Overview

Open-source Unix-like OS
Popular for servers, Docker, cloud deployments, and software development
Multiple distributions: Ubuntu, CentOS, Fedora, Debian, Arch

Concepts / Theory

File System
- ext4, XFS, Btrfs; hierarchy starts from /
Users & Groups
- root = superuser, standard users, groups for permissions
Processes
- ps, top, htop, signals (kill, pkill)
Package Management
- apt (Debian/Ubuntu), yum/dnf (RedHat/Fedora)
Networking
- ifconfig/ip, netstat, firewall (ufw, iptables)
Shells
- bash (default), zsh, sh
System Services
- systemctl for managing daemons

Kernel

Command	Purpose
ls -la	List files with details
cd <dir>	Change directory
mkdir <name>	Create folder
rm <file>	Delete file
rm -rf <folder>	Delete folder recursively
chmod	Change file permissions
chown	Change owner/group
ps aux	Show all processes
top / htop	Monitor CPU/memory usage
kill <pid> / pkill <name>	Terminate process
sudo	Run command as root
apt install <package>	Debian/Ubuntu package install
yum install <package>	RedHat/Fedora package install

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Commands