Which command shows which process is listening on TCP port 3000?

lsof -i :3000 lists the processes that have sockets on that port, with their PIDs. Use sudo to see processes owned by other users. ss -ltnp shows the same for listening sockets.

Why the others are wrong:
• ps aux | grep 3000 only matches the text "3000" in command lines.
• netstat -r prints the routing table.
• df -i shows inode usage on disks.