🐧 Linux Overview

Linux is a free, open-source, Unix-like operating system kernel that forms the core of many operating systems called "Linux distributions" (e.g., Ubuntu, CentOS, Debian). It is widely used in servers, cloud environments, mobile devices, and embedded systems.

🧱 Key Features

Open Source: Source code is freely available and modifiable.
Multiuser: Supports multiple users at once without interfering with each other.
Multitasking: Can run multiple processes simultaneously.
Security: Built-in user permissions, firewalling (iptables/nftables), and SELinux/AppArmor.
Portability: Runs on various hardware architectures, from phones to supercomputers.

🧠 Major Linux Concepts

Linux is a powerful and versatile operating system. Below are the most important concepts that form the foundation of how Linux works and is used.

🧱 1. Kernel

The Linux kernel is the core of the operating system. It handles:

Hardware abstraction
Process management
Memory management
Filesystems
Networking

🐚 2. Shell

A shell is a command-line interface (CLI) that lets users interact with the system. Common shells:

```
bash
```
```
zsh
```
```
sh
```
```
fish
```

👤 3. Users and Permissions

Linux is a multi-user system. Key concepts include:

```
root
```
: Superuser with all permissions
File ownership: user, group, others
Permissions: read (
```
r
```
), write (
```
w
```
), execute (
```
x
```
)
```
chmod
```
,
```
chown
```
,
```
usermod
```
: Tools to manage permissions and users

📁 4. Filesystem Hierarchy

Everything is a file in Linux, including devices and processes. Common directories:

```
/
```
: Root of the filesystem
```
/etc
```
: Config files
```
/home
```
: User directories
```
/var
```
: Logs and variable data
```
/usr
```
: User applications and libraries

🔧 5. Package Management

Used to install, update, and remove software.

Debian-based:
```
apt
```
,
```
dpkg
```
Red Hat-based:
```
yum
```
,
```
dnf
```
,
```
rpm
```
Arch-based:
```
pacman
```

📋 6. Processes and Services

A process is an instance of a running program.
Use
```
ps
```
,
```
top
```
,
```
htop
```
to monitor.
Services (daemons) are background tasks, often managed by
```
systemd
```
using
```
systemctl
```
.

🔐 7. Security

Security features include:

File permissions
```
sudo
```
for controlled admin access
Firewalls:
```
iptables
```
,
```
nftables
```
Security modules:
```
SELinux
```
,
```
AppArmor
```

🌐 8. Networking

Linux offers powerful networking tools:

```
ip
```
,
```
ifconfig
```
: Interface management
```
ping
```
,
```
netstat
```
,
```
ss
```
,
```
traceroute
```
: Diagnostics
Network services: SSH (
```
sshd
```
), HTTP (
```
nginx
```
,
```
apache
```
)

📜 9. Scripting

Shell scripting automates tasks:

Bash scripts (
```
.sh
```
files)
Conditional logic, loops, variables
Used for deployments, cron jobs, system automation

📦 10. Virtualization and Containers

Virtualization: Run multiple OSes via tools like KVM, VirtualBox
Containers: Lightweight, isolated environments (e.g., Docker)

Dockerfile