visudo

Defaults env_reset

Defaults env_keep = "http_proxy ftp_proxy"

Defaults env_keep = "http_proxy https_proxy ftp_proxy DISPLAY XAUTHORITY"

ubuntu@ubuntu:~$ cat /etc/apt/apt.conf
Acquire::http::Proxy "http://Username:Password@proxy.foo.bar.edu.au:8080";

ubuntu@ubuntu:~$ cat /etc/apt/apt.conf.d/05proxy
Acquire::http::Proxy "http://Username:Password@proxy.foo.bar.edu.au:8080";

export http_proxy=http://proxyusername:proxypassword@proxyaddress:proxyport
sudo apt-get update

sudo http_proxy=http://yourserver apt-get update

Acquire::http::proxy "http://user:password@host:port/";