Beginner's Guide to Linux Basics

Linux Fundamentals

1. Introduction to Linux

• What is Linux?

  • Linux is a Unix-like, open-source operating system kernel created by Linus Torvalds in 1991.

  • It is widely used in various computing environments, from servers and desktops to embedded systems and supercomputers.

2. Linux Distributions

• Common Distributions:

  • Ubuntu: User-friendly, widely used for desktops and servers.

  • CentOS/RHEL: Enterprise-focused, stable and secure.

  • Debian: Known for stability and robustness.

  • Fedora: Cutting-edge features, community-driven.

  • Arch Linux: Rolling release model, highly customizable.

3. Linux File System Hierarchy

• Structure:

  • / (Root): The top-level directory.

  • /bin: Essential command binaries.

  • /boot: Boot loader files.

  • /dev: Device files.

  • /etc: Configuration files.

  • /home: User home directories.

  • /lib: Shared libraries.

  • /media: Mount points for removable media.

  • /mnt: Temporary mount points.

  • /opt: Optional software packages.

  • /proc: Kernel and process files.

  • /root: Root user's home directory.

  • /sbin: System binaries.

  • /tmp: Temporary files.

  • /usr: User utilities and applications.

  • /var: Variable data files.

4. Basic Commands

• File and Directory Operations:

  • ls: List directory contents.

  • cd: Change directory.

  • pwd: Print working directory.

  • mkdir: Create directories.

  • rmdir: Remove empty directories.

  • rm: Remove files or directories.

  • cp: Copy files or directories.

  • mv: Move or rename files or directories.

• File Viewing and Editing:

  • cat: Concatenate and display file contents.

  • less: View file contents page by page.

  • more: View file contents page by page.

  • nano: Simple text editor.

  • vi/vim: Advanced text editor.

• File Permissions and Ownership:

  • chmod: Change file modes or Access Control Lists.

  • chown: Change file owner and group.

  • chgrp: Change group ownership.

• Process Management:

  • ps: Report a snapshot of current processes.

  • top: Display Linux tasks.

  • kill: Send a signal to a process.

  • killall: Kill processes by name.

  • bg: Resume a suspended job in the background.

  • fg: Bring a background job to the foreground.

5. Package Management

• Debian-based Systems (e.g., Ubuntu):

  • apt-get: Package handling utility.

  • dpkg: Debian package manager.

• Red Hat-based Systems (e.g., CentOS, RHEL):

  • yum: Package manager for RPM-based distributions.

  • rpm: RPM package manager.

6. User and Group Management

• User Commands:

  • useradd: Add a new user.

  • usermod: Modify a user account.

  • userdel: Delete a user account.

  • passwd: Change user password.

• Group Commands:

  • groupadd: Add a new group.

  • groupmod: Modify a group.

  • groupdel: Delete a group.

7. Networking Basics

• Commands:

  • ifconfig: Configure network interfaces.

  • ip: Show/manipulate routing, devices, policy routing, and tunnels.

  • ping: Send ICMP ECHO_REQUEST to network hosts.

  • netstat: Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships.

  • ssh: OpenSSH SSH client (remote login program).

8. Shell Scripting

• Basics:

  • Writing scripts using shell languages like Bash.

  • Using variables, loops, and conditionals.

• Example Script:

    #!/bin/bash
    echo "Hello Kpranit!"
    for i in {1..5}
    do
      echo "Welcome $i times"
    done
  

9. System Monitoring and Performance

• Commands:

  • top: Task manager.

  • htop: Interactive process viewer.

  • vmstat: Report virtual memory statistics.

  • iostat: Report CPU and I/O statistics.

  • free: Display amount of free and used memory in the system.

  • df: Report file system disk space usage.

  • du: Estimate file space usage.

10. Security

• Firewall Configuration:

  • iptables: Administration tool for IPv4 packet filtering and NAT.

  • ufw: Uncomplicated Firewall (frontend for iptables).

• SSH Configuration:

  • Secure remote login and file transfer.

  • Use of public and private keys for authentication.

• File Permissions:

  • Understanding and setting read, write, and execute permissions.

  • Using chmod, chown, and chgrp.

Conclusion

Linux fundamentals cover a wide range of topics, from understanding the file system hierarchy and basic command-line operations to more advanced topics like shell scripting and system security. Mastery of these fundamentals provides a solid foundation for using Linux effectively in various environments, whether for personal use, development, or managing servers in a professional setting.