Linux Fundamentals (What to Learn First)

Linux is everywhere! From web servers to smartphones, understanding its fundamentals unlocks a deeper appreciation for the technology we use every day.

This post will help you to understanding the core concepts of Linux, making you a savvy user in no time. (But make sure to practice these to become expert)

System Fundamentals

• Kernel - The core of the operating system
• Shell - A program that provides a command line interface to the operating system 
• System calls - Functions that provide an interface for user programs to access the operating system's functionalities
• System libraries - Collections of functions and routines used by programs
• Processes - An instance of a computer program that is being executed
• User - An account on a computer system that is used to identify a person or process
• Group - A collection of users that share common permissions on a computer system
• Permissions - Controls who can access a file or directory and what they can do with it
• Ownership - Refers to the user and group that owns a file or directory

Filesystem Hierarchy

• /etc: The directory on a Linux system that stores configuration files.
• /var: The directory on a Linux system that stores variable data files.
• /home: The directory on a Linux system that stores user data files.
• /root: The home directory of the root user on a Linux system.
• /bin: The directory on a Linux system that stores essential executable programs.
• /sbin: The directory on a Linux system that stores executable programs for system administration.
• /usr/bin: The directory on a Linux system that stores user executable programs.
• /usr/sbin: The directory on a Linux system that stores system administration executable programs.

• /tmp: The directory on a Linux system that stores temporary files.

User Management

• useradd: A command in Linux used to create a new user account.

• usermod: A command in Linux used to modify an existing user account.

• /etc/passwd: A file on a Linux system that stores information about user accounts.

• /etc/shadow: A file on a Linux system that stores hashed passwords for user accounts.

• UID (User ID): A unique identifier for a user account on a Linux system.

• GID (Group ID): A unique identifier for a group of users on a Linux system.

Package Management

• apt: A package manager for Debian-based Linux systems.

• yum: A package manager for Red Hat-based Linux systems.

• dnf: A newer package manager that replaces yum in Red Hat-based Linux systems.

• DEB (Debian package file): A type of package file used by Debian-based Linux systems.

• RPM (Red Hat Package Manager): A type of package file used by Red Hat-based Linux systems.

• Tarball: A compressed archive file format used to distribute software in Linux.

Security

• Firewall: A software program that filters incoming and outgoing network traffic.

• iptables: A command-line tool for managing firewall rules in Linux.

• firewalld: A firewall management tool for Linux that is easier to use than iptables.

• SELinux (Security-Enhanced Linux): A security system for Linux that restricts what programs can do.

Processes

• PID (Process ID): A unique identifier for a running process on a Linux system.

• ps: A command in Linux used to display information about running processes.

• Foreground process: A process that is currently running and has the user's attention.

• Background process: A process that is running in the background and does not have the user's attention.

Command-line Tools

• Shell: A program that provides a command-line interface for interacting with the Linux operating system.

• grep: A command-line tool used to search for text in files.

• sed: A command-line tool used to edit text files.

• awk: A command-line tool used to process text files.

• kill: A command-line tool used to send a signal to a process.

• top: A command-line tool used to display information about running processes.

• man: A command-line tool used to display the manual page for a command.

Text Editors

• nano: A simple text editor for Linux.

• qedit: A more advanced text editor for Linux.

Networking

• TCP/IP (Transmission Control Protocol/Internet Protocol): The suite of protocols used for communication over the internet.
• ifconfig: A command-line tool used to configure network interfaces.
• netstat: A command-line tool used to display information about network connections.
• scp: A command-line tool used to securely copy files between computers.
• ssh: A command-line tool used to securely login to a remote computer.
• wget: A command-line tool used to download files from the internet.