What is Linux?

Linux is an open-source, Unix-like operating system (OS) kernel that serves as the foundation for various operating system distributions (distros). It was created by Linus Torvalds in 1991 and has since become one of the most widely used OS kernels in the world.

Key Features of Linux :

1. Open Source – The source code is freely available for modification and distribution.
2. Multi-User & Multitasking – Multiple users can work on the system simultaneously, and it supports running multiple processes at the same time.
3. Security & Stability – Linux is known for its strong security features and stability.
4. Customizability – Users can modify Linux to suit their needs, with many different desktop environments (GNOME, KDE, XFCE, etc.).
5. Command-Line Power – The Linux terminal is powerful and allows users to control nearly every aspect of the system.
6. Lightweight & Efficient – Some Linux distributions (e.g., Alpine, Arch, and Debian) are designed to run on minimal hardware.

Popular Linux Distributions (Distros) :

• Ubuntu – User-friendly, great for beginners.
• Debian – Stable and reliable, often used for servers.
• Fedora – Cutting-edge software with frequent updates.
• Arch Linux – Lightweight and highly customizable.
• Kali Linux – Security-focused, used for penetration testing.
• CentOS / RHEL – Enterprise-focused, commonly used in businesses.

Where is Linux Used?

• Servers (Web servers, cloud computing, databases)
• Embedded Systems (Smart TVs, routers, IoT devices)
• Supercomputers
• Android Devices (Android is based on the Linux kernel)
• Cybersecurity & Ethical Hacking
• Programming & Development.

Linux Essential Commands :

Here are some essential Linux commands that every user should know:

* File and Directory Management

• ls – List directory contents

  ls -l   # Long format
  ls -a   # Show hidden files
  

• cd – Change directory

  cd /home/user/Documents
  

• pwd – Print working directory

  pwd
  

• mkdir – Create a new directory

  mkdir myfolder
  

• rmdir – Remove an empty directory

  rmdir myfolder
  

• rm – Remove files or directories

  rm file.txt
  rm -r myfolder  # Remove a directory and its contents
  

• cp – Copy files or directories

  cp file.txt /destination/
  cp -r dir1/ dir2/  # Copy directories
  

• mv – Move or rename files

  mv oldname.txt newname.txt
  mv file.txt /new/location/
  

* File Viewing and Editing

• cat – View file contents

  cat file.txt
  

• less – View file contents page by page

  less file.txt
  

• head – Show the first 10 lines of a file

  head file.txt
  

• tail – Show the last 10 lines of a file

  tail file.txt
  tail -f log.txt  # Continuously display new lines
  

• nano – Simple text editor

  nano file.txt
  

• vi or vim – Advanced text editor

  vi file.txt
  

* Permissions and Ownership

• chmod – Change file permissions

  chmod 755 script.sh
  chmod u+x script.sh  # Give execute permission to the user
  

• chown – Change file owner

  chown user:group file.txt
  

* Process and System Monitoring

• ps – Display running processes

  ps aux
  

• top – Show system resource usage

  top
  

• htop – Interactive process viewer (if installed)

  htop
  

• kill – Terminate a process

  kill PID
  kill -9 PID  # Force kill a process
  

• df – Show disk usage

  df -h
  

• du – Show directory size

  du -sh foldername
  

* User Management

• whoami – Show current user

  whoami
  

• who – Show logged-in users

  who
  

• id – Show user ID and group ID

  id
  

• passwd – Change user password

  passwd
  

• su – Switch user

  su username
  

• sudo – Run command as superuser

  sudo apt update
  

* Networking

• ip a – Show IP addresses

  ip a
  

• ping – Check network connectivity

  ping google.com
  

• netstat – Show network connections (deprecated, use ss)

  netstat -tulnp
  

• ss – Display network connections

  ss -tulnp
  

• wget – Download files from the internet

  wget https://example.com/file.zip
  

* Package Management

For Debian-based systems (Ubuntu, Debian):

• apt update – Update package lists

  sudo apt update
  

• apt upgrade – Upgrade all packages

  sudo apt upgrade
  

• apt install – Install a package

  sudo apt install package-name
  

• apt remove – Remove a package

  sudo apt remove package-name
  

For RHEL-based systems (CentOS, Fedora):

• yum update – Update package lists

  sudo yum update
  

• yum install – Install a package

  sudo yum install package-name
  

* Archiving and Compression

• tar – Create or extract compressed archives

  tar -cvf archive.tar foldername  # Create tar archive
  tar -xvf archive.tar  # Extract tar archive
  tar -czvf archive.tar.gz foldername  # Create gzipped tar archive
  tar -xzvf archive.tar.gz  # Extract gzipped tar archive
  

• zip – Compress files into a .zip archive

  zip -r archive.zip foldername
  

• unzip – Extract .zip files

  unzip archive.zip
  

* Searching

• find – Search for files and directories

  find /path -name "file.txt"
  

• grep – Search inside files

  grep "text" file.txt
  grep -r "text" /directory/
  

* System Information

• uname -a – Show system information
• uptime – Show system uptime
• free -h – Show memory usage
• history – Show command history
• clear – Clear terminal screen.