The Raspberry Pi is an exciting device that will hopefully bring computer programming (and Linux) to the masses. The low-priced, single-board computer features 256MB of RAM, a 700MHz ARM processor and a powerful GPU capable of 1080p video playback at 30fps and 3D graphics performance comparable to that of the original Xbox games console.
The idea behind the Raspberry Pi is to provide a computing environment where children can have the freedom to program without having to worry about the consequences of possibly breaking the family computer.
The device has also gained a lot of attention from the hacker community. Want a low-powered, low-cost web server, media centre, or SSH client? Then this could be exactly what you’re looking for. Throw in a network switch and you could have a cluster! The possibilities are virtually endless.
As you might imagine, the Raspberry Pi is a specialised hardware platform, similar to that of a smartphone. For this reason, operating systems are provided as images that are flashed to an SD card. There are currently three Linux flavours for the device: Debian, Fedora and Arch Linux. Debian is our recommended distribution out of the three on offer, and will be the one used in these tutorials.
By this point, you’re probably dying to rip the Pi out of the box and get started, so let’s do it!
01 Download the latest Debian image
Head over to the Downloads section of RaspberryPi.org and download the latest Debian root file system. The image can be downloaded via HTTP download or torrent. The Debian image is roughly 800MB and about 2GB when extracted, so make sure you have enough space free available.
02 Download the SHA-1 checksum
We want to verify the image we just downloaded before we carry on. You need to select the direct download option on the download page to get to the load balancer page. Once you’re there, right click on the SHA‑1 checksum hyperlink and select the option to save the link. Save the file in the same location you saved the Debian ZIP file.
03 Start your terminals
Check your current location using the pwd command. To list the files in the current directory, use the ls command. Use the cd command to navigate to where you saved the image. You can use cd.. to go back a directory. Once you’re in the correct directory, use ls to list the files and check they are both present.
04 Verifying the image
Use the sha1sum command with the following syntax: ‘sha1sum –check [sha1 file]’. Our file was debian6-17-02-2012.zip.sha1. The command may take a few minutes to run and you’ll get a result when it’s finished. If the result is okay, you can carry on. If not, go back to step 1!
05 Extract the Debian image
We now need to extract the image from the ZIP file. To do this, we’ll be using a tool called unzip. You may need to use your package manager to install it if it’s not already on your system. To extract the image, use the unzip command with the following syntax: ‘unzip [zip file]’. In our case, the command was ‘unzip debian6-17-02-2012.zip’. Once the command has finished, use ls to verify that a new folder has been created. This folder will contain the image file.
06 Connect your card reader
Insert your SD card into your card reader and connect it up to your PC if you’re using a USB reader rather than an internal reader. Decline any offers to view the contents of the SD card as we’re still working from the terminal.
07 Locate your SD card
We now need to find the path to your SD card because it could be disastrous if dd was used on the wrong device. We’ll be using the command ‘fdisk -l’. Fdisk requires root privileges so you’ll either need to use the command ‘sudo fdisk -l’ or switch to root using the su command before running ‘fdisk -l’. The ‘fdisk -l’ command simply lists each disk attached to your computer. The SD card we used was 8GB in capacity. There is a disk in our ‘fdisk –l’ output with a capacity of 8068MB, so that must be our SD card. The path to our SD card is /dev/sdb. Make note of yours as you’ll be using it in the next couple of steps.
08 Writing the image to your SD card
Start by using the cd command to change into the directory where the Debian image was extracted. This next part can break your system if you write to the wrong storage device with dd, so check and check again! As with fdisk, the dd command requires root privileges so you either need to start the following commands with sudo or switch to root using su before running them. Use the dd command with the syntax:
dd bs=1M if=[debian .img file] of=[path to your SD card]
In our case, the command was: ‘dd bs=1M if=debian6-17-02-2012.zip of=/dev/sdb’. dd doesn’t display a progress bar but no news is good news in this case. You’ll see a summary of the transfer once the command is finished.
09 Disconnect and reconnect
Before continuing, disconnect and then reconnect your SD card reader to ensure that the kernel has reloaded the newly flashed partition structure.
10 Start up GParted
The Debian image currently only takes up 2GB of space on the SD card, so we need to use GParted to resize the partitions so that we can make use of the full capacity on the card. You may need to install GParted using your package manager if you don’t already have it on your system. Start GParted and make sure that your SD card is selected in the combo box on the top right of the window.
11 Resize your partitions
Use the Resize/Move tool to move the linux-swap partition to the end of the SD card and then resize the main ext4 partition to fill up the space all the way up to the linux-swap partition. You should have two pending operations once you have done this.
12 Apply the changes
Once you’re happy with the new partition layout (making sure you have not moved the FAT32 partition) you can go ahead and click the apply button, which will write the changes to your SD card. The command may take a couple of minutes to complete, so be patient.
13 Connect it up!
Start by inserting your SD card; the gold connectors should be facing upwards as you insert it with the board’s processor facing you. Then connect your USB keyboard and mouse. Connect your display via HDMI or composite. Finally, connect your Ethernet cable; you can use the Pi without one but you’ll have no internet connection to install more packages, and your time and date will have to be set manually (as the device has no battery-powered clock). There’s no power button, so power it on by connecting the micro-USB cable. Notice the cardboard that the Pi is placed on; we wouldn’t want it sitting on any conductive metals now, would we?
14 Log in
The username and password for the image are on the download page. In this case, the credentials are pi/suse. Once you’re logged in, you’ll want to type ‘startx’ to get into LXDE.
15 Set the date & time
This step is only necessary if you’re not using Ethernet, or NTP isn’t getting the correct time for you. Start LXTerminal by going to Menu>Accessories>LXTerminal. Use the date command with a similar syntax to:
sudo date --set “23 APR 2012 16:01”
16 GPU memory allocation
The GPU on the Raspberry Pi shares RAM with the device. There are three different firmware files on the FAT32 partition, each giving a different amount of RAM to the GPU. The allocation you choose depends on what task you want to do on the device. The default for this image is that the GPU uses 64 out of 256MB. There are also options for 32MB and 128MB out of 256MB. The FAT32 partition is mounted in the /boot folder on the Raspberry Pi. To change the GPU’s memory usage, copy the appropriate firmware file with the name start.elf, overwriting the file that is currently there. You’ll have to restart the device for the changes to take effect.
17 Introducing Python
We’re going to finish off by creating a small ‘Hello World’ application in Python. Start LXTerminal again and use the touch command to create a new file called hello_world.py. Mark the file as executable using the command:
chmod +x hello_world.py
18 Hello, World
Open hello_world.py in the nano editor by typing nano. Start by typing the shebang symbol (#!), followed by the path to Python. Use the Return key to add blank line and then add a comment explaining what the application will do:
#! /usr/bin/python # Our first Hello Word on the Raspberry Pi!
We want the application to sleep so we can admire our work. We need to import the time library to do this. Use the print function to output some Hello World text, enclosing the text in quotation marks. Don’t forget to use comments! Using print with empty quotation marks simply outputs a blank line.
20 Sleeping continued
Use the print function to output that the program is going to sleep for five seconds. Then use the time.sleep function, specifying the time in seconds, to make the program sleep.
print ("Sleeping for 5 seconds") time.sleep (5)
21 Finishing off
Finish your first program off by printing a new line and then printing that the program will exit. The program will simply end when it reaches the last command, which in this case will be ‘print(“Exiting…”)’:
#Print another new line print("") print("Exiting...")
22 Saving our work
We save files in nano using Ctrl+O. Press Enter after pressing Ctrl+O to save the output into the hello_world.py file we created earlier. Then you can use Ctrl+X to exit nano.
23 Running our first program
Type ‘./hello_world’ into the terminal and watch your first program run. The ./ directive attempts to execute anything that comes after it. Once you’re finished, close the terminal by typing ‘exit’.
24 Powering off
We still have to turn the Raspberry Pi off nicely, regardless of it having a power button or not. Yanking the power cable could cause data corruption and we don’t want that. Go the LXDE menu and select ‘logout’. Wait for the system to halt fully before removing the power cable.