Linux Installation, Boot Process, Package Mgmt & CLI Admin

Key Concepts and Installation Methods

1. Linux Installation Methods

Linux can be installed in multiple ways, each suited for different scenarios:

Text-Based vs. Graphical Installation

• Text-based: Faster, less resource-intensive, preferred for servers or remote installations.
• Graphical: User-friendly, ideal for beginners or desktop systems.

Installation Media

• USB/DVD: Most common method.
• Network (PXE): Used in large-scale deployments (e.g., corporate environments).
• Cloud (AWS, Azure, GCP): For virtualized or cloud-based Linux instances.

Partitioning Schemes

Linux supports various partitioning schemes, including:

• MBR (Master Boot Record): Legacy, supports up to 4 primary partitions.
• GPT (GUID Partition Table): Modern, supports up to 128 partitions, required for systems >2.2TB.

The Linux Boot Process

The boot process is a critical sequence that loads the operating system into memory. Here’s a step-by-step breakdown:

1. BIOS/UEFI Initialization

• The system’s firmware (BIOS/UEFI) performs a Power-On Self-Test (POST) to check hardware.
• Detects bootable devices (e.g., USB, HDD, network).

2. Bootloader (GRUB)

• GRUB (GRand Unified Bootloader) is the default bootloader in most Linux distributions.
• Allows selection of the OS/kernel to boot (useful for dual-boot systems).
• Loads the kernel and initramfs (initial RAM filesystem).

sequenceDiagram
    participant BIOS
    participant GRUB
    participant Kernel
    participant Initramfs
    participant RootFS

    BIOS->>GRUB: Load bootloader
    GRUB->>Kernel: Load kernel + initramfs
    Kernel->>Initramfs: Mount root filesystem
    Initramfs->>RootFS: Hand over control
    RootFS->>Systemd: Start services

3. Kernel Initialization

• The kernel initializes hardware (CPU, memory, storage).
• Loads drivers and mounts the root filesystem.

4. Init System (systemd)

• systemd is the default init system in modern Linux distributions.
• Manages services, processes, and system states (runlevels).

Runlevels (SysVinit) vs. Targets (systemd)

Package Management in Linux

Linux distributions use different package management systems:

1. RPM (Red Hat Package Manager)

• Used by RHEL, CentOS, Fedora.
• Commands:

  rpm -ivh package.rpm    # Install
  rpm -e package          # Erase (remove)
  rpm -qa                # Query all installed packages
  

2. DEB (Debian Package)

• Used by Debian, Ubuntu.
• Commands:

  dpkg -i package.deb     # Install
  dpkg -r package         # Remove
  dpkg -l                # List packages
  

3. Advanced Package Managers

• yum/dnf (RHEL/Fedora): Handles dependencies automatically.

  dnf install package     # Install (Fedora/RHEL 8+)
  yum install package     # Install (older RHEL/CentOS)
  

• apt (Debian/Ubuntu): Uses .deb packages.

  apt update              # Update package list
  apt install package     # Install
  

Comparison Table

Command-Line Administration

1. File Operations

2. File Permissions

Linux uses rwx (read, write, execute) permissions for users, groups, and others.

chmod 755 file.txt   # Owner: rwx, Group/Others: r-x
chown user:group file.txt  # Change owner/group

Permission Table

3. Process Management

Process States

stateDiagram-v2
    [*] --> Running
    Running --> Sleeping
    Running --> Stopped
    Running --> Zombie
    Sleeping --> Running
    Stopped --> Running
    Zombie --> [*]

In the Real World

1. eSewa (Nepal)

   • Uses Linux servers for backend services (e.g., payment processing, user authentication).
   • Package management (yum/dnf or apt) ensures software updates are secure and consistent.
   • GRUB bootloader is used in their data center servers for reliable booting.

2. Ncell (Nepal)

   • Linux-based routers manage network traffic for millions of subscribers.
   • Firewall rules (iptables/nftables) are configured via CLI to filter malicious traffic.
   • Systemd ensures critical services (like billing systems) restart automatically after crashes.

3. Daraz (Global)

   • Ubuntu servers handle order processing, inventory management, and user logins.
   • Cron jobs automate tasks like sending order confirmations or updating product listings.
   • SELinux/AppArmor enforces security policies to prevent unauthorized access.

Worked Example: Configuring a Minimal Linux Server

Scenario: You need to set up a web server on a CentOS 7 machine with:

• Only essential services running.
• Automatic security updates.
• Basic firewall rules.

Step 1: Install Minimal Linux

• Boot from CentOS 7 ISO (USB/DVD).
• Choose "Server with GUI" (if needed) or "Minimal Install".
• Partition using LVM (Logical Volume Manager) for flexibility.

Step 2: Configure Bootloader (GRUB)

• Edit /etc/default/grub to set default boot options:

  GRUB_TIMEOUT=5
  GRUB_DEFAULT=0
  

• Update GRUB:

  grub2-mkconfig -o /boot/grub2/grub.cfg
  

Step 3: Install Essential Packages

• Update package lists:

  yum update -y
  

• Install Apache (httpd) and firewalld:

  yum install httpd firewalld -y
  

Step 4: Configure Firewall

• Allow HTTP/HTTPS traffic:

  firewall-cmd --permanent --add-service=http
  firewall-cmd --permanent --add-service=https
  firewall-cmd --reload
  

Step 5: Enable Automatic Updates

• Install yum-cron for automatic updates:

  yum install yum-cron -y
  systemctl enable yum-cron
  systemctl start yum-cron
  

Step 6: Start Services

• Enable and start httpd and firewalld:

  systemctl enable httpd
  systemctl start httpd
  systemctl enable firewalld
  systemctl start firewalld
  

Result: A secure, minimal Linux web server ready for deployment.

Exam Tip

1. Understand the Boot Process: Be able to explain BIOS → GRUB → Kernel → systemd in detail. Expect questions on GRUB configuration or runlevels/targets.
2. Package Management: Know the difference between RPM (yum/dnf) and DEB (apt). Practice installing/removing packages in a lab.
3. File Permissions: Memorize chmod numbers (e.g., 755, 644) and chown syntax. Common exam questions test setting permissions for web directories.
4. Process Management: Know how to list (ps), kill (kill), and monitor (top) processes. Expect a question on process states (Running, Sleeping, Zombie).
5. Real-World Scenarios: Relate concepts to eSewa (payment systems), Ncell (networking), or Daraz (web servers). For example:
   • "How would you secure a Linux server hosting an eSewa payment gateway?" → Firewall rules, SELinux, automatic updates.
   • "What bootloader does Ncell use in its routers?" → GRUB or custom firmware.