Apt-Get List Installed – step by step tutorial. Apt is a command-line interface that allows you to perform actions such as installing new software packages, removing unnecessary software packages, updating the existing software packages, searching for specific software packages etc. on a Linux VPS running Debian as an operating system or Debian-based Linux distributions like Ubuntu. In this tutorial, we will show you how to list all installed packages with apt on Ubuntu (show all installed software on your VPS).