This tutorial shows you how to download youtube videos using Terminal in Linux Operating System. First of all, you need to install youtube-dl for which enter this command in Terminal [You can get terminal by pressing CTRL + ALT+ T ]:

"sudo apt-get install youtube-dl" and then enter password.

Now, to download youtube video, just copy the video link which is in the format http://www.youtube.com/watch?v= .

Then open the terminal and type: youtube-dl "VIDEO LINK" and hit enter [For example: To download video of link http://www.youtube.com/watch?v=oNBBijn4JuY, youtube-dl "http://www.youtube.com/watch?v=oNBBijn4JuY"] Then your favorite video will start downloading.

This command generally downloads mp4 video which may take a longer time to download.
To download the youtube video in format of your choice, type "youtube-dl -F [VIDEO URL]" in the terminal. This shows all available video formats along with their size and resolution available for download.

Now, to download video in format of your wish type the following command in the terminal:

youtube-dl -F [FORMAT CODE] [VIDEO URL]

To download many youtube video at a time, create a file and place all the YouTube video links that you wish to download. Then enter following command in terminal:
youtube-dl -a youtube_links.txt

If you want to get full list of all the avialable options, enter man youtube-dl in terminal.

This is how you can download youtube videos in Linux OS.

Additional Info:

youtube-dl is a Python based small command-line tool that allows to download videos from YouTube.com, Dailymotion, Google Video, Photobucket, Facebook, Yahoo, Metacafe, Depositfiles, brightcove.com,auengine.com, RingTV, instagram.com, Jukebox, 3sat, CSpan, Statigr.am, traileraddict.com,hotnewhiphop.com, wat.tv, tu.tv, gamespot.com, tudou.com, Wimp.com, archive.org and break.com and many more similar sites.

Youtube-dl can be updated to the latest version using the following command.
youtube-dl -U