Sources.list

sources.list resides in /etc/apt/ on systems that use the APT package manager (Debian, Ubuntu...).

Debian

Bullseye

deb http://deb.debian.org/debian/ bullseye main non-free contrib
deb-src http://deb.debian.org/debian/ bullseye main non-free contrib

deb http://deb.debian.org/debian/ bullseye-updates main non-free contrib
deb-src http://deb.debian.org/debian/ bullseye-updates main non-free contrib

deb http://security.debian.org/debian-security bullseye-security main non-free contrib
deb-src http://security.debian.org/debian-security bullseye-security main non-free contrib

# Optional: backports
deb http://deb.debian.org/debian bullseye-backports main

Read more about Debian Backports.