1.9 - Linux

Overview of Linux Operating System

• Linux is a free operating system similar in style and operation to older Unix systems.

• There are many types of Linux, known as Linux distributions, including:

  • Ubuntu

  • Debian

  • Red Hat

Advantages of Linux

• No cost to install and use the operating system.

• Flexibility to run on various hardware platforms:

  • Compatible with both new and older computers.

• Support from a passionate and active user community.

• Updates and device drivers are primarily managed by users rather than a centralized company.

Installation and Boot Process

• When a computer is powered on, the Basic Input/Output System (BIOS) initiates the boot process.

  • BIOS is configured to list all storage devices connected to the system.

  • One storage device is designated as the bootable device.

  • The BIOS transfers the boot process to the boot device.

• The boot device runs a bootloader located in the boot sector, responsible for starting the installed operating system.

BIOS Configuration

• Users can configure the BIOS startup sequence to define boot order.

  • Options may include:

  • USB drives

  • Optical drives

  • Solid State Drives (SSDs)

  • Hard drives

• Modern BIOS is often a Unified Extensible Firmware Interface (UEFI).

  • UEFI contains details on starting the operating system from a specified storage drive.

  • It uses an EFI System Partition (ESP) to list associated operating system EFI files.

EFI System Partition (ESP)

• Contains EFI files needed to launch different operating system kernels:

  • Example: load-a EFI file starts one OS kernel, load-b EFI starts another.

• Users select the desired operating system on the screen, initiating the respective OS kernel.

Kernel and Its Functions

• The kernel is the core component of the operating system, handling:

  • System start

  • Loading device drivers

  • Managing executing applications

  • Interfacing with the user.

• The kernel operates from a designated memory area known as kernel space, distinct from user space where user applications run.

• Kernel updates may occur for:

  • New features

  • Bug fixes

  • Security patches

System Management with Systemd

• Systemd manages background processes in Linux, analogous to services in Windows.

  • Background processes are referred to as daemons.

• Systemd is initiated by the kernel upon system boot and is responsible for starting and managing required services.

• It provides a standardized toolset for system startup and daemon management.

User Management in Linux

• The root user in Linux has full control over the operating system, similar to the administrator in Windows.

• Administrative tasks (e.g., modifying system files) require root permissions.

Command-Line Interface vs. GUI

• Linux can be operated fully via command line, with the graphical user interface (GUI) as an optional feature.

• Most system configuration is conducted through text-based configuration files.

User Management File: /etc/passwd

• User information is stored in /etc/passwd, which lists:

  • Username

  • Password placeholder (typically an ‘x’)

  • User ID

  • Group ID

  • Home directory

  • Shell command

• Password security includes moving actual passwords to a separate file:

  • Shadow file located in /etc/ contains hashed passwords and is secured against unauthorized access.

Important Files in Linux

• hosts file (/etc/hosts)

  • Associates Fully Qualified Domain Names (FQDNs) with IP addresses.

  • Example entry: 10.1.10.224 staging.professormesser.com

  • Precedes DNS for local name resolution; can override DNS settings.

• resolv.conf (/etc/resolv.conf)

  • Contains a list of DNS servers for name resolution.

  • Lists are checked by the OS for DNS settings for network operations.

• fstab (/etc/fstab)

  • Details the file system table for mounting storage devices.

  • Ensures all drives connected to the system are properly mounted during startup.