/etc/apt/sources.list.d  $ cat official-package-repositories.list 
# Do not edit this file manually, use Software Sources instead.

deb http://packages.linuxmint.com serena main upstream import backport #id:linuxmint_main
deb http://packages.linuxmint.com sonya main upstream import backport #id:linuxmint_main
deb http://packages.linuxmint.com sylvia main upstream import backport #id:linuxmint_main

deb http://archive.ubuntu.com/ubuntu xenial main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu xenial-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu xenial-backports main restricted universe multiverse

deb http://security.ubuntu.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://archive.canonical.com/ubuntu/ xenial partner

Так можно просмотреть репы

grep -Ev '^#|^$' /etc/apt/sources.list{,.d/*}