Autostarting a browser on the Raspberry Pi

In this tutorial, I’ll show you how to start a browser after booting on the raspberry pi.

  1. Disable login
    In case you want the browser to start without having to log in, apply the following steps:

    sudo vi /etc/inittab

    Comment this line …

    1:2345:respawn:/sbin/getty 115200 tty

    … like this.

    #1:2345:respawn:/sbin/getty 115200 tty1

    Add the following line:

    1:2345:respawn:/bin/login -f pi tty1 </dev/tty1 >/dev/tty1 2>&1

    Save and exit vi with :wq.

  2. Start X server after boot
    Edit this file:

    sudo vi /etc/rc.local

    And add the following line before the line ‘exit 0’.

    su -l pi -c startx

    Save and quit vi.

  3. Autostarting bash script
    Let’s create a bash script that should be executed after startup. Here we shall place the command to execute the browser. Of course, you can extend this script as you like.

    vi /home/pi/

    Now add the following code to start the browser midori in fullscreen mode pointing at the adress

    midori -e Fullscreen -a &

    Make your bash script executable.

    sudo chmod +x /home/pi/

    Add the script execution to your LXDE autostart file.

    sudo vi /etc/xdg/lxsession/LXDE/autostart

    Add the line

    @sh /home/pi/

    That’s it! You’re good to go. Try rebooting.

  4. Optional steps
    You may notice your screen going black or a screensaver starting which might not be what you want for your application. Luckily, you can change this in a few easy steps.
    Install the package x11-xserver-utils.

    sudo apt-get install x11-xserver-utils

    Now edit the autostart file again. Uncomment the screensaver and add a few lines. Your file should look something like this.

    @lxpanel --profile LXDE
    @pcmanfm --desktop --profile LXDE
    #@xscreensaver -no-splash
    @xset s off
    @xset -dpms
    @xset s noblank
    @sh /home/pi/

    Your screen should stay on permanently.
    If you would like to hide the mouse, install the tool unclutter and add the following line to the top of the

    unclutter -idle 5 &



Installing Cloudera’s Hadoop Distribution CDH4 to a Virtual Machine

In this post I shall explain how to install Cloudera’s Hadoop distribution CDH4 to a virtual machine running Ubuntu 12.04 LTS from scratch. The second part can be used to install Hadoop natively to you Ubuntu 12.04 installation. However, this tutorial was written with a development or experimental environment in mind.


  1. A Computer with at least 4GB of RAM (8GB+ recommended), as the virtualization of Hadoop consumes a lot of memory.
  2. 64 bit processor with activated Hardware virtualisation in BIOS (If you don’t have a 64 bit processor, you won’t be able to use Ubuntu with CDH 4 and have to choose another OS)

 Virtual machine installation:

  1. Download the .iso-file for Ubuntu 12.04 LTS 64 bit from
  2. Next, download Virtualbox for your host operation system, e.g. Windows 7. The host operating system is the system running Virtualbox, whereas the virtual operating system is called guest system.
    You will find the binaries for your specific operating system with further installation instructions at
  3. After installation, open Virtualbox and create a new virtual machine. Call it Ubuntu Hadoop or any other name and select Linux, Ubuntu 64bit as operating system.
  4. In the next step, you will have to create a new virtual hard disk. I’d recommend a minimum of 20GB in VDI format with dynamic allocation. Dynamic allocation means that the file on your host disc won’t be a fixed size but will grow with the hard disc of the guest system. However, it will be limited to a fixed size, i.e. 20GB. Initially this will be slower than a fixed size disc, while consuming less space on the host system.
  5. Once you have created the virtual machine, start your virtual machine by double clicking on the name. You can now choose the downloaded Ubuntu .iso-file as start disk.
  6. This will open the Ubuntu installer. Follow the on screen instructions to install Ubuntu to the virtual machine. Visit the Ubuntu Homepage for further help with the installation.

Prerequesites to installing CDH4

  1. Install open ssh server package.
    sudo apt-get install openssh-server
  2. Set a password for root. WARNING: This is only set for this virtual machine. In production environments, this could present a security risk.
    sudo passwd
  3. Edit /etc/hosts in a editor with root privileges. Uncomment the second line. It should look something like this.    antony-VirtualBox localhost
    #    antony-VirtualBox
    # The following lines are desirable for IPv6 capable hosts
    #::1     ip6-localhost ip6-loopback
    #fe00::0 ip6-localnet
    #ff00::0 ip6-mcastprefix
    #ff02::1 ip6-allnodes 
    #ff02::2 ip6-allrouters

Installing Cloudera Hadoop Distribution (CDH4)

  1.  Go to and locate Products – CDH. Click ‘Download and Install CDH 4’. On the next page, click ‘Download and Install CDH 4 automatically’. On the following page, under Cloudera Manager 4.1.1, click ‘download‘. Save the .bin-file to disk.
    Cloudera Homepage
  2. Make the installer executable and run it as root.
    chmod u+x ./cloudera-manager-installer.bin
    sudo ./cloudera-manager-installer.bin
  3. Accept the licenses and follow the on-screen instructions. It is important to be patient! The installer may seem to have crashed at times, however, it simply takes its time to install. At the end of the installation a browser should open.
  4. Log in with the credentials ‘admin’, ‘admin’.
  5. You can now add hosts to your cluster by clicking ‘Hosts’ and then add hosts. Enter localhost or as IP. In the process you can choose whether to install YARN or MRv1. Be sure to select the latter.
  6. After the installation and configuration of your cluster, you can access your running services under ‘services’.
  7. You have successfully installed a one-node cluster on the virtual Ubuntu machine.

Using counters in Hadoop MapReduce

Sometimes when running MapReduce jobs, you want to know whether or how often a certain event has occured during execution. Imagine an iterative algorithm that should run until no changes were made to the data during execution. Let’s assume that the change happens in the map function.

A common mistake would be to use the context object and set a value in the configuration object.

context.getConfiguration().set("event", "hasOccured");

This approach only works when executing the job on a single machine. When running on a cluster of computers each mapper or reducer will have its own configuration object. Therefore, global reading and writing is not possible. It can only be used to store information before executing the job and passing this information to the mappers and reducers, e.g. filenames of auxiliary files, etc.

In order to know how often a mapper has changed a data item on a global level, we will use a so-called counter. First you have to define an Enum which represents a group of counters. In this example we will only have one counter.

public enum MyCounters {

From within the map method of our mapper, we can access the counter and increment it when we change a dataset.The counter is identified by the enum value.


Finally, we can read the counter after job execution and see whether the data has changed.


All counters are displayed during job execution.

Summary: Counters are a useful feature provided by the hadoop framework to globally certain values during job execution. They can also be analyzed to count how many damaged or malformed datasets were in the input data.

Benchmark your hard disk in Ubuntu

If you want to compare your hard disk speeds in Ubuntu 11.10, you can do this in three easy steps:

  1. Start the programme ‘Disk Utility’.
  2. Select the desired hard disk you want to test and hit ‘benchmark’.
  3. Compare the results. Here I’m comparing an old conventional hard disk drive to my new SSD drive. As expected, you notice a huge difference in speed.