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.

Post-installation commands...

I have been a big fan of Fedora but those days I gave a try to Ubuntu 11.04 (Beta2). I like the way how Ubuntu manages packages since it looks very clean and stable although it's a Beta [2] release.

I was playing around with new packages and some updates ('apt-get dist-upgrade') which provoke a unstable system so a couple re-installations have been necessary. After every re-installation I executed the following commands:

1. sudo software-properties-gtk, the Ubuntu's mirror for Colombia is not synchronized and the 'apt-get update' procedure throws some errors. Through this command, I could change the Colombia Mirror for the 'Main Server' option.
2. gnome-window-properties, this command allows to modify the current windows behavior e.g. 'Select windows when the mouse mover over them' and Roll up window on the 'Double-click titlebar' event happens.

Give a try to Ubuntu 11.04, it's cool and fast.

PS: Fedora guys, why are you looking for a code name for Fedora 16 when Fedora 15 has not been released yet. Awkward, ah?

Ubuntu 11.04 Beta

Last week, I installed Ubuntu 11.04 Beta on my laptop. My Linux box exhibits a better performance during the login procedure.
Despise the new graphical environment is dramatically different, the learning curve is not so steep.
I'm a Latex user and some additional packages were needed for a fully operational environment

• texlive-latex-base
• latex-beamer
• texlive-fonts-recommended

OK, unexpectedly [g]vim was not installed, so vim-gtk package was also installed by hand.