Learning Raspbian: Get up and running with Raspbian and make the most out of your Raspberry Pi

The Raspberry Pi Foundation is a not-for-profit charity and was founded in 2006 by Eben Upton, Rob Mullins, Jack Lang, and Alan Mycroft. The aim of this charity is to promote the study of computer science to a generation that didn't grow up with the BBC Micro or the Commodore 64.

They became concerned about the lack of devices that a hobbyist could use to learn and experiment with. The home computer was often ruled out, as it was so expensive, leaving the hobbyist and children with nothing to develop their skills with.

Graphics in the Raspberry Pi are provided by a Videocore 4 GPU. The graphic performance of the graphics processing unit (GPU) is roughly equivalent to the Xbox, launched in 2011, which cost many hundreds of dollars. These might seem like very low specifications, but they are enough to play Quake 3 at 1080p and full HD movies.

There are two ways to connect a display to the Raspberry Pi. The first is using a composite video cable and the second is using HDMI. The composite output is useful as you are able to use any old TV as a monitor. The HDMI output is recommended however, as it provides superior video quality. A VGA connection is not provided on the Raspberry Pi as it would be cost prohibitive. However, it is possible to use an HDMI to VGA/DVI converter for users who have VGA or DVI monitors.

The Raspberry Pi also supports an LCD touchscreen. An official version has not been released yet, although many unofficial ones are available. The Raspberry Pi Foundation says that they expect to release one this year.

The Raspberry Pi has several different variants: the Model A and the Model B. The Model A is a low-cost version and unfortunately omits the USB hub chip. This chip also functions as a USB to an Ethernet converter. The Raspberry Pi Foundation has also just released the Raspberry Pi Model B+ that has extra USB ports and resolves many of the power issues surrounding the Model B and Model B USB ports.

Parameters	Model A	Model B	Model B+
CPU	BCM2835	BCM2835	BCM2835
RAM	256 MB	512 MB	512 MB
USB Ports	1	2	4
Ethernet Ports	0	1	1
Price (USD)	~$25	~$35	~$35
Available since	February 2012	February 2012	July 2014
Boards

Differences between the Raspberry Pi models

The success of the Raspberry Pi has encouraged many other groups to design accessories for the Raspberry Pi, and users to use them. These accessories range from a camera to a controller for an automatic CNC machine. Some of these accessories include:

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.

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:

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 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.

The Linux logo is a penguin named Tux:

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.

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.

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.

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 book, you will see how to use bash to make the most from your Raspberry Pi!

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.

You will learn more about APT later in this book.

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.

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.

Later in this book, you will learn how to customize and use LXDE to make the most of your Raspberry Pi.

A screenshot of the LXDE desktop environment