Tentei o seguinte com o Ubuntu 18.04 biônico e funciona:
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic main restricted
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic universe
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-updates universe
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-updates multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic main restricted
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic universe
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-updates universe
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic multiverse
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-updates multiverse
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-amd64 http://security.ubuntu.com/ubuntu bionic-security main restricted
deb-amd64 http://security.ubuntu.com/ubuntu bionic-security universe
deb-amd64 http://security.ubuntu.com/ubuntu bionic-security multiverse
deb-i386 http://security.ubuntu.com/ubuntu bionic-security main restricted
deb-i386 http://security.ubuntu.com/ubuntu bionic-security universe
deb-i386 http://security.ubuntu.com/ubuntu bionic-security multiverse
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic main/debian-installer restricted/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-updates main/debian-installer restricted/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-updates universe/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic multiverse/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-updates multiverse/debian-installer
deb-amd64 http://archive.ubuntu.com/ubuntu/ bionic-backports main/debian-installer restricted/debian-installer universe/debian-installer multiverse/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic main/debian-installer restricted/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-updates main/debian-installer restricted/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-updates universe/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic multiverse/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-updates multiverse/debian-installer
deb-i386 http://archive.ubuntu.com/ubuntu/ bionic-backports main/debian-installer restricted/debian-installer universe/debian-installer multiverse/debian-installer
deb-amd64 http://security.ubuntu.com/ubuntu bionic-security main/debian-installer restricted/debian-installer
deb-amd64 http://security.ubuntu.com/ubuntu bionic-security universe/debian-installer
deb-amd64 http://security.ubuntu.com/ubuntu bionic-security multiverse/debian-installer
deb-i386 http://security.ubuntu.com/ubuntu bionic-security main/debian-installer restricted/debian-installer
deb-i386 http://security.ubuntu.com/ubuntu bionic-security universe/debian-installer
deb-i386 http://security.ubuntu.com/ubuntu bionic-security multiverse/debian-installer
clean http://archive.ubuntu.com/ubuntu
clean http://security.ubuntu.com/ubuntu