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Linux Fundamentals

A brief overview of the fundamentals of Linux.

Author: Kirstie Martinka (Kasten) | Published: 2025-2-16

Linux Fundamentals

We will be covering the following topics:

  1. Linux File System
  2. Changing Directories
  3. Display Contents of a Directory
  4. Creating and Editing Files Using Vi
  5. Modifying Files
  6. Creating Folders
  7. User and Permission Management
  8. Networking Basics in Linux
  9. Package Management and Software Installation

Linux File System

There are THREE different “root” terms in Linux.

  1. The root user – This is the administrator account.
  2. The root filesystem – This is the / of the filesystem hierarchy. Think of this as C:> in Windows.
  3. The root home folder – This is the home folder of the root user, located in the root of the filesystem. It is located at /root.

Logging in as root > logging in as the admin account

Going into the root of the system > /

Going into the root home folder, or ~ as root > /root.

This structure helps users and applications access files systematically. Common directories include:

  • /bin (binary executables)
  • /etc (configuration files)
  • /home (user home directories)
  • /var (variable data like logs)

Another representation of the Linux file system:

/ 
├── bin     - Essential binaries (e.g., ls, cp) 
├── boot    - Bootloader files (e.g., kernel, initramfs) 
├── dev     - Device files (e.g., /dev/sda) 
├── etc     - System configuration files 
├── home    - User home directories 
│   ├── user1 
│   └── user2 
├── lib     - Shared libraries for essential binaries 
├── media   - Mount points for removable media 
│   ├── usb 
│   └── dvd 
├── mnt     - Temporary mount points 
├── opt     - Optional software packages 
├── proc    - Kernel and process information (virtual filesystem) 
├── root    - Home directory for the root user 
├── run     - Runtime data for processes 
├── sbin    - System binaries (e.g., reboot, fdisk) 
├── srv     - Data for services (e.g., web server files) 
├── sys     - Kernel and hardware information (virtual filesystem) 
├── tmp     - Temporary files (cleared on reboot) 
├── usr     - User programs and data 
│   ├── bin   - User binaries 
│   ├── lib   - Shared libraries for user binaries 
│   ├── share - Shared resources (e.g., man pages) 
│   └── local - Locally installed software 
└── var     - Variable files (e.g., logs, cache, spool) 
    ├── log   - Log files 
    ├── cache - Application caches 
    └── spool - Queued tasks (e.g., mail, printing)

Changing Directories

Using the file system from above, if you were in /var/log and wanted to navigate to /home/user1:

  1. cd /home/user1
    • This is an absolute path.
  2. cd ../../home/user1
    • This is a relative path.
  3. cd .. > cd .. > cd home > cd user1

Others include:

  1. cd ~
    • This will take you to your home directory.
    • /home/username if USER, /root if ROOT
  2. cd ~username
    • This will take you to the home directory of the user specified.

Display Contents of a Directory

  1. ls
    • This will show the contents of the directory you are in.
  2. ls -la
    • This will show more information about the files, like ownership, permissions, hidden files, and size.
    • -l shows detailed information, -a shows all files (including hidden files)
  3. tree
    • This shows a more graphical view of the files and folders.
    • To install, run the command:
      • sudo dnf -y install tree

Creating and Editing Files Using Vi

Navigate to the directory the file is to be created in.

  1. touch filename.txt
    • This will create a blank file.
    • Can also open Vi and create a new file at the same time: vi newfile.txt
  2. vi filename.txt
  3. Hit the "i" key to enter INSERT mode.
    • Edit the file as necessary.
    • Hit the "esc" key to escape.
  4. To save and quit:
    • :wq to write the file to disk (saves), and quits
    • :q! to force Vi to quit without saving

Modifying Files

  1. mv originalFile.txt renamedFile.txt
    • This will rename a file.
  2. cp firstFolder/file secondFolder/file
  • This will copy a file from one folder to another.
  • Using a WildCard Character:
    • cp firstFolder/file secondFolder/file
    • For example, (*.txt) matches all files with a .txt extension, and (file *) matches any file starting with file.
  1. rm file
    • This will remove/delete a file.

Creating Folders

  1. mkdir newFolder
  2. mkdir newFolder/subFolder
    • Creates a folder within a folder
  3. mkdir -p newFolder/subFolder
    • Creates both folders at once

To remove a folder:

  • rm -d folder

A folder must be empty prior to removing the folder. To remove files inside of the folder:

  • rm folder/*

BRUTE FORCE DELETION:

  • rm -rf folder
    • -r for recursive - go through all the files and folders under this folder and wipe it all out
    • -f for force - do not prompt for verification
  • DO NOT RUN THIS COMMAND: sudo rm -rf /
    • This will delete every file, folder, and device from your Linux machine. This rm command deletes everything starting in the root file system.

User and Permission Management

Add a user:

  • sudo adduser username

Specify a name to the user:

  • *sudo useradd username -c "Person Name"

Verify user:

  • cat /etc/passwd
    • This lists the account, name, UID, GUI, and shell for each user

Specify the password for user:

  • sudo passwd username

Create a group:

  • sudo groupadd groupName

Add user to a group:

  • sudo usermod username -aG groupName

The commands chmod, change mode, and chown, change owner, are used to change permissions on a file or folder:

read, write, execute flags

Networking Basics in Linux

Use ipconfig or ip addr to display the system's network configuration.

Test network connectivity to a website, like google.com, using the ping command.

Download files using the command line:

  • curl URL
    • Client URL
    • Used to send and receive data
    • Supports different protocols like HTTP, HTTPS, and FTP
  • wget URL
    • Web Get
    • Used only for downloading files
    • Supports different protocols like HTTP, HTTPS, and FTP

Package Management and Software Installation

  1. sudo dnf update
    • This updates the list of packages (software) available to install or update.
  2. sudo dnf upgrade
    • This will upgrade any out of date packages on your system to the latest version.

Installing software:

  • sudo apt install software OR sudo dnf install software
    • This installs the software on your system.
  • sudo systemctl enable software
    • This enables the software.
  • sudo systemctl start software
    • This starts the software.
  • sudo systemctl status software
    • This can help verify that the service has started and is running.
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