• Skype and Ubuntu: green, black or scrambled video

    18 July 2011 Author: Stefano Prenna
    2 Comments

    A new beta version of Skype for Linux has been released some time ago (2.2.0.35) and is now available for download.

    Even if a couple of bugs have been fixed we are still missing a native 64-bits version and there are still issues with some webcams working fine under other applications but still showing black, green or scrambled output.

    One possible solution has been around for a while but I found a lot of poorly written/confusing posts.

    Basically it seems that even if Skype support the v4l2 programming interface, some driver implementations are not working fully with the standard.

    The one example is the gspca implementation found for some webcams (like the Logitech Quickcam IM/Connect or the Creative Webcam Instant) can work only if we force Skype to use the old v4l implementation by pre-loading the old library.

    The best way to do this is by creating a script that automatically pre-load the library and launches Skype (Ubuntu 32 bits):

    1. Install the libv4l-0 package:

    sudo apt-get install libv4l-0

    1b. If you have Ubuntu 64 bits you’ll have to install two packages:

    sudo apt-get install libv4l-0 lib32v4l-0

    2. Then use the following line to launch Skype:

    LD_PRELOAD=/usr/lib/libv4l/v4l2convert.so skype

    2b. if it doesn’t work, then look at the output in the terminal. If it is complaining about “error unexpected width / height in JPEG headerexpected: 320×240, header: 1600×1200” then try the following line:

    LD_PRELOAD=/usr/lib/libv4l/v4l2convert.so skype

    If you have Ubuntu 64 bits you’ll have to slightly change the two lines into:

    LD_PRELOAD=/usr/lib32/libv4l/v4l2convert.so skype

    LD_PRELOAD=/usr/lib32/libv4l/v4l2convert.so skype

    As pointed out by realmagnum, if you have Lubuntu 32bits, the line will have to be: LD_PRELOAD=/usr/lib/i386-linux-gnu/libv4l/v4l2convert.so skype

    3. Once you’ve found the line that works for you, create a new empty file, and put inside:

    #!/bin/sh
    LD_PRELOAD=/usr/libxx/xxxxxxx.xx skype

    4. chmod a+x filenameyou’vecreated

    Now everytime you’ll need to launch Skype, you’ll be able to do so (and use the webcam) by launching the script you’ve created!

  • Tutorial: How to remove/uninstall Gnome 3 in Ubuntu 11.04 (Natty Narwhal)

    31 May 2011 Author: Stefano Prenna
    23 Comments

    Natty

    Have you installed Gnome 3 from ppa:gnome3-team/gnome3 because you were tired of Unity or just because you wanted to test the new shell and this has broken your login? Are you now on the login screen but no graphic environment will ever work?

    Then you have to remove gnome 3 following the steps below:

    –         Press CTRL+ALT+F1 to access the terminal window and log in. At the prompt type following commands:

    –         sudo apt-get remove libgtk-3-common

    –         sudo apt-get install ppa-purge

    –         sudo ppa-purge ppa:gnome3-team/gnome3

    –         sudo apt-get dist-upgrade

    –         sudo apt-get install gnome-panel

    –         sudo apt-get install lightdm

    –         sudo shutdown –r now

    The pc will reboot and you should be able to use Unity/Classic login again.

    05/04/2013 *UPDATE* (thank you Anthony)!:

    If after the reboot the machine is not booting in Unity or Gnome3 and it’s just loading the terminal, maybe you’ll have to reconfigure lightdm to be the default login manager:

    –         sudo dpkg-reconfigure gdm

    You will see a window similar to this one (where you should then choose “lightdm”)

    gdm

     

     

     

     

     

     

     

     

    Good luck!

  • Tutorial: computer forensic analysis – how to recover lost or hidden data (on both Win/Ubuntu)

    19 May 2011 Author: Stefano Prenna
    No comment yet

    Magnifying Glass

    No matter what but if you work in the IT support business you will have to deal with user’s data. You will have some interesting tasks assigned like:

    1. Recover data from somebody else’s pc (Live Capture);
    2. Restore deleted data (Data reconstruction);
    3. Network Investigation;
    4. Wipe data.

    We need to remember that the machines we use in a corporate environment are property of the company which bought them. Even the data located on those machines are property of the same company. This means that you can receive some requests that look like something that should be done by a computer forensics expert.

    In this article I will list some of the most used freeware tools for both Windows and Linux to recover data from a forensic point of view.

    What we can recover?

    There are software available to recover almost every kind of file (images, music, video, documents like word, excel, etc).

    The basic idea is that every kind of file has one or more parts in common (like the header, just to give an example). This means that if we are looking for a specific kind of file we can use the right tool to not only undelete files, but to focus on the ones we really need and try to better recover the ones which have been partially overwritten.

    Headache

    From where we can recover?

    The options we have are basically two:

    1. Recover lost information from RAM (if the machine has not been turned off)
    2. Recover lost information from DISK (file has been deleted from OS)

    How do we recover?

    There are different toolsets, frameworks and even small freeware utilities available. Some of them are free others are quite expensive. I’ll put a small list here and I’ll try to cover each one of them in a different, specific article during the next days.

    Caine: www.caine-live.net/

    MDD: http://sourceforge.net/projects/mdd/

    The Volatility Framework: https://www.volatilesystems.com/default/volatility

    Windows Forensics Toolchest: http://www.foolmoon.net/security/wft/screenshots.html

    PTK: http://ptk.dflabs.com/

    Ocfa: http://sourceforge.net/apps/trac/ocfa

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