Apt-get error in Ubuntu - 'Something wicked happened resolving...'

The Apt-get command in Ubuntu is a powerful tool to install application into the Ubuntu system. However, you may get the following error when trying to use the apt-get install command.

>sudo apt-get install ruby
Err http://us.archive.ubuntu.com/ubuntu/ lucid/main ruby 4.2
Something wicked happened resolving 'us.archive.ubuntu.com:http' 
(-5 - No address associated with hostname) 
Failed to fetch
http://us.archive.ubuntu.com/ubuntu/pool/main/r/ruby1.8/ruby1.8_1.8.7.249-2_i386.deb

This error is caused because you have not setup the correct proxy setting in your apt.conf.

To fix this issue simply add the following line into your /etc/apt/apt.conf file as setting up the proxy in the export http_proxy env variable won't solve this issue.

> sudo /etc/apt/apt.conf
Then add the following line into
>Acquire::http::Proxy "http://username:password@proxy:8080";