All configuration files for the various services running on the Linux operating system are stored in one or more text files.
Small, single-purpose programs
Linux offers many different tools that we will work with, which can be combined to work together.
Ability to chain programs together to perform complex tasks
The integration and combination of different tools enable us to carry out many large and complex tasks, such as processing or filtering specific data results.
Avoid captive user interfaces
Linux is designed to work mainly with the shell (or terminal), which gives the user greater control over the operating system.
Configuration data stored in a text file
An example of such a file is the /etc/passwd file, which stores all users registered on the system.
Components
Component
Description
Bootloader
A piece of code that runs to guide the booting process to start the operating system. Parrot Linux uses the GRUB Bootloader.
OS Kernel
The kernel is the main component of an operating system. It manages the resources for system’s I/O devices at the hardware level.
Daemons
Background services are called “daemons” in Linux. Their purpose is to ensure that key functions such as scheduling, printing, and multimedia are working correctly. These small programs load after we booted or log into the computer.
OS Shell
The operating system shell or the command language interpreter (also known as the command line) is the interface between the OS and the user. This interface allows the user to tell the OS what to do. The most commonly used shells are Bash, Tcsh/Csh, Ksh, Zsh, and Fish.
Graphics server
This provides a graphical sub-system (server) called “X” or “X-server” that allows graphical programs to run locally or remotely on the X-windowing system.
Window Manager
Also known as a graphical user interface (GUI). There are many options, including GNOME, KDE, MATE, Unity, and Cinnamon. A desktop environment usually has several applications, including file and web browsers. These allow the user to access and manage the essential and frequently accessed features and services of an operating system.
Utilities
Applications or utilities are programs that perform particular functions for the user or another program.
Linux Architecture
The Linux operating system can be broken down into layers:
Layer
Description
Hardware
Peripheral devices such as the system’s RAM, hard drive, CPU, and others.
Kernel
The core of the Linux operating system whose function is to virtualize and control common computer hardware resources like CPU, allocated memory, accessed data, and others. The kernel gives each process its own virtual resources and prevents/mitigates conflicts between different processes.
Shell
A command-line interface (CLI), also known as a shell that a user can enter commands into to execute the kernel’s functions.
System Utility
Makes available to the user all of the operating system’s functionality.
File System Hierarchy
Path
Description
/
The top-level directory is the root filesystem and contains all of the files required to boot the operating system before other filesystems are mounted as well as the files required to boot the other filesystems. After boot, all of the other filesystems are mounted at standard mount points as subdirectories of the root.
/bin
Contains essential command binaries.
/boot
Consists of the static bootloader, kernel executable, and files required to boot the Linux OS.
/dev
Contains device files to facilitate access to every hardware device attached to the system.
/etc
Local system configuration files. Configuration files for installed applications may be saved here as well.
/home
Each user on the system has a subdirectory here for storage.
/lib
Shared library files that are required for system boot.
/media
External removable media devices such as USB drives are mounted here.
/mnt
Temporary mount point for regular filesystems.
/opt
Optional files such as third-party tools can be saved here.
/root
The home directory for the root user.
/sbin
This directory contains executables used for system administration (binary system files).
/tmp
The operating system and many programs use this directory to store temporary files. This directory is generally cleared upon system boot and may be deleted at other times without any warning.
/usr
Contains executables, libraries, man files, etc.
/var
This directory contains variable data files such as log files, email in-boxes, web application related files, cron files, and more.