Linux: inventory a server (services, ports, logs)

The contractor who ran the ERP server left three weeks ago, without handing anything over. Nobody knows what runs on it, or what would come back on its own after a power cut. Management is not asking you to fix anything: they want a written inventory, so that the next incident is not handled blind. You start from a shell and nothing else. It is the situation almost every system administrator starts with, and the one no course prepares you for. The guide does not give you the answers: it gives you the questions and the tools, and you search the machine before opening the solution. You will learn to read the file tree to separate what a package installed from what a human put there by hand, to ask systemd which unit a process belongs to, and to put a name on every listening port. Along the way, you will come across what every inherited server hides: business data no standard backup would take, a program nobody watches, and a script that works by hand but would fail as a service. You fix nothing, you document. Your inventory is read on the machine at the end of the lab, and it counts for your ranking. A real server, with its services in production and its logs. The terminal opens in your browser: no SSH key, nothing to install.