Debian set proxy

Edit /etc/profile.d/proxy.sh, add

export http_proxy=http://192.168.0.1:3128
export https_proxy=http://192.168.0.1:3128
export ftp_proxy=http://192.168.0.1:3128

Edit /etc/apt/apt.conf.d/99HttpProxy, add

Acquire::http::Proxy "http://192.168.0.1:3128";
Acquire::https::Proxy "http://192.168.0.1:3128";
Acquire::ftp::Proxy "http://192.168.0.1:3128";

Edit /etc/wgetrc, add

http_proxy = http://192.168.0.1:3128
https_proxy = http://192.168.0.1:3128
ftp_proxy = http://192.168.0.1:3128

Edit /etc/environment

export http_proxy=http://192.168.0.1:3128
export https_proxy=http://192.168.0.1:3128
export ftp_proxy=http://192.168.0.1:3128

some system commands rely on wget, and may not otherwise use an environment variable, e.g. debootstrap; the http_proxy setting should be present by default but commented out.

This is all, in a round about way, relayed to the http proxy security vulnerability announced in July 2016 – see httpoxy.org for more info.