Most commands below need sudo.

Identify the process on a port

sudo fuser 80/tcp
# e.g. 80/tcp: 1234  → 1234 is the PID

Given a PID

Command line + user:

ps -p 1234 -o pid,user,cmd

Via /proc:

sudo cat /proc/<PID>/cmdline

Open files:

sudo lsof -p 1234

Environment variables:

sudo cat /proc/<PID>/environ | tr '\0' '\n'