Enable system-wise HTTP proxy on debian

enable-proxy.sh

#!/bin/bash
# Idea taken from example: https://codepoets.co.uk/2014/debian-http_proxy-setting/

if [[ $EUID -ne 0 ]]; then
  echo "This script has to be executed as root" 1>&2
  exit 1
fi

if [ $# -ne 2 ]; then
  echo "Usage: ./enable-proxy.sh PROXY_IP PROXY_PORT"
  exit 2
fi

echo "export http_proxy=http://$1:$2" > /etc/profile.d/proxy.sh
echo "Acquire::http::Proxy \"http://$1:$2\";" > /etc/apt/apt.conf.d/99HttpProxy
echo "http_proxy = http://$1:$2" >> /etc/wgetrc
echo "System-wise proxy set to $1:$2"

To install a proxy server with squid on CentOS 7 (I assume you have root access):

yum install squid
sed -i 's/http_access deny all/http_access allow all/g' /etc/squid/squid.conf
systemctl start squid
systemctl enable squid

Add this to /etc/sysconfig/iptables:

-A INPUT -p tcp -m tcp --dport 3128 -j ACCEPT

and then execute:

systemctl restart iptables