[Justice_mybb_import8175]

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*Image*
The above link shows that Ubuntu 12.04-LTS currently does not have Aircrack-ng in it's default Repositories.
You might want to edit your tutorial to reflect this by pointing users of Linux to the Aircrack-ng PPA for Launchpad or a suitable alternative PPA for it mate.
Just to avoid any confusion for those who might discover that the hard way.
Footnote: Staff is free to delete this comment after Mr.Grayhat has reflected this in his tutorial should he choose to.

Thank you Linuxephus, I did not know that. To make things clear on Ubuntu 12.10 you can install aircrack-ng by typing "apt-get install aircrack-ng", Backtrack already has aircrack-ng installed so no need to type the code unless you want to update it.