What is Linux?
 Linux in short
Note: The text in bold are keywords. Please remember them.
Linux is a complex operating system based on UNIX system V but we can't call it UNIX because it is open source.
The word UNIX is reserved and if someone wants to use it he must pay.
Open source software are not commercial. That is, the source code and the documentation are available to the public at no cost.
The defining component of Linux is the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds.
We will discuss more about the Linux kernel later.
Linux is very robust and secure. The main advantages of Linux are:
- Multi-user: Multi-user software is software that allows access by multiple users of a computer.
- Multitasking: Multitasking is a concept of performing multiple tasks (also known as processes) over a certain period of time by executing them concurrently.
- Modular: You can add or remove modules in the kernel when the system is operational. Modules = drivers in Windows.
- Secure: No viruses in Linux!
- Network based: Client <---> server model, TCP/IP.
- Portable: Available for all kind of architecture: x86 architecture, Power Architecture, SPARC. For a complete list visit https://en.wikipedia.org/wiki/List_of_Linux-supported_computer_architectures
- Scalable: Scalability is the capability of a system, network, or process to handle a growing amount of work, or its potential to be enlarged in order to accommodate that growth.
There are two types of Linux installations out there: Server and Desktop.
Linux is very popular as server installation but not as desktop.
Every aspect of Internet is based on server-client model. This means that a client sends a request to the server and the server handles the request and sends back the answer to the client. That's it, servers handles services.
A client could be any kind of system, a PC, laptop, mobile phone or a car.
 Linux distribution
There are many Linux distributions. The most popular are Red Hat, commercial and Ubuntu, non commercial.
For a complete list visit: https://en.wikipedia.org/wiki/List_of_Linux_distributions
In this tutorial we will use Ubuntu server which is non-graphical. You use only CLI, Command Line Interpreter, which is built-in the shell.
The shell provides a traditional Unix-like command line user interface. Users direct the operation of the computer by entering commands as text for a command line interpreter to execute, or by creating text scripts of one or more such commands. Users typically interact with a Unix shell using a SSH.
 Links and documents
There are tons of documents and tutorial out there.