This document provides instructions for installing update tools and configuring apt package sources on a Debian system. It lists curl, wget, apt-transport-https and dirmngr as packages to install for updating and editing /etc/apt/sources.list to add Debian oldstable, oldstable-updates, and security repositories as well as a backports repository for fetching newer package versions.

1. Install for update
apt install curl wget apt-transport-https dirmngr
nano /etc/apt/sources.list
add the following:
deb http://deb.debian.org/debian/ oldstable main contrib non-free
deb-src http://deb.debian.org/debian/ oldstable main contrib non-free
deb http://deb.debian.org/debian/ oldstable-updates main contrib non-free
deb-src http://deb.debian.org/debian/ oldstable-updates main contrib non-
free
deb http://deb.debian.org/debian-security oldstable/updates main
deb-src http://deb.debian.org/debian-security oldstable/updates main
deb http://ftp.debian.org/debian jessie-backports main
deb-src http://ftp.debian.org/debian jeesie-backports main