To configure the proxy in Ubuntu you can set it in different places:

apt

In order to use apt with a proxy you have to edit the /etc/apt/apt.conf file with the following:

Acquire::http::proxy "http://username:password@host:port/";
Acquire::ftp::proxy "ftp://username:password@host:port/";
Acquire::https::proxy "https://username:password@host:port/";

Environment Variables

To add the proxy as an environment variable, edit the /etc/environment file with the following:

http_proxy=http://username:password@host:port/
ftp_proxy=ftp://username:password@host:port/
https_proxy=https://username:password@host:port/

gtk3 programs

For gtk3 programs, use the proxy settings in network settings.

I got the information from: [https://www.quora.com/How-do-I-set-the-proxy-setting-using-Linux-command-line-on-Ubuntu-14-04]