Linux Overview Lecture Notes

What is Linux?

• Linux is the kernel that powers the Linux operating system.
• The kernel manages hardware and resources, and separates processes into kernel and user land for security.

Linux Distributions

• Different types of operating systems based on the Linux kernel include GNU/Linux and Android.
• A Linux distribution is a combination of the Linux kernel and other software.
• Examples of families of distributions:
  • Red Hat Family (e.g., Fedora, CentOS)
  • Debian Family (e.g., Debian, Ubuntu, Mint)
  • Source Code Distributions (e.g., Arch, Gentoo)

Red Hat Package Management

• RPM files are used for package management in Red Hat family.
• RPM files track installed packages and their dependencies.

Debian Package Management

• Debian uses .deb files for package management.
• Focuses more on user experience compared to Red Hat.

Kernel Initialization and Systemd

• The kernel initializes processes with init, which has evolved to systemd for better organization.
• Systemd starts services in parallel, improving boot time efficiency.

Installation Considerations

• Ensure machine can boot installation media (CD, USB, network).
• Hardware requirements include hard drive space and RAM.
• Video card and wireless card compatibility are important.

Installation Methods

• Installation can be done via DVD, USB, or network.
• Set correct time and date during installation.

Software Selection

• Choose software packages during installation;
  • Minimal install for servers.
  • Full install for desktop environments.

Partitioning

• Linux partitions include root, swap, and boot partitions.
• LVM (Logical Volume Management) allows flexible volume resizing.

File System

• File systems must be formatted for use.
• Common file systems: ext4, xfs, btrfs.

User Management

• Root user has total control; create additional users for security.
• Use strong passwords and unique usernames.

Boot Process

• The bootloader loads the kernel, followed by init/systemd.
• Kernel processes manage system resources and user processes.

Command-Line Navigation

• Basic commands: pwd, ls, cd, cat, etc.
• Environment variables can be set using the export command.

File Management

• Create, edit, move, and delete files using commands like touch, mv, rm, nano, etc.

Networking

• Configure hostname, network settings (DHCP/static), and firewall rules.

System Logs

• Log files are stored in /var/log/.
• Logs include messages, secure logs, mail logs, and more.

Troubleshooting

• Check system logs for errors, verify services are running, and monitor network settings.

Kernel Modules

• Kernel modules are used to add functionality to the Linux kernel, such as device drivers.
• Use lsmod to see loaded modules, modprobe to load/unload them.

DHCP Overview

• DHCP automates the IP address assignment process using messages and leases.
• Security concerns include rogue DHCP servers and spoofed addresses.

DNS Overview

• DNS translates domain names to IP addresses, reducing reliance on static host files.
• Security issues include spoofing and DNS redirection.

SNMP Overview

• SNMP gathers statistical information from network devices.
• Uses UDP for communication; security concerns include weak community strings.

Apache Web Server

• Apache serves web pages over HTTP/HTTPS.
• Configuration files are typically found in /etc/httpd/.

MySQL/MariaDB Overview

• MariaDB is a drop-in replacement for MySQL with a focus on open-source.
• SQL commands include SELECT, INSERT, UPDATE, DELETE.

Summary

• Linux is a powerful operating system used widely in servers and desktops.
• Understanding the kernel, distributions, package management, and system administration is crucial for effective use.