user@server:~$ sudo apt dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
  ubuntu-advantage-tools
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
user@server:~$ grep "^deb\ " -r /etc/apt/ --include=*.list
/etc/apt/sources.list.d/certbot-ubuntu-certbot-xenial.list:deb http://ppa.launchpad.net/certbot/certbot/ubuntu xenial main
/etc/apt/sources.list.d/ondrej-ubuntu-php-xenial.list:deb http://ppa.launchpad.net/ondrej/php/ubuntu xenial main
/etc/apt/sources.list:deb http://ca.archive.ubuntu.com/ubuntu/ xenial main restricted
/etc/apt/sources.list:deb http://ca.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
/etc/apt/sources.list:deb http://ca.archive.ubuntu.com/ubuntu/ xenial universe
/etc/apt/sources.list:deb http://ca.archive.ubuntu.com/ubuntu/ xenial-updates universe
/etc/apt/sources.list:deb http://ca.archive.ubuntu.com/ubuntu/ xenial multiverse
/etc/apt/sources.list:deb http://ca.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
/etc/apt/sources.list:deb http://ca.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu xenial-security main restricted
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu xenial-security universe
/etc/apt/sources.list:deb http://security.ubuntu.com/ubuntu xenial-security multiverse