/etc/apt/sources.list

cat /etc/apt/sources.list | grep -v "#" | grep .

cat /etc/apt/sources.list /etc/apt/sources.list.d/*
apt-cache policy

 sed -Ei 's/^# deb-src /deb-src /' /etc/apt/sources.list
apt update

Relevant configuration files and directories

• /etc/apt/sources.list: Configuration files with locations to fetch packages from.
• /etc/apt/sources.list.d/: directory with additional source list fragments.

Related terms

• apt update && apt upgrade
• do-release-upgrade, Focal
• apt-cache policy
• /etc/apt/apt.conf.d/
• apt-get source

See also

• apt-get [ install | upgrade | update | source ], /etc/apt/sources.list
• APT: wajig, apt-cache, add-apt-repository PPA, apt [ install | remove |purge | show | list | changelog | update | upgrade], do-release-upgrade, apt-mark, apt full-upgrade, sources.list, APT Automatic updates, unattended-upgrade, apt-transport-https, apt-get update, /etc/apt/, /etc/apt/apt.conf.d/50unattended-upgrades, /etc/apt/apt.conf.d/, /etc/apt/apt.conf.d/20auto-upgrades, apt-file, apt-utils

https://wiki.debian.org/SourcesList