Ubuntu

Table of Content

🎯 Objectives

🎯 Objectives

Master the core concepts of the Linux terminal and shell.
Understand the Linux File Hierarchy Standard (FHS) and how to navigate it.
Learn how to manage system variables and environment settings.
Build skills for managing software packages with APT.

📸 Snapshot: The “Save Game” of VMs

A snapshot is a recorded state of a virtual machine at a specific point in time. It includes the state of the disk, RAM, and configuration.

How to use it:
1. Take a Snapshot: Before a risky task (like editing a core config file), save the current state.
2. Restore/Revert: If the system breaks, roll back to the saved “healthy” state.
3. Delete: After confirming the changes are stable, delete the snapshot to save disk space.

🖥️ Terminal vs. Shell vs. Command

Terminal: The graphical window or interface that provides a text-based environment (e.g., GNOME Terminal, iTerm2).
Shell: The interpreter (e.g., Bash, Zsh). It takes your input, translates it for the kernel, and returns the result.
Command: The specific instruction or program you tell the shell to run (e.g., ls, cd).

🐚 Different Types of Shells

sh (Bourne Shell): The original Unix shell. It is simple, but it lacks modern features.
bash (Bourne Again Shell): The standard shell for many Linux distros (including Ubuntu).
zsh (Z Shell): Highly customizable and popular for its “Oh My Zsh” plugin framework.
fish (Friendly Interactive Shell): Known for excellent auto-suggestions and a user-friendly experience out of the box.

🛠️ Structure of a Command

A typical command follows this pattern: ls -al /etc

Command (ls): The program to execute.
Options/Flags (al): Modifies how the command behaves (e.g., show all files in a long list).
Arguments (/etc): The target the command acts on.

📚 Getting Help: Documentation Tools

-help: A quick summary of options built into the command.
man (Manual): The official, detailed manual for a command.
tldr: A community-driven tool that provides practical examples of common use cases.

🆘 How to Help Yourself When Stuck

Read the Error Message: Many Linux errors tell you exactly what is wrong (e.g., “Permission denied”).
Use Tab Completion: Avoid typos by letting the shell complete file and command names.
History: Use the up arrow to find previous successful commands.
The Internet is Your Friend: Search the error message on StackOverflow or in official documentation.

pwd: Print Working Directory (Where am I?).
ls: List files in the current folder.
cd: Change Directory to move between folders.
mkdir: Create a new directory.
touch: Create a new empty file.
cp: Copy files or directories.
mv: Move or rename files/directories.
rm: Remove (delete) files or directories.

📂 Linux File Hierarchy Standard (FHS)

FHS Minimap

/: The root. Everything starts here.
/bin & /usr/bin: Basic user commands.
/etc: System-wide configuration files.
/home: Personal folders for users.
/root: The home folder for the superuser.
/var: Variable data, such as logs and databases.

Absolute Path vs. Relative Path

Absolute Path: Always starts from the root (/). (e.g., /home/ubuntu/docs/test.txt).
Relative Path: Starts from your current location (e.g., docs/test.txt or ../test.txt).

The Versatility of `cd`

cd ~: Go to your home directory.
cd ..: Move up one level.
cd -: Return to the previous directory.
cd /: Go to the very start (root).

Windows vs. Linux FHS

Feature	Windows	Linux
Drive Logic	C:, D:, E: (Physical partitions)	Single Tree (Root `/`)
Path Separator	Backslash (`\\`)	Forward slash (`/`)
Case Sensitivity	Mostly Case-Insensitive	Strictly Case-Sensitive

The FHS Metaphor

Think of the Linux FHS like a large library:

The root (/) is the building itself.
/etc is the administrative office (rules and settings).
/bin is the tool shed (items everyone uses).
/home is the private study rooms (individual spaces).

Mapping: Windows vs. Linux

C:\\Users ↔ /home
C:\\Windows ↔ /usr or /boot
C:\\Program Files ↔ /usr/bin or /opt
Control Panel ↔ /etc

⚙️ Configuration & Variables

Main Files in `/etc`

/etc/passwd: User account information.
/etc/shadow: Secure encrypted passwords.
/etc/hostname: The computer name.
/etc/hosts: Local IP-to-hostname mapping.

6 Main Directories Comparison

Directory	Full Name	Purpose
`/bin`	Binaries	Essential command binaries for all users.
`/etc`	Etcetera	System-wide configuration files.
`/home`	Home	User home directories (personal data).
`/root`	Root	Home directory for the root user.
`/tmp`	Temporary	Temporary files (often cleared on reboot).
`/usr`	User System Resources	Secondary hierarchy for user read-only data.

🔍 Exploration Toolkit (4 Tools)

find: Search for files by name, size, or time.
grep: Search for specific text patterns inside files.
which: Show the full path of the command you are running.
locate: Quickly find files using a pre-built database.

🧬 Variables & Shell Customization

Environment Variables

These variables define system behavior and are available to child processes. Examples include USER, HOME, and PATH.

Environment vs. Local vs. Alias

Environment Variable: Global. Available to the whole session and apps (e.g., export VAR=1).
Local Variable: Exists only within the current shell instance.
Alias: A custom shortcut for a longer command (e.g., alias ll='ls -al').

The `$PATH` Logic

When you type a command (like python), the shell searches the directories listed in $PATH from left to right. It runs the first match it finds. If nothing is found, you get “Command not found.”

Persistence: Temporary vs. Permanent

Temporary: Typing export VAR=val in the terminal lasts only until you close that window.
Permanent: Add the command to a configuration file so it loads every time you log in.

Configuration Files

.bashrc: Personal settings for non-login shells (your daily terminal).
.profile: Personal settings for login shells.
/etc/profile: System-wide settings for all users.

📦 Package Management (APT)

8 Essential APT Commands

sudo apt update: Refresh the list of available software.
sudo apt upgrade: Install the latest versions of currently installed packages.
sudo apt install: Download and install a new program.
sudo apt remove: Uninstall a program.
sudo apt purge: Uninstall a program and delete its config files.
sudo apt autoremove: Remove unused dependencies.
apt search: Look for a program in the online repository.
apt show: View detailed info about a specific package.

Update vs. Upgrade (Common Misunderstanding)

update: Updates the list of what is available. It does not install anything.
upgrade: Downloads and installs newer versions based on the updated list.

Search & Show

apt search nginx: “Is there a package called nginx?”
apt show nginx: “What version is it, how big is it, and what does it do?”

Install vs. Remove vs. Purge

Install: Adds the program.
Remove: Removes the program, but keeps any custom settings and config files.
Purge: Removes the program and deletes its configuration files.

3 Main Package Tools Comparison

Tool	Level	Description
dpkg	Low-level	Installs individual `.deb` files. It does not handle dependencies.
APT	High-level	The modern standard. It handles dependencies automatically via the internet.
Snap/Flatpak	Containerized	Universal packages that include their own libraries (larger, but works everywhere).

🛡️ APT Safety Checklist

Always sudo: Package management requires administrator privileges.
Update first: Always run apt update before installing something new.
Read the prompt: Check what apt is about to delete or install before pressing ‘Y’.

[ ] Avoid mixing: Try to use only one package manager (like APT) to avoid library conflicts.	Debian / Ubuntu	Ubuntu, Mint	Pros: User-friendly, huge community. Cons: Can be bloated. Usage: Beginners, Web Servers.
	Red Hat (RHEL)	RHEL, Rocky, Alma	Pros: Enterprise stability, long support. Cons: Paid support (RHEL). Usage: Corporate environments.
	Arch Linux	Arch, Manjaro	Pros: Always latest software (Rolling). Cons: High difficulty. Usage: Power users, enthusiasts.

4. Virtualization & Infrastructure

🏗️ VM vs. Container

Virtual Machine (VM):
- Virtualizes Hardware.
- Includes a full Guest OS for every instance.
- Heavy resource usage, slow boot, but high isolation.
Container (Docker):
- Virtualizes the Operating System.
- Shares the Host Kernel.
- Lightweight, starts in seconds, “write once, run anywhere” efficiency.

🌐 Client-Server Structure

Server: A machine or process that “listens” for requests and provides a service (Web, DB).
Client: An application (like a Browser or SSH terminal) that requests a service from the server.

5. Remote Environment Setup

🚪 Port Forwarding

Concept: Connecting a port on your physical computer (Host) to a port on your virtual machine (Guest).
Setup: Map Host Port 2222 → Guest Port 22 in VirtualBox settings. This allows you to SSH into the VM from your main desktop.

🔑 SSH Remote Connection Guide

SSH (Secure Shell) is the industry standard for secure remote management.

Verify Service: systemctl status ssh
Standard Connection: ssh username@server_ip

Connection via Port Forwarding:

 ssh -p 2222 username@127.0.0.1
 ### OR
 ssh -p 2222 username@localhost