lsof prints files that are currently open.

Documentation

man lsof https://manpages.debian.org/buster/lsof/lsof.8.en.html

wikipedia https://en.wikipedia.org/wiki/Lsof

Usage

lsof  # list files belonging to active processes

man lsof	https://manpages.debian.org/buster/lsof/lsof.8.en.html
wikipedia	https://en.wikipedia.org/wiki/Lsof