Raspberry Pi Operating System

Raspbian

No matter how good the hardware of the Raspberry Pi is, without an operating system it is just a piece of silicon, PCB, and a few other materials. There are several different operating systems for the Raspberry Pi, including RISC OS, Pidora, Arch Linux, and Raspbian. Currently, Raspbian is the most popular Linux-based operating system for the Raspberry Pi. Raspbian is an open source operating system based on Debian, which has been modified specifically for the Raspberry Pi (thus the name Raspbian). Raspbian includes customizations that are designed to make the Raspberry Pi easier to use and includes many different software packages out of the box.

Raspbian is designed to be easy to use and is the recommended operating system for beginners to start off with their Raspberry Pi.

Debian

The Debian operating system was created in August 1993 by Ian Murdock and is one of the original distributions of Linux.

As Raspbian is based on the Debian operating system, it shares almost all the features of Debian, including its large repository of software packages. There are over 35,000 free software packages available for your Raspberry Pi, and they are available for use right now!

An excellent resource for more information on Debian, and therefore Raspbian, is the Debian administrator's handbook. The handbook is available at 

http://debian-handbook.info.

Open source software

The majority of the software that makes up Raspbian on the Raspberry Pi is open source. Open source software is a software whose source code is available for modification or enhancement by anyone. The Linux kernel and most of the other software that makes up Raspbian is licensed 

under the GPLv2 License. This means that the software is made available to you at no cost, and that the source code that makes up the software is available for you to do what you want to. The GPLV2 license also removes any claim or warranty. The following extract from the GPLV2 license preamble gives you a good idea of the spirit of free software:

"The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users….

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things."

Raspbian components

There are many components that make up a modern Linux distribution. These components work together to provide you with all the modern features you expect in a computer.
There are several key components that Raspbian is built from. These components are:
• The Raspberry Pi bootloader
• The Linux kernel
• Daemons
• The shell
• Shell utilities
• The X.Org graphical server
• The desktop environment

The Raspberry Pi bootloader

When your Raspberry Pi is powered on, lot of things happen behind the scene. The role of the bootloader is to initialize the hardware in the Raspberry Pi to a known state, and then to start loading the Linux kernel. In the case of the Raspberry Pi, this is done by the first and second stage bootloaders. The first stage bootloader is programmed into the ROM of the Raspberry Pi during manufacture and cannot be modified. The second and third stage bootloaders are stored on the SD card and are automatically run by the previous stage bootloader.

The Linux kernel

The Linux kernel is one of the most fundamental parts of Raspbian. It manages every part of the operation of your Raspberry Pi, from displaying text on the screen to receiving keystrokes when you type on your keyboard.

The Linux kernel was created by Linus Torvalds, who started working on the kernel in April 1991. Since then, groups of volunteers and organizations have worked together to continue the development of the kernel and make it what it is today.

If you want to use a hardware device by connecting it to your Raspberry Pi, the kernel needs to know what it is and how to use it. The vast majority of devices on the market are supported by the Linux kernel, with more being added all the time. 

A good example of this is when you plug a USB drive into your Raspberry Pi. In this case, the kernel automatically detects the USB drive and notifies a daemon that automatically makes the files available to you.

When the kernel has finished loading, it automatically runs a program called init. This program is designed to finish the initialization of the Raspberry Pi, and then to load the rest of the operating system. This program starts by loading all the 

daemons into the background, followed by the graphical user interface.

Daemons

A daemon is a piece of software that runs behind the scenes to provide the operating system with different features. Some examples of a daemon include the Apache web server, Cron, a job scheduler that is used to run programs automatically at different 

times, and Autofs, a daemon that automatically mounts removable storage devices such as USB drives.

A distribution such as Raspbian needs more than just the kernel to work. It also needs other software that allows the user to interact with the kernel, and to manage the rest of the operating system. The core operating system consists of a collection of programs and scripts that make this happen.

The shell

After all the daemons have loaded, init launches a shell. A shell is an interface to your Raspberry Pi that allows you to monitor and control it using commands typed in using a keyboard. Don't be fooled by this interface, despite the fact that it looks exactly like what was used in computers 30 years ago. The shell is one of the most powerful parts of Raspbian.

There are several shells available in Linux. Raspbian uses the Bourne again shell (bash) This shell is by far the most common shell used in Linux.

The Linux shell

Bash is an extremely powerful piece of software. One of bash's most powerful features is its ability to run scripts. A script is simply a collection of commands stored in a file that can do things, such as run a program, read keys from the keyboard, and many other things. Later on in this blog, you will see how to use bash to make the most from your Raspberry Pi.

Shell utilities

A command interpreter is not much of use without any commands to run. While bash provides some very basic commands, all the other commands are shell utilities. These shell utilities together form one of the important parts of Raspbian (essential as without the utilities, the system would crash). They provide many features that range from copying files, creating directories, to the Advanced Packaging Tool (APT) – a package manager application that allows you to install and remove 

software from your Raspberry Pi. We will discuss about APT later.

The X.Org graphical server

After the shell and daemons are loaded, by default the X.Org graphical server is automatically started. The role of X.Org is to provide you with a common platform from which to build a graphical user interface. X.Org handles everything from moving your mouse pointer, listening, and responding to your key presses to 

actually drawing the applications you are running onto the screen.

The desktop environment

It is difficult to use any computer without a desktop environment. A desktop environment lets you interact with your computer using more than just your keyboard, surf the Internet, view pictures and movies, and many other things. A GUI normally uses Windows, menus, and a mouse to do this.

Raspbian includes a graphical user interface called Lightweight X11 Desktop Environment or LXDE. LXDE is used in Raspbian as it was specifically designed to run on devices such as the Raspberry Pi, which only have limited resources.

Screenshot of LXDE desktop environment