Your Linux computer relies on a lot of background tasks called services or daemons. On systemd-based distributions you have built-in commands that let you see which services are running, disabled, or failed.

Services and daemons are background tasks that run without a user interface, don’t require human interaction, and are usually started as the computer boots up.

At one time, services were launched by init, which was the very first process to be launched. The details of the services were held in a collection of scripts located in the “/etc/init/d” directory. On non-systemd distributions that’s still the case.