How to set proxy for apt-get in Ubuntu

Http::Proxy is the default http proxy to use.

The standard form is http://[[user][:pass]@]host[:port]/."

In other words, create an /etc/apt/apt.conf file and in it put
something like this:

ACQUIRE {
http::proxy "http://user:password@proxy:8080/"
}


for example, without proxy authenication, it should be something like

ACQUIRE {
http::proxy "http://172.31.1.3:8080/"
}