Here is my sources list:
deb http://ports.ubuntu.com/ubuntu-ports/ xenial main restricted
deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial main restricted
deb http://ports.ubuntu.com/ubuntu-ports/ xenial-security main restricted
deb http://ports.ubuntu.com/ubuntu-ports/ xenial-updates main
deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-updates main restricted
deb http://ports.ubuntu.com/ubuntu-ports/ xenial multiverse
deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial multiverse
deb http://ports.ubuntu.com/ubuntu-ports/ xenial-updates multiverse
deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-updates multiverse
deb http://ports.ubuntu.com/ubuntu-ports/ xenial universe
deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial universe
deb http://ports.ubuntu.com/ubuntu-ports/ xenial-updates universe
deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-updates universe
deb-src http://archive.canonical.com/ubuntu trusty partner