Focus follows mouse for Unity

Something that I love from X window systems is the possibility to activate a window with no click on it. However, Unity and Gnome 3 by default do not make accessible this feature. I googled how to activate the "focus follows mouse" feature and I found this link. I typed these commands and now the feature is back ;-)

gconftool-2 --type string --set /apps/metacity/general/focus_mode mouse
gconftool-2 --type boolean --set /apps/metacity/general/auto_raise false

"apt-get upgrade" "packages have been kept back"

I have deactivated the automatic upgrade process in my Ubuntu box then every one or two week I execute the following steps,

sudo apt-get update
sudo apt-get upgrade

However, today during the upgrade process I got this message:

Reading package lists... Done
Building dependency tree      
Reading state information... Done
The following packages have been kept back:
  linux-generic linux-headers-generic linux-image-generic
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.

I didn't understand why this happened so I googled and I found this link where it explains that "the packages that have newer versions available, and install any new dependencies which are required to do that." Then for fixing this, just run the "apt-get dist-upgrade" command.

How to find the window id in xorg

Execute "xwininfo", that's it.

Preseeding files for automatic installation of Linux systems

Days ago, I found an interesting link which explains how to install Linux systems answering no questions. This procedure doesn't require any particular CD, you can use your regular installation CD along with a text file where answers to the usual questions for installing a Linux system are responded.

The original link can be found here and additional information about content of preseeding files can be obtained from here and here.

This procedure is a blessing when you frequently install Linux systems.

This procedure was initially implemented for RedHat systems but it was later extended to Ubuntu systems. The preseeding file and variables defined in it are release dependent, for instance a preseeding file for lucid may not work oneiric.

Finally, if you wan additional info, this kind of procedure is also referred as "preconfiguration file", "preseeding file" and "installcdcustomization".

Error in API call to delete - Vagrant

These days, I'm heavily working with Vagrant and Chef. During my working sessions, I created several scripts then run "vagrant up", scripts fail then "vagrant destroy" then do some modifications, run "vagrant up" again and this loop occurs for many times. Suddenly, "vagrant up" doesn't run but arises this message:

[node1] Destroying VM and associated drives...
/var/lib/gems/1.8/gems/virtualbox-0.9.1/lib/virtualbox/com/implementer/ffi.rb:106:in `call_and_check': Error in API call to delete: 2147944126 (VirtualBox::Exceptions::COMException)
    from /var/lib/gems/1.8/gems/virtualbox-0.9.1/lib/virtualbox/com/implementer/ffi.rb:80:in `call_vtbl_function'

Looking into log files (${HOME}/.VirtualBox), I found that for an unknown reason "vagrant destroy" can not delete the directory which contains the disk attached to the virtual machine.  Solution: erase that directory by hand. Problem solved!

extracting audio content from video files with open source tools

These days, I have downloaded many music videos and I have enjoyed them but I don't only want to watch them but also listen them. I looked in Internet and found this interesting link which give many tips about how to transform and extract information from multimedia files using ffmpeg.

Then, I created this bash script which extracts audio content from music videos.

#!/bin/bash
OUTPUT=""
if [ $# = 1 ] ; then
    OUTPUT=${1%.*}.mp3
elif [ $# = 2 ] ; then
    OUTPUT=${2}
else
    echo "Usage:"
    echo "     ${0} video_filename output.mp3"
    exit
fi
/usr/bin/ffmpeg -i "${1}" -vn -ar 44100 -ac 2 -ab 192 -f mp3 "${OUTPUT}"

Cut and paste it into your preferred editor (VI). This link explains how to retrieve just the file name without its extension.

Getting high resolution images from PDF files

Today I was preparing a lecture for Thursday (I guess) and I found very illustrative images from a PDF book but I got some problems for extracting them from the book.

• Acroread (for Linux) didn't keep the image in the clipboard 
• The "convert" tool (from Imagemagick) by default, made a poor conversion from PDF to any format

I searched in Internet and I found these two links that gave me a clue

• http://ardvaark.net/useful-pdf-imagemagick-recipes
• http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=11476

For my needs "convert -density 300 pdffile.pdf image.png" did the trick. The image.png file gave me an excellent resolution. From that point, I used gimp for cropping the region that I need.