🐧 Linux Basics

Linux is a free, open-source operating system kernel created by Linus Torvalds in 1991. It forms the basis of many operating systems (called "distributions" or "distros") such as Ubuntu, Debian, CentOS, and Fedora.

Linux dominates the server world — over 96% of the world's top 1 million web servers run Linux. It's known for stability, security, and flexibility.

The ls command lists files and directories in the current directory (or a specified path).

ls              # list files
ls -l           # long format (permissions, size, date)
ls -la          # include hidden files (starting with .)
ls /var/www     # list files in a specific path

Here are the essential commands every beginner should know:

pwd             # Print Working Directory (where am I?)
ls              # List files
cd /path        # Change Directory
mkdir mydir     # Create a new directory
cp file1 file2  # Copy a file
mv file1 file2  # Move or rename a file
rm file         # Delete a file (careful — no recycle bin!)
cat file.txt    # Display file contents
nano file.txt   # Edit a file (simple text editor)
sudo command    # Run a command as administrator

Use the chmod command to change file permissions. Linux permissions are split into three groups: Owner, Group, and Others. Each can have Read (r=4), Write (w=2), and Execute (x=1) permissions.

chmod 755 myfile    # rwxr-xr-x (owner: full, group/others: read+execute)
chmod 644 myfile    # rw-r--r-- (owner: read+write, others: read only)
chmod +x script.sh  # Add execute permission
chmod -w file.txt   # Remove write permission

The number 755 means: Owner=7 (4+2+1=rwx), Group=5 (4+1=r-x), Others=5 (r-x).

sudo stands for "Superuser Do". It allows a permitted user to run a command as the administrator (root) without fully logging in as root.

sudo apt update         # Update package list (needs admin rights)
sudo apt install nginx  # Install software
sudo systemctl restart apache2  # Restart a service