UNIX Processes Overview

Study Notes

Process in UNIX

A process is an independent entity that executes a program, initiated when an application is launched, a program is run, or a command is executed.
It is a dynamic entity that can be in one of several states during its lifetime.
Each process has its own memory space, program counter, stack, and set of resources allocated by the operating system.

Process Characteristics

Processes can run concurrently, allowing multiple programs to execute simultaneously.
Each program or command in Linux creates only one process.
An application can initiate multiple processes to fulfill different tasks.

Process Creation

Processes are often created by forking off from an existing process known as the parent process.

Example Scenario

A user opens a text editor application to write a document while also listening to music using a media player.
The text editor and media player are separate processes running concurrently on the operating system.
Each process has its own memory space and resources, allowing them to execute independently of each other.

Types of Processes in UNIX

Foreground Processes

Interactive processes that run in the foreground and interact directly with the user through the terminal.
Examples include text editors, command-line utilities, and interactive programs.

Background Processes

Non-interactive processes that run in the background without requiring direct user interaction.
Examples include batch jobs, automated scripts, and system maintenance tasks.

System Processes

Essential processes that are initiated and managed by the operating system to perform system-level tasks.
Examples include kernel processes, daemons, and system services.

User Processes

Processes initiated and managed by users to perform specific tasks or run applications.
Can be interactive or non-interactive and may run in the foreground or background.

Daemon Processes

Background processes that run continuously and perform specific system tasks or services.
Examples include network services (e.g., web server, DNS server), logging, printing, and scheduling tasks.

Parent and Child Processes

Parent processes are processes that initiate the creation of other processes, known as child processes.
Child processes inherit attributes from their parent processes and may perform tasks independently or in coordination with the parent.

Zombie and Orphan Process

A zombie process is a Linux process that has finished its execution but still has an entry in the process table.
Zombie processes usually get created when a child process completes its execution but the parent process has not acknowledged its termination.

Description

Learn about processes in UNIX, which are independent entities that execute programs. Processes have different states during their lifetime, each having its own memory space, program counter, stack, and allocated resources. They can run concurrently, enabling multiple programs to execute simultaneously.