📘 Chapter 5 – Process Management (Summary)

Based on Linux System Programming by Robert Love

This chapter covers how Linux manages processes, including their creation, execution, and termination. It introduces key system calls and concepts that underpin multitasking and process control in Unix-like systems.

🧠 Core Concepts

A process is an independent program with its own memory and execution context.
The kernel provides process abstraction to manage concurrency.
Processes are scheduled and isolated using virtual memory and process control blocks (PCBs).

🛠️ Process Creation & Termination

fork() creates a new process (child) by duplicating the calling (parent) process using copy-on-write.
exec() replaces the current process image with a new program.
wait() and waitpid() allow the parent to wait for and collect the child’s exit status.
exit() performs cleanup and exits the process gracefully.
_exit() exits immediately without flushing stdio buffers.

🔍 Signals & Zombies

Zombie processes occur when a child exits but the parent doesn’t read its status with wait().
SIGCHLD is sent to the parent when a child terminates.
The init process (PID 1) will adopt and clean up orphaned children.

👥 Process Hierarchies

Every process has a unique PID and a PPID (parent PID).
Together they form a process tree, starting from init.
Tools like ps, pstree, and /proc are useful for visualizing process hierarchies.

🎯 Process Identifiers & Groups

getpid() returns the process’s ID.
getppid() returns the parent’s ID.
Process groups and sessions enable job control, allowing signals to be sent to multiple related processes.

🧩 Resource Cleanup

On termination, the kernel reclaims:
- Memory
- Open file descriptors
- IPC resources
exit() also triggers:
- atexit() handlers
- Standard I/O flushes
- Potential creation of core dumps (if enabled)

✅ Why This Matters

A strong understanding of process control is essential for:

Writing daemons
Managing background jobs
Building shells or supervisors
Avoiding resource leaks and zombie processes

📚 References

Linux System Programming, 2nd Edition by Robert Love (O'Reilly)
man 2 fork, man 2 execve, man 2 wait, man 2 exit, man 7 signal

This summary is for educational purposes.

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