process ID)
  • PPID (Parent Process ID)
  • UID (User ID)
  • GID (Group ID)
  • CPU usage
  • Memory usage
  • Start time
  • Command line

Process Control

Signals

Common signals:

  • SIGTERM (15): Graceful termination
  • SIGKILL (9): Force termination
  • SIGSTOP (19): Stop process
  • SIGCONT (18): Continue process
  • SIGHUP (1): Hang up

Process Priority

Linux uses a priority system:

  • Nice values: -20 to +19
  • Lower nice value = higher priority
  • Default nice value: 0

System Monitoring

Resource Monitoring

top     # Real-time system monitoring
vmstat  # Virtual memory statistics
iostat  # I/O statistics
sar     # System activity reporter

Process Monitoring

ps aux  # Detailed process information
lsof    # List open files
strace  # Trace system calls

Process Creation

Fork and Exec

  1. Fork

    • Creates a copy of the current process
    • Child process gets new PID
    • Parent process continues

  2. Exec

    • Replaces current process with new program
    • PID remains the same
    • Memory space is replaced

Daemon Processes

Characteristics:

  • Run in background
  • No controlling terminal
  • Parent process is init (PID 1)
  • Handle system services

Process Communication

IPC Methods

  1. Pipes

    • Named pipes (FIFOs)
    • Anonymous pipes

  2. Shared Memory

    • Fastest IPC method
    • Requires synchronization

  3. Message Queues

    • Structured messages
    • System-wide

  4. Semaphores

    • Synchronization primitives
    • Control access to resources

Best Practices

  1. Process Management

    • Use appropriate signals
    • Clean up zombie processes
    • Monitor resource usage

  2. System Monitoring

    • Regular performance checks
    • Resource usage tracking
    • Process health monitoring

  3. Security

    • Run processes with minimal privileges
    • Monitor for suspicious processes
    • Regular security audits

Next Steps

Continue learning about:

  • Advanced process management
  • System tuning
  • Performance optimization
  • Process debugging
  • Container management
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