Ubuntu & Debian sources.list

Ubuntu Generic:
cp /etc/apt/sources.list /etc/apt/sources.list.bak && curl -s http://mark99.ru/apt-focal.txt | sed "s/focal/$(lsb_release -c -s)/g" > /etc/apt/sources.list

Ubuntu 20.04:
curl -o /etc/apt/sources.list http://mark99.ru/apt-focal.txt
wget -O /etc/apt/sources.list http://mark99.ru/apt-focal.txt

Debian Stable:
curl -o /etc/apt/sources.list http://mark99.ru/apt-debian-stable.txt
wget -O /etc/apt/sources.list http://mark99.ru/apt-debian-stable.txt