Export Command for Proxy Environment Variables

Use the following commands to configure your proxy for http and ftp traffic on the command line
export http_proxy= export ftp_proxy=

If your proxy requires login/authentication, you can use the format:
export http_proxy=

To have this applied every time you log in, place these lines in your .bashrc in your home (~) directory.
export http_proxy=
export ftp_proxy=

Network Proxy Settings

For GNOME, go to Computer->Desktop Preferences->Network Proxy
For KDE desktop manager, you can get to the network proxy settings under System Settings > Network Settings > Proxy

In the setting, you can configure either by your proxy server and port, by the network, or a file via a URL/file location (e.g. ) .

These settings work with most other applications (e.g. other browsers like Chrome, OS commands).

Program/Application Level

Some applications and commands need to be configured individually. Below are some common examples.

Firefox

You can manually set up the Firefox proxy in Options menu. Go to Options > Advanced > Settings.

Fedora – Yum Package Manager

yum proxy settings can be found in the file system at
/etc/yum.conf

Add a line to the file with the following information:

Source: justintung.com