Using apt-get with a proxy server
Linux users often want to install new software and updates or upgrade their systems through the apt-get command but they are unable to do anything because of a connection error that occurs even if the Internet connection is working well. This happens particularly when you use the Internet from behind a proxy server. Here is a tip to overcome this issue—add details about the proxy server to apt.conf.
Open the file /etc/apt/apt.conf in a text editor and add the lines as shown below: